Cdg final t_dversion2
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manual para el diagnostico de problemas y enfermedades en el maiz .Zea MAYS..http://www.lewishybrids.com/PDF/CDG_Final_TDversion2.pdf

manual para el diagnostico de problemas y enfermedades en el maiz .Zea MAYS..http://www.lewishybrids.com/PDF/CDG_Final_TDversion2.pdf

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Cdg final t_dversion2 Cdg final t_dversion2 Document Transcript

  • Table of ContentsIntroduction ....................................... . . . . . .............................................................1Examining a field .................................................................................................. 2Tips for shipping to diagnostic laboratories ................................................................ 2-3Stage I: Scouting from emergence to knee-high ............................................................. 4Stage II: Scouting from knee-high to tasseling .............................................................. 11Stage III: Scouting from tasseling to maturity ................................................................ 16Disease symptoms .............................................................................................. 24Leaf diseases ................................................................................................ 24-26Smutting diseases ...................................................... . . . . ..................................... 26Virus and virus-like diseases ...................................................... . . . . ......................... 27Fungal systemic diseases .......................................... . . . ..................................... 27-28Stalk and root rot diseases ................................................................................. 28-29Ear and kernel rots ...................................................... . . .................................. 29-30Insect injury symptoms and management recommendations ....................... . . . . . . . ......... 31-39Herbicide injury symptoms ................................................................................. 40-42Herbicides that may be used or trigger symptomology in corn ....................................... 43-47Herbicides listed by active ingredient and mode of action ............................................ 48-51Nutrient deficiency symptoms ............................................................................. 52-53Index ............................................................................................................... 54
  • IntroductionThis manual is prepared and distributed by Monsanto Company to help farmers, seed dealers, and companypersonnel determine the likely causes of abnormal corn plant appearance. While the primary target is the NorthAmerican Region, the principles and many of the situations described in this publication extend to the regions ofthe world where corn is grown.Symptoms may be due to a single cause or the result of two or more interacting factors. Also, because of theirdifferent genetic backgrounds, different hybrids may not have identical symptoms in response to the samecause. Routine field examinations are crucial in spotting problems or potential problems. Some growers em-ploy professional crop scouts rather than perform this function themselves. Weekly examinations are generallysufficient.Once a problem has been identified, its extent and severity must be determined to decide whether correctiveaction is necessary. Many pest management recommendations include threshold levels when control mea-sures will return a profit. Consult Cooperative Extension Service and chemical company recommendations forcontrol measures.1 Corn Diagnostic Guide
  • 1 Diagnosing Field Problems in CornEXAMINING A FIELDCarry the appropriate tools to help effectively scout or monitor fields. Some basic tools to have onhand include:• Tape measure • Small plastic bags• Knife • Water source• Trowel (6 or 8 inch) • Paper towels• Magnifying glass • Calculator• Clipboard and record keeping materials • Field marking flagsA spade and a set of nesting pails may be useful if considerable digging is expected. Digital camerascan be helpful in getting a record of insects or disease symptoms.Be very careful when making area-to-area or field-to-field comparisons. Many factors can influenceappearance, including: soil type, slope, and drainage; previous crops; fertility practices; seedbedpreparation; date, depth, and rate of planting; pest control; seed lot; and hybrid.Look for positives, not just problems. Observe and note hybrid differences, as well as the effects offertilizer and cultural practices.The following diagnostic key separates plant growth into three primary stages of crop development: Stage I Emergence to knee-high Stage II Knee-high to tasseling Stage III Tasseling to maturityIn the field, onset of symptoms might occur earlier or later than indicated, and may be observed duringmore than one growth stage.TIPS FOR SHIPPING TODIAGNOSTIC LABORATORIESTrained, experienced agronomists, crop protection, Some of these are more formally conducted thanresearch, and sales personnel stand ready to assist others, and cost of the service varies. Also, there areyou in diagnosing field problems. Local seed dealers a few private laboratories that are equipped to provideare your first contact when questions arise. Positive such services. Your local Cooperative Extensiondiagnosis often requires identification or confirmation Service office can suggest companies and provideof causes by a diagnostic laboratory. Most states have contact information.some arrangement, usually through their CooperativeExtension Service office, for accessing expert When preparing plant or soil samples for a diagnosis,diagnosis. follow these instructions offered by the laboratories. 2
  • 1. Provide representative samples of each problem observed. Visit a problem area twice, on observed, as well as a healthy sample from dates about a week apart, to determine unaffected plants or plant parts. whether the problem is intensifying, spreading, or disappearing.2. If sending leaf tissue, place sections of leaves showing disease symptoms between pieces of • Crop symptoms as observed in the field, dry paper toweling or notebook paper. such as “plants were wilted” or “leaves3. If sending the whole plant, remove excess soil appeared spotted.” Describe the size of from the roots and wrap the roots in moist paper area affected: spots, strips, or the entire toweling. Put roots and towel in a plastic bag. Do field. not place the entire plant in a plastic bag. Wrap • Percentage of plants affected. stem and leaves with paper, foil, or cardboard. • Soil type (clay, sand, muck, etc.).4. Do not add water or crush specimens unnecessarily. • Topography around affected plants, such as high ground, low ground, or gently5. Use a sturdy envelope or box for shipping. sloping.6. Avoid shipping at times that are likely to result in • Fertility level (include a soil test report, the parcel lying in a post office or freight depot if available) and the amount, kind, and over a weekend or holiday. Overnight delivery, timing of fertilizer application. early in the week, is strongly recommended. • Pesticides applied (fungicides, herbicides,7. Information will need to be provided with the insecticides, application rate, and date). plant specimen. Often, laboratories have specific forms that are required when submitting a • Soil moisture situation at and since sample. Information requested on such forms planting. If the field was irrigated, often includes the following: indicate the amount and dates of water application. • Variety (hybrid number) of crop. • Unusual recent air temperatures or • Location where sample was taken humidity conditions. (county, township, and town).. • Previous cropping and tillage history. • Date of planting, date problem was first observed, and date sample was • Types of weeds in the field. collected. Indicate whether the problem is better or worse than when first3 Corn Diagnostic Guide
  • 2 Stage I: Scouting from Emergence to Knee-HighDetermine the extent and severity of any problem identified. Is the problem throughout the field orspotty and localized? Has emergence been completed or are there seeds sprouted, ready to emerge?Take accurate stand counts and determine percent of stand achieved.If replanting is necessary, take steps to prevent recurrence of the cause for poor emergence. Verify thatthe planter is operating properly and that fertilizer or pesticide issues have been corrected. number of plants established % stand achieved = X 100 number of seeds planted If the stand is uneven or if there are skips down the row, dig to find the planted seed and its distribution.GENERAL SYMPTOM POSSIBLE CAUSE REMARKS1. No seed • Planter Improper adjustment; row unit drive not engaged; worn parts; clogged spout; empty box or tank; wrong plates, disks, or drum; excess or wrong seed treatment. • Rodents or birds Digging and partly-eaten kernels.2. Normal seed • Unfavorable soil conditions Cold, dry soil. appearance; not • Poor seed-soil contact Inadequate press wheel pressure; improper swelled closing wheel adjustments; inadequate residue management; dry or cloddy soil.3. Normal seed • Unfavorable soil conditions Cold, wet soil. appearance; • Fertilizer or pesticide injury Phytotoxic pesticides or too much fertilizer swelled but not too close to the seed. sprouted4. Seed dead, rotted • Seed rots or seedling blights These are accentuated when soil conditions are unfavorable for germination and seedling growth. Many species of fungi and/or bacteria may be involved. Fungicide seed treatment protects the seed, not the seedling. 4
  • GENERAL SYMPTOM POSSIBLE CAUSE REMARKS4. Seed dead, rotted • Fertilizer injury Fertilizer salts, nitrogen, and potassium draw (cont.) moisture and may leave seed in soil too dry to support growth. In-furrow applications are more likely to cause fertilizer injury than starter fertilizers placed at least 2 inches from the seed. Ammonia toxicity is caused when planting follows anhydrous or aqua ammonia application too closely or where application was too shallow. This can kill or stunt seedlings. Roots appear sheared off. Boron and some other micronutrients impair germination if they are too close to the seed. • Insecticide injury Some soil-applied organophosphate insecticides can impair germination if placed in furrow with the seed. Check the label and apply only as directed. • Dead seed planted • Unfavorable soil conditions Cold, dry, wet, or crusted soil.5. Seed hollowed out • Insects Seed corn beetle, seed corn maggot, or wireworm (see pp. 36-38).6. Sprout twisted or • Unfavorable soil conditions Crusted, cold, or cloddy soil. A cloddy leaves expanded surface can allow light to reach the sprout below ground and trigger leafing too soon. In the case of crusting, rotary hoeing may be beneficial. • Seed planted too deep • Mechanical injury to seed in handling or planting • Chemical injury Fertilizer (see p. 5); insecticides (see p. 5); or some herbicides such as acetanilides and dinitroanilines (see pp. 41-42).7. Slow, uneven • Planter Seed injury due to improper operation or emergence adjustment, including planting depth. • Unfavorable soil conditions Cold, dry, wet, or crusted soil. In the case of crusting, rotary hoeing may be beneficial. Properly banded fertilizer at planting may help seedlings overcome unfavorable soil conditions. • Seed planted too deep5 Corn Diagnostic Guide
  • If plants are abnormal in appearance, try to identify one of the following specific symptoms.GENERAL SYMPTOM POSSIBLE CAUSE REMARKS1. Seedlings pulled • Bird or rodent damage Chemical repellents may help. or dug up, seed eaten2. Slow, uneven plant • Unfavorable growing Cold, dry, wet, or compacted soil. Properly growth conditions banded fertilizer at planting may help minimize the effects of some unfavorable growing conditions. • Low fertility If a nutrient deficiency due to inadequate amounts in the soil, is confirmed, consider sidedressing or foliar application, depending on the nutrients involved (see pp. 52-53). • Insects attacking roots Corn root aphid, corn rootworm, grape colaspis, webworm, white grub, or wireworm (see pp. 31-38). • Nematodes attacking roots Requires microscopic analysis. • Chemical injury Fertilizer (see p. 5); insecticides (see p. 5); herbicides such as Balance®; Command® or Scepter® carryover (see pp. 41-42); or liquid manure. • Non-uniform planting depth • Failure of secondary roots Dry, loose soil is not conducive to normal to develop (rootless corn root development. This condition is syndrome) accentuated by shallow planting and whipping by wind. Cultivation may help by throwing soil around the base of plants.3. Discolored leaves • Nutrient deficiency Magnesium, nitrogen, phosphorus, or sulfur (see pp. 52-53). Nitrogen deficiency results in a yellow discoloration of leaves. Phosphorus deficiency results in a purpling of leaves due to the accumulation of anthocyanins. If nutrient deficiency is confirmed, consider sidedressing or foliar application, depending on the nutrients involved. • Unfavorable soil conditions Waterlogged, cold, or compacted soil. These conditions can also affect nutrient uptake and translocation. 6
  • GENERAL SYMPTOM POSSIBLE CAUSE REMARKS3. Discolored leaves • Insects attacking roots Most observed leaf discoloration is due to (cont.) nutrient deficiency induced by damaged or inadequate roots (see nutrient deficiency, above). • Nematodes attacking roots Requires microscopic analysis. • Chemical injury Fertilizer (see p. 5); insecticides (see p. 5); herbicides such as Balance®; Command® or Scepter® carryover (see pp. 41-42); liquid manure. • Wind damage Abrasion by sand or soil particles. Difficulty establishing secondary roots. • Frost or freeze Check growing point for damage. Seedlings often recover. Most pronounced in low-lying areas. • Cold (not freezing) Cool nights and warm days promote above- temperature stress ground plant growth at the expense of root development. This leads to increased demand by the above ground tissues for more nutrients than the roots can deliver. The result can be short-term deficiency symptoms until the root system becomes more developed. • Anhydrous burn • Mechanical injury • Hybrid differences Uneven Corn Plant Growth7 Corn Diagnostic Guide
  • GENERAL SYMPTOM POSSIBLE CAUSE REMARKS4. Leaves rolled or • Drought puckered, may be • Insects attacking roots or See Section 6, Insect Injury Symptoms wilted stalks (p. 31-38), plus chinch bug, cutworm, Japanese beetle, stink bug, or webworm. • Nematodes attacking roots Requires microscopic analysis. • Mechanical root pruning5. Leaves rolled or • Herbicide injury Acetanilides, dinitroanilines, or phenoxys twisted together (see pp. 41-42). (“onion leaf” or • Temperature variation Alternating hot and cold weather, inducing “buggy whip”) very rapid growth spurts followed by little or no growth. • Nutrient imbalance Boron toxicity or calcium deficiency (see p. 52). • Hail damage Injury to the growing point at this growth stage can result in short-term wrapping of leaves.6. Shredded leaves • Wind damage or eaten plants • Hail damage • Insects Armyworm, common stalk borer, corn earworm, cutworm, European corn borer, grasshopper, slug, or webworm (see pp. 32-37). • Livestock or wild animal Look for tracks. grazing7. Leaves spotted, • Wind damage Abrasion by sand or soil particles. striped or dead • Low soil pH Beaded streaking of leaves, which turn reddish-purple and may die. • Nutrient deficiency Boron, copper, magnesium, potassium, sulfur, or zinc (see pp. 52-53). • Insects Flea beetle, leaf miner, or thrips (see pp. 35-37). • Disease Anthracnose, bacterial wilt, eyespot, Goss’s wilt, holcus spot, seedling blights (favored by cool, wet soil), virus or virus-like diseases (see pp. 24-27). • Fertilizer or herbicide injury Anhydrous burn; spray drift; foliar-applied herbicides such as Buctril®, Basagran®, Gramoxone®, or Blazer®; Classic®, Scepter®, or Reflex® carryover; premix acentanilides post-applied (see pp. 40-42). 8
  • GENERAL SYMPTOM POSSIBLE CAUSE REMARKS7. Leaves spotted, • Sunscald or cold Cold nights followed by clear, bright, fast- striped or dead warming days. (cont.) • Hybrid differences8. Rows of holes • Insects Billbug, common stalk borer, corn borer, across leaves cutworm, or stink bug (see pp. 32-37).9. Plants wilt and • Insects Billbug, chinch bug, cutworm, stink bug, die suddenly white grub, or wireworm (see pp. 32-38). • Wind damage • Disease Seedling blights, bacterial wilt, or Goss’s wilt (see p. 26). • Herbicide injury Triazines or misapplications of glyphosate herbicides (see pp. 41-42). • Frost or freeze Check growing point for damage. Seedlings often recover. • Lightning Kills everything, usually in circular area. • Anhydrous burn • Flooded, water-logged soil “Buggywhip” Corn plant two days after frost9 Corn Diagnostic Guide
  • GENERAL SYMPTOM POSSIBLE CAUSE REMARKS10. Plants twisted or • Herbicide injury Especially 2,4-D followed by wind (see pp. broken off 41-42). • Insects Billbug, cutworm, lesser cornstalk borer, or stinkbug (see pp. 32, 36-37).11. Inhibited root • Nematode injury Requires microscopic analysis. development or • Insects Corn rootworm, grape colaspis, white grub, malformed roots or wireworm (see pp. 34-38). • Fertilizer injury • Herbicide injury Phenoxys, Banvel®, carryover dinitroanilines, and Scepter® or Classic® carryover (see pp. 41-42). • Soil conditions Planting when soils are too wet can cause sidewall compaction that can arrest or severely restrict corn root development. Look for flat-sided or abruptly arrested root systems. Wind Damage in Corn Field Hail Damage in Corn Field 10
  • 3 Stage II: Scouting from Knee-High to TasselingThis is the period of most rapid plant growth. Nutrient and moisture demands are high; deficiencies willlikely reduce crop yield potential. Problems must be evaluated for economic damage potential beforecontrol decisions can be made. Observe differences due to hybrids and management practices. If plants are abnormal in appearance, try to identify one of the following specific symptoms.GENERAL SYMPTOM POSSIBLE CAUSE REMARKS1. Uneven height • Emerged at different times Uneven planting depth; uneven soil (tall plants, short moisture. plants) • Varied nutrient or moisture availability under drought conditions • Low soil pH • Herbicide drift Use of burndown products adjacent to cropped area. • Nutrients concentrated at dry Nutrients are unavailable to the plant. soil surface • Fallow (idle land) syndrome Phosphorus is unavailable to the plant (see p. 53).2. Numerous tillers • Growing point injury Mechanical or insect damage. • Favorable early-season Optimum moisture, high soil fertility, or both. growing conditions • Low plant population • Adjacent to open spaces (population gaps) in the row • Hybrid differences • Disease Crazy top (see p. 27)3. Discolored or • Nutrient deficiency Nitrogen, phosphorus, or potassium (see dead leaves p. 53).11 Corn Diagnostic Guide
  • GENERAL SYMPTOM POSSIBLE CAUSE REMARKS3. Discolored or dead • Fertilizer or herbicide injury Fertilizer or herbicide on foliage. This tends leaves (cont.) to be more pronounced at row ends or where overlap application was made. • High temperatures Noted as scalding or bleaching of top leaves first. • Sunscald or cold banding Cold nights followed by clear, bright, fast- warming days. • Insects Chinch bug, spider mite, or root-attacking insects, which can reduce nutrient uptake (see pp. 32-37). • Mechanical injury • Frost or freeze • Hybrid differences • Barren stalk Purpling or reddening due to anthocyanin expression in response to accumulation of sugars that cannot translocate to the initiating ear.4. Whorl leaves dead • Disease Bacterial stalk rot (see p. 28). (“deadheart”) • Insects Billbug, corn borer, or fall armyworm (see pp. 32-33). • Chemical injury More common following a late over-the-top application of certain herbicides. • Excessive heat Temperature exceeding 100°F, depending on moisture availability and genetics of the hybrid.5. Leaves spotted • Low soil pH Beaded streaking of leaves, which turn or striped reddish-purple and may die. • Nutrient deficiency Boron, iron, magnesium, manganese, nitrogen, or potassium (see p. 52-53). • Chemical injury Herbicides, additives’ reactions, or fertilizers; symptoms may be due to spray drift on foliage. • Disease Bacterial leaf blight, eyespot, Goss’s wilt, holcus spot, leaf blights, Physoderma brown spot, rust, sorghum downy mildew, virus or virus-like diseases (see pp. 24-28). 12
  • GENERAL SYMPTOM POSSIBLE CAUSE REMARKS5. Leaves spotted or • Insects Cereal leaf beetle, corn rootworm beetle, striped (cont.) corn blotch leaf miner, flea beetle, spider mite, or thrips; root-damaging insects induce nutrient deficiency or drought symptoms (see pp. 32-37). • Wind damage Abrasion by sand or soil particles. • Hail damage • Genetic stripe Observed only on occasional plants. • Sunscald or cold banding Cold nights followed by clear, bright, fast- warming days.6. Leaves eaten or • Livestock or wild animals Look for tracks. shredded • Insects Armyworm, billbug, common stalk borer, corn borer, corn earworm, cutworm, grasshopper, Japanese beetle, leaf miner, slug, or wireworm (see pp. 32-38). • Hail damage Determine if the growing point survived. If it did not, plant will not produce a tassel. Despite this, ear fertilization may still occur. • Wind damage • Disease Sorghum downy mildew (see p. 28).7. Plants stunted, • Virus or virus-like diseases Corn lethal necrosis, corn stunt leaves close spiroplasma, maize chlorotic dwarf, or together with maize dwarf mosaic (see p. 27). mosaic mottle or streaks; leaves yellow or red8. Gray or black galls • Disease Common corn smut (see p. 26). growing on plants9. Stalks spindly, • Nutrient deficiency See pp. 52-53. unthrifty, yellow • Excess soil moisture • Excessive plant population • Root damage Insects, nematodes, chemical, or mechanical. • Stalk damage Insects, disease, or mechanical.10. Plants wilted or • Drought rolled • Root damage Insects, nematodes, chemical, or mechanical. • Stalk damage Mechanical or insects; chinch bug, common stalk borer, or corn borer (see pp. 32-33).13 Corn Diagnostic Guide
  • GENERAL SYMPTOM POSSIBLE CAUSE REMARKS11. Top leaves tightly • Chemical injury 2,4-D and other phenoxy herbicides; Banvel® rolled (“buggy (see p. 41). whip” or “onion • Cold soil during seedling leafing”) stage • Temperature response or Alternating hot and cold periods, speeding rapid growth syndrome and slowing plant growth. • Nutrition Boron toxicity or calcium deficiency (see p. 52). • Mechanical injury • Hybrid differences12. Plants growing • Recovery after root damage Insects (usually, but not limited to corn up in a curved rootworm larvae), nematodes, herbicides “gooseneck” (especially phenoxys), soil compaction, mechanical injury, or wind. • Recovery after early season environmental conditions13. Curled or stubby • Wind and wet soils brace roots • Dry, hot soil surface • Wind action14. Plants twisted or • Mechanical injury growing off at 90˚ angle15. Plants leaning or • Wind damage Especially if soil is wet. Wind can cause broken off greensnap at lower nodes of rapidly growing stalk. • Livestock or wild animals Look for tracks. • Root damage Insects, nematodes, chemical, or mechanical. • Insects attacking stalk Common stalk borer or corn borer (see p. 32-33). • Chemical injury, especially if Especially Banvel® or phenoxy herbicides followed by wind (see pp. 39-41). • Soil compaction Inadequate root development. • Poor secondary root Rootless corn syndrome due to weather development in dry soil and aggravated by shallow planting. • Disease Bacterial or Pythium stalk rots (see pp. 28-29). • Hail damage 14
  • GENERAL SYMPTOM POSSIBLE CAUSE REMARKS16. Plants wilt and • Lightning Kills everything, usually in a circular area. die suddenly • Drought Field areas with low water-holding capacity are first to show stress. • Disease Bacterial or Pythium stalk rots (see pp. 28-29). • Frost or freeze • Herbicide injury Misapplication of glyphosate, glufosinate, paraquat, or other non-selective herbicides (see pp. 41).17. Tassel feeding • Insects Armyworm, corn leaf aphid, or western (while in whorl) bean cutworm (see pp. 32-35).18. Tassels proliferated • Disease Crazy top (see p. 27). into green cluster of fingerlike branches, excessive tillering, leaves often thick and straplike19. Tassel proliferated, • Disease Head smut (see p. 26). with stringy black vascular bundles present “Greensnap” at lower nodes of rapidly growing corn stalk15 Corn Diagnostic Guide
  • 4 Stage III: Scouting from Tasseling to MaturityThis period, which commences with the critical pollination stage, includes grain fill, plant maturation,and death. It also includes the critical stage before harvest when standability and ear retention becomeconcerns. Field observations are essential to detect yield-depressing factors during this period. If LEAVES are affected, try to identify one of the following specific symptomsGENERAL SYMPTOM POSSIBLE CAUSE REMARKS1. Eaten • Livestock or wild animals Look for tracks. • Insects Armyworm, corn borer, corn rootworm beetles, grasshopper, or Japanese beetle (see pp. 32-36).2. Shredded • Hail damage • Wind damage • Disease Sorghum downy mildew (see p. 28).3. Dead “frosted” • Frost or freeze appearance • Drought • Disease Anthracnose, leaf blights, or stalk and root rots (see pp. 24-26; 28-29). • Insects Corn borer, corn leaf aphid, or spider mite (see pp. 31-33; 37).4. Spotted or dead • Disease Numerous leaf blights such as anthracnose, eyespot, Goss’s wilt, gray leaf spot, Helminthosporium leaf spot, northern corn leaf blight, Phaeosphaeria leaf spot, Physoderma brown spot, rust, or southern leaf blight (see p. 26). • Chemical injury Especially spray drift.5. Discolored • Insects Corn leaf aphid (see p. 31). sheath • Disease Purple sheath spot caused by saprophytic organisms existing on pollen trapped between the leaf sheath and stalk. 16
  • GENERAL SYMPTOM POSSIBLE CAUSE REMARKS6. Red or purple • Mechanical injury color • Barren plant Anthocyanins develop in response to accumulation of sugars that cannot be translocated to filling grain. • Disease Corn rust, corn stunt spiroplasma, high plains virus, or maize chlorotic dwarf (see pp. 24-27). • Insects Corn borer (see p. 33). • Hybrid differences7. White striping • Disease Sorghum downy mildew (see p. 28). with white, downy growth on upper and lower leaf surfaces If SILKS are affected, try to identify one of the following specific symptomsGENERAL SYMPTOM POSSIBLE CAUSE REMARKS1. Eaten off • Insects Armyworm, corn earworm, corn rootworm beetle, grasshopper, Japanese beetle, or western bean cutworm (see pp. 32-35).2. None visible, or • Heat delayed several • Drought days after • Nutrient deficiency or Especially nitrogen or phosphorus. tasseling imbalance • Temperature variation Cold nights occurring just prior to silking. • Insects Corn leaf aphid, fall armyworm, or spider mite (see pp. 31-32; 37). • Excessive population for conditions3. Trapped, balled • Drought within the husk • Nutrient deficiency or See pp. 52-53. imbalance • Temperature variation Cold nights during early silking. • Hybrid differences17 Corn Diagnostic Guide
  • GENERAL SYMPTOM POSSIBLE CAUSE REMARKS4. Red or green color • Hybrid differences Fresh silk color is genetically controlled. If TASSELS are affected, try to identify one of the following specific symptomsGENERAL SYMPTOM POSSIBLE CAUSE REMARKS1. Failed to emerge • Drought or heat stress • Nutrient deficiency Especially boron (see p. 52-53). • Insects Aphid stress, corn earworm, or fall armyworm (see pp. 31-32).2. A mass of leaves • Disease Crazy top, head smut, or sorghum downy mildew (see pp. 27-28).3. One or more small • Genotype by environment Most common on tillers. ears formed interaction4. Kernels develop in • Genotype by environment Most common on tillers. tassel interaction5. Broken off, stalk • Insects Corn borer (see p. 33). tunneled If STALKS are affected, try to identify one of the following specific symptomsGENERAL SYMPTOM POSSIBLE CAUSE REMARKS1. Red or purple • Mechanical injury to plant color • Barren stalk Anthocyanins develop in response to accumulation of sugars that cannot be translocated to filling grain. • Hybrid differences • Insects When corn borers tunnels into a stalk, the area above the point of entry may turn red or purple. 18
  • GENERAL SYMPTOM POSSIBLE CAUSE REMARKS2. Barren (no ear • Drought enlargement) • Heat • Nutrient deficiency or See pp. 52-53. imbalance • Insects Corn leaf aphid or spider mite (see pp. 31, 37). • Silks eaten off prior to Corn rootworm beetle and Japanese pollination beetle (see pp. 34-36). • Disease Head smut, mildews, virus or virus-like disease (see pp. 26-27). • Excess population for conditions • Tillers Seldom produce a fully-developed ear. • Timing of silk or pollen shed Environmental stress. disrupted • Mechanical injury3. Broken below ear • Wind Plants just prior to tasseling are especially vulnerable to greensnap by wind. • Disease Stalk and root rots (see pp. 28-29). • Nutrient imbalance Excess nitrogen, insufficient potassium (see p. 53). • Insects Southwestern corn borer (see p. 33). • Weather stress Drought, heat, or other conditions limiting photosynthesis. • Mechanical injury Machinery; livestock or wild animals. • Excessive population for conditions • Delayed harvest4. Broken above ear • Wind • Insects European corn borer or fall armyworm (see pp. 32-33). • Mechanical injury Machinery; livestock or wild animals. • Delayed harvest5. Multiple ears at • Hybrid differences one node • Mechanical injury19 Corn Diagnostic Guide
  • GENERAL SYMPTOM POSSIBLE CAUSE REMARKS5. Multiple ears at • Cold temperature when ears one node (cont.) formed • Disease Mildews, virus or virus-like disease (see pp. 27-28). • Insects Results from severe silk clipping by insects such as corn rootworm beetle and Japanese beetle (see pp. 34, 36).6. Leaning, but • Wind and wet soil not broken (root • Poor root development Drought, fertilizer placement, soil lodged) compaction, low soil pH, or poorly drained soil. • Insects Corn rootworm and other root feeders (see pp. 34-35). • Nematode activity • Disease Stalk and root rots (see pp. 28-29). • Nutrient deficiency Especially potassium (see p. 53). • Herbicide injury Especially 2,4-D and other phenoxys (see p. 41). • Mechanical injury Machinery, livestock or wild animals • Delayed harvest • Hybrid differences7. Premature death • Disease Leaf blights or stalk and root rots (see pp. 24-26, 28-29). • Insects Corn borer (see p. 34). • Frost or freeze • Severe drought • Lightning Kills everything, usually in a circular area.8. Black mold • Saprophytic Buildup on dead stalk tissue under warm, humid weather conditions. Timely harvest will deter. If EARS are affected, try to identify one of the following specific symptomsGENERAL SYMPTOM POSSIBLE CAUSE REMARKS1. Numerous ear • Disease Crazy top, sorghum downy mildew, virus or shoots, leafy and virus-like diseases (see pp. 27-28). barren 20
  • GENERAL SYMPTOM POSSIBLE CAUSE REMARKS2. Soft, glistening • Disease Common corn smut (see p. 26). smut galls, black and powdery when mature3. Poorly filled tips • Hybrid differences • Nutrient deficiency Especially nitrogen or potassium (see p. 53). • Interaction between population, hybrid, and environment • Insects Silks clipped before pollination. Corn borer, corn earworm, corn rootworm beetle, fall armyworm, or Japanese beetle (see pp. 33- 36). • Disease Foliar disease that reduce photosynthesizing area (see pp. 24-26). • Drought Silks at ear tips were not present when pollen was available • Unusually favorable growing Cob elongates, but rarely fills up tip kernel. conditions after pollination • Suboptimum light, carbon Reduced photosynthesis; tip kernels abort. dioxide, or temperature during kernel fill4. Small malformed, • Nutrient deficiency Especially nitrogen and phosphorus (see p. 48). light weight • Drought or heat stress • Plant damage Mechanical or disease. • Excessive population for conditions • Second or third ear on stalk, or on a tiller • Insect-caused plant stress Numerous ear-feeding insects (see pp. 32-38). • Disease Leaf blights, stalk and ear rots, virus or virus- like diseases (see pp. 24-30). • Soil compaction5. Very short husk, • Weather Usually observed after drought or heat has remains tight at stopped husk growth, but later favorable maturity; ear tip conditions permit more normal ear size to exposed develop. • Hybrid differences21 Corn Diagnostic Guide
  • GENERAL SYMPTOM POSSIBLE CAUSE REMARKS6. Barren (little to no • Disease Head smut, virus or virus-like diseases (see grain) pp. 26-27). • Pollination failure Drought, heat, or other stress interfered with silk/pollen shed timing; insect (clipped silks or caused tassel to abort); chemical injury (especially by growth regulators like 2,4-D and Banvel®). • Pesticide injury Following drift or misapplications.7. Pinched ear • Chilling injury during early ear Also called beer can ear. Ear is reduced syndrome development to 3-4 inches. Well filled kernels are on bottom third of ear, cob tissue on middle third, and undeveloped tissue on top third.8. Dropped • Drought Weakened shank. • Nutrient deficiency Weakened shank. • Hybrid differences Ears usually drop free of husk. • Insect damage to shank Husk usually remains on the dropped ear; European corn borer (see p. 33).9. Scattered kernel • Lack of adequate viable pollen set when silks are receptive • Silks eaten off before Insect or animals. pollination • Heat or drought at pollination • Nutrient deficiency • Herbicide injury Phenoxy herbicides or too-late applications of glyphosate (see p. 41).10. Kernel feeding • Insects Corn borer, corn earworm, fall armyworm, picnic beetle, or western bean cutworm (see pp. 33-35). • Birds, animals11. Rotten (spots or • Disease Ear and kernel rots or Helminthosporium entire ear) leaf spot (see pp. 29-30; 25). • Insects Corn borer, corn earworm, fall armyworm, picnic beetle, or western bean cutworm (see pp. 33-35). Followed by weathering or disease. • Birds Followed by weathering or disease. • Hail or other mechanical injury Followed by weathering or disease. 22
  • GENERAL SYMPTOM POSSIBLE CAUSE REMARKS12. Kernels eaten • Birds from ear tips • Wild animals or rodents • Insects Corn earworm, fall armyworm, picnic beetle, or western bean cutworm (see pp. 33-35).13. Tunnels in ear, • Insects Corn borer, corn earworm, or fall armyworm cob, shank, or (see pp. 32-33). stalk If KERNELS are affected, try to identify one of the following specific symptomsGENERAL SYMPTOM POSSIBLE CAUSE REMARKS1. Broken seedcoat, • Genetic and environment Popped kernels usually occur under high “popped” interaction temperatures. appearance2. Horizontally cut or • Silk-cut A genetic and environment interaction. Not split seedcoat visible until kernels are shelled from the cob.3. Pink or red • Kernel red streak Caused by toxin secreted during feeding of streaking or wheat curl mite. More pronounced toward lengthwise stripes, ear tip. No detrimental effects are known. especially running over crown4. Sprouted • High rainfall and warm Usually accompanied by mold. especially at base temperature while ear of ear remained erect on stalk5. White streaking, • Disease Associated with Fusarium ear rot. also known as “starburst” Barren corn Pinched ear syndrome23 Corn Diagnostic Guide
  • 5 Disease SymptomsThis section will help you identify the common corn diseases based on plant symptoms and conditions. Itis not uncommon to have symptoms of several different diseases present at the same time. Symptoms ofdifferent diseases may appear similar, particularly during early stages of disease development. Laboratoryculturing and microscopic examination may be required to make a positive identification.Growth stages during which symptoms generally appear are listed following the disease name and aredescribed as follows: Stage I Emergence to knee-high Stage II Knee-high to tasseling Stage III Tasseling to maturityLEAF DISEASES The more common leaf blight phase appears after tasseling. Leaves are streaked with gray-green toAnthracnose (Stage I, III) yellow-green lesions, each distinguished by the Oval to spindle-shaped presence of a flea beetle feeding scar toward the water-soaked lesions on base of the streak. Streaks are long and irregular, youngest leaves turn tan turning tan as the tissue dies. to brown with yellow to reddish brown borders. Flea beetles (small, oval, black insects) are the Heavily infected leaves primary carrier. Incidence of the disease is relative wither and die. Top-leaf to beetle population. Sweet corn tends to be more die-back may occur 4 sensitive than field corn to this disease. weeks to 6 weeks after Common Corn Rust (Stage II, III) pollination, leaving the Cinnamon-brown,lower stalk green. The organism thrives in warm, powdery, circular-to-humid weather. The stalk-rot phase of the organism elongated pustules (blister-is of greater concern than the leaf blight phase. like growths) can occurBacterial Wilt and Bacterial Leaf Blight on any aboveground plant(Stewart’s Wilt, Stewart’s Disease) (Stage I, III) tissue, but especially on both surfaces of the Young plants exhibit long, leaves. In contrast, green-gray, water-soaked pustules of southern corn lesions with wavy margins, rust occur primarily on accompanied by stunting the upper leaf surface. Pustules rupture leaf surface and wilting which lead to and rusty “powder” can be rubbed off with fingers. plant death. Cavities may Pustules become dark brown to black late in the form in stalk near the soil growing season. The organism thrives in moderate line. Bacterial masses ooze from cut end of infected to cool temperatures and high humidity. stalks or leaves. 24
  • Eyespot (Stage II, III) Helminthosporium Leaf Spot Small (less than ¼ inch), (Northern Leaf Spot) (Stage III) circular, translucent lesions Numerous races of the surrounded by a yellow to organism have been purple margin, give a halo identified. Symptoms vary effect. Lesions occur on by race. Lesions tend to leaves (most commonly as be oblong to blocky, and plants approach maturity), tan to brown in color. This sheath and husk. The leaf spot may also cause a disease is favored by cool, black, charred-appearing moist weather. ear rot. It prefers moderate temperaturesGoss’s Wilt and high humidity.(Leaf Freckles and Wilt, Nebraska BacterialWilt and Leaf Freckles) (Stage I, III) Holcus Spot (Stage I) Young plants wilt and This organism causes die. Vascular bundles are small, circular to oblong, discolored. More common water-soaked lesions later-season infections toward tips of lower produce dull gray-green leaves. Later, lesions to orange lesions forming become creamy white to water-soaked streaks tan, then light brown with with irregular margins on reddish margins. Holcus leaves. Within developing spot is very similar in lesions, small, irregular appearance to paraquatshaped water-soaked “freckles” appear. Bacterial damage. Rainstorms accompanied by wind splashdroplets may ooze from the leaf surface early in overwintering bacteria from the residue onto youngthe morning. Plant injury, such as from hail or wind plant leaves. This organism does not cause seriousdamage, enhances infection. loss.Gray Leaf Spot (Stage III) Northern Corn Leaf Blight (Stage II, III) Gray to tan, rectangular Long (up to 6 inches), lesions on leaf, sheath or elliptical, gray-green husk tissue. Spots are lesions that become tan- opaque and long (up to brown identify infections 2 inches). Lower leaves caused by this organism. are affected first, usually Infection spreads up the not until after silking. plant starting on lower The organism thrives leaves. It is favored by high in extended periods of humidity and moderate warm, overcast days and temperatures. Numeroushigh humidity. It has become more prevalent with physiologic races have been described. Host specificincreased use of reduced tillage and continuous races of the organism may also attack sorghum.corn.25 Corn Diagnostic Guide
  • Phaeosphaeria Leaf Spot (Stage III) rust pustules attack upper and lower leaf surfaces Lesions are initially small, and readily break through the epidermis.) This round to oval, pale green organism is favored by warm, humid weather. or yellow, and scattered on leaves of mature plants. SMUTTING DISEASES Spots become light Common Corn Smut tan with reddish-brown (Boil Smut, Blister Smut) (Stage I, II, III) margins and may coalesce Local infection of any into irregularly shaped plant part, even below lesions. This disease is the soil surface, occurs most prevalent in areas of through plant wounds orhigh rainfall and moderate temperatures. thin-walled cells of activelyPhysoderma Brown Spot (Stage I, III) growing tissue. Resulting Small yellow spots appear first at the base of the leaf. These spots become brown and combine to form chocolate-brown to galls are first silver-white, reddish irregular blotches, then become gray to sometimes as bands black powdery masses of infection across leaf of smut spores that are blades. Sheath, husk, released when the galls tassel, stalk, and leaves break open. Galls onmay exhibit symptoms late in the season. Infected leaves seldom develop beyond pea-size and tend tostalks may break at a node. This organism is favored harden and dry without rupturing. High fertility andby warm, wet weather. plant injury favor the disease. Common smut is notSouthern Corn Leaf Blight (Stage II, III) toxic to animals. The most common race, Head Smut (Stage III) named “O,” produces small, Seedling infection results elongated (up to 1 inch in systemic development long), parallel-sided lesions of the disease as the plant that are tan with brownish grows and develops. borders. This blight primarily Tassels of affected plants attacks leaves. It is favored may multiply as a mass of by high humidity and warm leaves or be replaced by a temperatures. black, smutty mass which ruptures to release spores,Southern Corn Rust (Stage II, III) leaving black, thread-like Small, circular, orange- vascular strands. Ears may be completely replaced to-light-red pustules by similar, often triangular-shaped, smut masses. (blister-like swelling) occur Occasionally, part of an ear escapes and produces on leaves, especially a few kernels. Hot, dry soil at seedling stage favors the upper surface, and infection. One type of head smut also attacks sheaths. Pustules rarely sorghum. break the leaf surface. (In contrast, common corn 26
  • VIRUS AND VIRUS-LIKE DISEASES Maize Chlorotic Dwarf VirusCorn Lethal Necrosis (CLN) (Stage II, III) (MCDV) (Stage II, III) Younger leaves are yellow Mosaic patterns appear on and finely striped. There leaves and husk. Leaves is a general yellowing die from the margins or reddening of leaves inward and plants may and plants are stunted. die prematurely. The Most affected plants are organism generally starts barren. MCDV is spread by at the tassel and works leafhoppers from infected downward. Barrenness Johnsongrass and other or sharply reduced grain host species. MCDV is production is common. detected more frequently and is more damaging thanCLN is caused by synergistic interaction whenplants become infected by maize chlorotic mottle maize dwarf mosaic.virus and either maize dwarf mosaic virus or wheat Maize Dwarf Mosaic Virusstreak mosaic virus. Presently, the disease has been (MDMV) (Stage II, III)identified only in parts of Kansas and Nebraska. Mottling of younger leaves progresses into narrow,Corn Stunt Spiroplasma (CSS) (Stage II, III) light-green to yellowish Corn stunt is caused streaks along leaf veins. by a spiroplasma, not a Leaves, sheaths and husks virus. Margins of whorl may show symptoms. leaf turn yellow followed Plants are stunted and by reddening of older ear size and seed set are leaves and yellow striping reduced. Sometimes, which runs the length of multiple tillers or ear shoots leaves. Plants are stunted, develop. MDMV is most prevalent in areas where UGA1235014 have multiple tillers and Johnsongrass grows and serves as a winter host for produce numerous small the virus. It is spread by aphids.ear shoots. Root systems are reduced. Corn stuntsymptom development and epidemiological patterns FUNGAL SYSTEMIC DISEASESare similar to those of virus diseases. Crazy Top (Stage II, III)High Plains Virus (HPV) (Stage I, II, III) Plants have excessive Symptoms begin as small tillering with rolling or yellowish flecks which twisting of newer leaves. often appear as lines The tassel becomes a running parallel to leaf mass of leaves; ears, if veins. Infected seedlings present, often do likewise. turn bright yellow and Leaves are usually narrow, quickly die. Plants may thick and appear strap- be stunted, older leaves like. Occasionally over- 536657 may become red and sized plants will develop. then necrotic, and ear and Infection occurs when young plants are underkernel size may be reduced. Considerable symptom flooded soil conditions; therefore, it is more frequentvariation exists among cultivars. It is spread by the in low-lying areas. This is one of numerous downywheat curl mite. mildews that attack corn.27 Corn Diagnostic Guide
  • Sorghum Downy Mildew (Stage II, III) stalk than with other stalk rots. The same organism Leaves are yellow with causes leaf blighting earlier in the season. white stripes; plants are stunted and ears and Bacterial Stalk Rots (Stage II, III) tassels multiply into leafy At least two organisms masses. Often the base have been identified as of leaves are chlorotic causing bacterial stalk rot. and sharply contrast with With either, there is rapid healthy green leaf tips. development of a soft rot White, downy growth of stalks, accompanied appears on either or both by wilting and plantleaf surfaces. Leaves often split or shred. This is death. Stalks twist andprimarily a disease of sorghum. 5361254 collapse while still green, disintegrating into a softSTALK AND ROOT ROT DISEASES mass often accompanied by a foul odor.Stalk rots are diseases that are most commonlyexpressed as plants reach maturity. Stalk rot of Charcoal Rot (Stage III)corn tends to be a complex of several disease- Charcoal rot can becausing fungi and sometimes bacteria; seldom will expected when the croponly one causal organism be isolated and identified. has grown under hot, dryPlants with rotted stalks almost always have rotted conditions; it also attacksroots, too. Usually, but not always, the same causal sorghum and soybeans.organisms are involved. Visual identification is very Lower internodes are affected, causingdifficult. premature ripening,Typically, wilting is the first sign of stalk rot in a field. shredding, and crownIn a few days, leaves turn a “frosted” gray, ears disintegration. Vasculardroop and the outer rind of the lower stalk turns strands remain intact but are black or “charred” inbrown. Fields where stalk rot is developing should be appearance. Stalks become gray-black or charcoalharvested early to reduce grain losses. color.Anthracnose Stalk Rot (Stage II, III) Diplodia (Stenocarpella) Stalk Rot (Stage III) Early infection may kill Lower internodes are plants before pollination, straw-brown, spongy, and but onset usually occurs dry. Pith disintegrates, just before plants mature. leaving vascular strands Sometimes a portion intact. White fungal growth of the plant above the may appear on the stalk ear blanches and dies surface. Minute, dark prematurely (top dieback). bodies embedded just Usually, the entire plant under the stalk surface are is killed and several difficult to remove.nodes are rotted. Late in the season, a shiny blackdiscoloration develops in blotches or streaks on thestalk surface, especially on lower internodes. Internalstalk tissue may become black and soft, starting atthe nodes. Lodging typically occurs higher on the 28
  • Fusarium Stalk Rot (Stage III) temperatures resulting in darker pigmentation. Rotting of roots, crown, The role of this root rot in stalk lodging is not fully and lower internodes leads understood. to premature ripening and stalk breakage. Split EAR AND KERNEL ROTS stalks may show whitish- These rots can affect ears, kernels, or cobs, pink to salmon color. reducing test weight and grain quality. Some rots Disintegration starts at the are responsible for development of mycotoxins that nodes. may contaminate grain. Positive identification is Healthy stalk, left. Diseased difficult. Rotting observed in the field is often due to a stalk, right. complex of causal organisms, not just one.Gibberella Stalk Rot (Stage III) Most ear rots are favored by late-season humidity. Affected plants wilt, leaves Infections are increased by ear damage by birds or turn dull gray-green, and insects and by stalk lodging that allows ears to come the lower stalk softens and into contact with the soil. becomes straw colored as plants die. Pith tissue Aspergillus Ear and Kernel Rot (Stage III) disintegrates, leaving only Greenish or yellowish- vascular strands. The tan discoloration occurs inside of a rotted stalk is on and between kernels, pink to red. Small, dark especially near the ear bodies are superficial on tip. Symptoms are morethe lower stalk surface and can be scraped off easily. prevalent if the husk does not cover the ear tip. ThePythium Stalk Rot (Stage II, III) rot is favored by hot, dry This organism attacks weather. It may produce individual plants in localized aflatoxins. areas, sometimes before Cladosporium Ear Rot (Stage III) flowering. It is usually confined to the first internode above Dark gray to greenish the soil line, where rind and black fungal growth pith develop wet rot. Stalks causes kernels to appear twist and collapse. Hot, wet blotched or streaked. Initial weather favors development discoloration appears where kernels are attached to the of this stalk rot. cob. Infection eventuallyRed Root Rot (Stage III) progresses upwards and Red root rot often occurs in plants that are also stalk rotted. Seminal roots infected kernels can are most damaged and be seen scattered over adventitious root damage the ear. If completely increases with their age. colonized, ears are dark The root color of affected and lightweight. This plants ranges from pink to disease is often associated royal red, with higher soil with damage due to insects, hail, or frost.29 Corn Diagnostic Guide
  • Diplodia (Stenocarpella) Ear Rot (Stage III) Penicillium Ear Rot (Stage III) Symptoms include Powdery green to blue- bleached husks, white green mold develops on mold over kernels, and and between kernels. rotted ears with tightly Infection usually begins at adhering husks. Early the ear tips and primarily infection (2 to 4 weeks occurs on ears with after silking) is likely to lead mechanical or insect to complete ear rotting. damage. Infected kernels Later infections may result may become bleached in partial rotting, usually and streaked. “Blue eye”beginning at the base. Since corn is the only known occurs when the embryo becomes discolored duehost, this disease is most severe when corn is to the presence of blue-green fungal spores andplanted following corn in reduced tillage situations. can occur if infected grain is stored at high moisture levels.Fusarium Kernel or Ear Rot (Stage III) Trichoderma Ear Rot (Stage III) Dark green fungal growth is found on and between kernels and husks, often covering the entire ear. Scattered individual or The disease usually occurs groups of kernels show on ears with mechanical or whitish-pink to lavender insect damage. Infected fungal growth. Infected plants tend to be widely kernels may also have distributed within a field. a “starburst” pattern of white streaks on the cap of the kernel or along the base. Infections are more Photo Citations: frequent on damaged ear Clemson University - USDA Cooperative Extension Slidetips, and are favored by dry weather. Fusarium rot Series, Bugwood.org (viewed 9/22/10); Corn Stuntmay produce mycotoxins. 1235014 William M. Brown Jr., Bugwood.org (viewed 9//22/10)Gibberella Ear Rot (Stage III) High Plains Virus 5366657 Symptoms include reddish Howard F. Schwartz, Colorado State University, Bugwood. kernel discoloration, org (viewed 9/22/10) Bacterial Stalk Rot 5361254 usually beginning at the Holcus spot and Pythium stalk rot photos courtesy of Don ear tip. Husks may rot and White at University of Illinois be cemented to the ear. The organism is favored by cool, humid weather, particularly 2 to 3 weeks after silking. It produces several mycotoxins. 30
  • 6 Insect Identification, Injury Symptoms, & Management RecommendationsOnly the most common or the most economically –damaging corn insects in the North American region arediscussed in this chapter. Most, but not all, insect identifications can be made in the field by trained individuals.As insects progress through their life cycles, they change form and features. The following commentsdescribe the appearance of damaging stages, which may not correspond with their appearance whendamage is being investigated. It is not uncommon to investigate crop insect damage, but find none ofthe suspected insects. At other times, damage from insect feeding may be detected, but the insect is nolonger present.Use economic thresholds whenever possible and seek further pest management guidance if symptomsare unclear. Generalized thresholds for most pests are provided in this guide. These thresholds maychange depending on the cost of a control tactic or the commodity value. Always confirm that pestnumbers have been suppressed below thresholds following the application of a rescue tactic. Pesticidesmay perform below expectation due to environmental, chemical, or biological situations, or due toapplication timing.While this publication is focused on in-season diagnostics and treatment options of insect pests of corn,a number of Bt traits are available for several of the insect pests discussed in this handbook. The CornInsect Control with Monsanto Corn Insect Traits and Seed Treatments table (see pp. 39) provides a list ofsome of these products as well as the insects they control. These products provide season-long controlof the specific insects and reduce the need for additional pest management action.APHIDS tassel. Aphid infestations after 50% pollen shed have little effect on grain yield. A rescue application of(1) Corn Leaf Aphid insecticide may be warranted if 50% or more plants This small, soft-bodied, have light to moderate infestations and the crop is bluish-green to gray insect under moisture stress. colonizes on or in the whorl, upper leaves, and (2) Corn Root Aphid tassel, especially under This pinhead-sized, soft-bodied, blue-green to gray- dry conditions. It sucks green insect, may be winged or wingless. Corn root plant juices and can cause aphid groups are found in clusters on the crown and wilting, pollen shed failure, along the roots of young plants. They suck plant juices and barrenness. The and cause wilting, discoloration, and stunting. Cornfield aphid secretes a sticky ants are generally found in conjunction with corn roothoneydew that may gather dirt and act as a medium aphid colonies. There are no rescue treatments for cornfor mold. Predatory insects, like the lady beetle, may root aphid. Cultural practices like crop rotation andbe present and are important predators of aphids. tillage can be effective preventative tactics.Scouting should occur during late whorl to early31 Corn Diagnostic Guide
  • ARMYWORMS or below ground level. This feeding can damage the growing point and cause plants to be bent, twistedFall Armyworm or stunted and sometimes die. Billbug incidence is The fall armyworm grows often associated with nutsedge. Consider spraying up to 1.5 inches long and for billbug if stand loss during seedling stages appears greenish-brown in exceeds 5%. color with an inverted white “Y” on its head. It chews CEREAL LEAF BEETLE ragged holes in the leaves The adult is a 0.2 inch long, hard-shelled beetle and usually concentrates in with metallic blue-black head and wing covers, and the whorl of young plants. reddish- orange legs and thorax. Feeding on corn isThe fall armyworm also feeds on the tassel and bores rare and usually limited to field borders. Though theinto developing ears. Early detection is critical since beetle eats completely through the leaf between thethis pest feeds in protected areas of the plant. It lays veins, plants normally outgrow the injury and rescueround, gray eggs in clusters of 50 or more, which applications are not necessary. Generally infestationsare usually covered with scales. Eggs hatch in 3 to are limited to Michigan, Indiana, and eastward.5 days and larvae migrate to the whorl and adjacentplants. Consider using a rescue application if eggs CHINCH BUGare present on at least 5% of plants or whorl injury The adult is 0.25 inchis detected on 25% or more plants. Because larvae long, and is red and blackfeed deep in the whorl of young plants, control with with white wing covers.insecticides can be difficult. When crushed, this bug(2) True Armyworm emits a distinct odor. It migrates from grasses The true armyworm is and maturing small grains, greenish-gray with orange attacks field borders first or pinkish lines along the and is most destructive body. “Armies” migrate during dry years. The from maturing small grains young nymph (juvenile stage) is bright red, but or grass at night. They turns black as it develops. Chinch bugs cluster in devour foliage, sometimes groups behind the sheath of lower leaves, sucking leaving only leaf midveins, 5364223 plant juices and causing wilting and eventual plantand chew silks. Infestations are more frequent in no-till death. Management may be necessary if 10 or moreor reduced tillage systems and the true armyworm chinch bugs are found on more than 50% of plants.is usually only an occasional pest in rotated corn. Insecticide applications may be limited to only theConsider an insecticide application if 35% or more infested area.plants in the field are infested.BILLBUG COMMON STALK BORER This purplish-brown This black or gray hard- larva may reach 2 inches shelled snout beetle is in length. It has white active only at night. Leaves longitudinal stripes with are punctured while still a distinct purple saddle rolled in the whorl. When near the middle of the they unfurl, irregular rows body. It tends to move of holes appear across the out of weedy or grassy leaves. The billbug also field borders and attack UGA1234011 chews into plant stems at 32
  • corn on field edges (or throughout no-till fields). The instars tunnel in the stalk.larva tunnels into stalks or whorls. Infestation of The second generationplants at the 4-7 leaf stage can lead to dead heart. larvae feed on developingWhorl feeding results in leaves that have a ragged ear tissue, bore intoappearance with injury appearing as a series of holes the shank and ear, andacross the leaf. Timing insecticide applications prior tunnel in the stalk belowto borer tunneling is critical. Consider treating if 10% the ear zone. In the fall,of V2 plants, 15% of V4 plants, or 30% of V6 plants overwintering larvae migrateshow symptoms. to the base of the stalk and prepare overwinteringCORN BORER tunnels in the stalk below soil level. These larvae girdle the plants near the soil level, resulting in severe(1) European Corn Borer stalk lodging. Treatment may be necessary for first This larvae varies in shades generation populations when greater than 35% of of tannish-gray and ranges plants hold larvae or show symptoms. Insecticide in size from less than 0.5 applications for both first and second generations to 1.0 inch long. There are must be applied before they begin tunneling. Consider a rescue treatment for second generation if eggs or young larvae are found on 20 to 25% of plants. CORN EARWORM This larva varies in color from green, yellow, brown to pink, but all have atwo or more generations yellow-brown head andper season. Larvae of reach full size at about 1.5the first generation feed inches. Since the insect ison leaves before they cannibalistic, two or moreburrow into the stalk. This feeding causes broken full-size larvaemidribs and creates a “shot hole” appearance as are seldomleaves grow out of the whorl. Consider treating first found together.generation populations if the moth flight has alreadypeaked and 5% or more of plants have shot holefeeding. Second generation larvae feed on and bore They may feed oninto stalks, tassels, ear shanks, and ear tips causing leaves in the whorl,top breakage, ear drop (with husk attached), stalk on the tassel orlodging, and kernel damage. Treatment for second on silks, but thegeneration larvae may be necessary if more than preferred feeding10% of plants have fresh or hatched egg masses, site is ear tips andor young larvae in the leaf axils. Timing insecticide on developingapplications prior to insect tunneling is critical. kernels. Moreover,(2) Southwestern Corn Borer ear injury often leads to ear molds and rots. The window for effective treatment is the few days afterThis larvae is white or cream-colored and 0.5 to 1.0 eggs are laid and before larvae tunnel into the silkinch long. It has distinct black spots except on the channel.overwintering form. Two generations feed on corn.The first feeds on leaves and creates a “shot hole”effect or “dead heart” in very young plants. Later33 Corn Diagnostic Guide
  • CORN ROOTWORM (2) Northern Corn Rootworm This small, white larva The adult beetle is less feeds on and tunnels than 0.5 inch long, tan or into roots or crowns of young plants. It destroys root systems, can delay development, and causes root lodging. Lodging is accentuated by wind storms. Plants may “gooseneck” across rowsand resume upright growth. Rescue treatments green to greenish-yellowfor control of corn rootworm larvae are available, without distinctive spotsbut efficacy is greatly dependent on the product’s or stripes.ability to move into the root zone. Continuous corn (3) Southern Corn Rootworm or observations of adult beetles The adult beetle is 0.25 made the to 0.5 inch long, yellow previous year or greenish with six black can trigger the spots on each wing cover. use of control (4) Western Corn tactics. The Rootworm adult beetle may feed on corn leaves, stripping spots Corn rootworm feeding The adult beetle is about of the uppersurface away. After pollen shed, it feeds on pollen 0.25 inch long, black andand fresh silks. Heavy silk feeding can reduce orprevent pollination and result in partial or completefailure of kernel set. The beetle can be found in eartips as maturity approaches. The general guidelinefor silk clipping insects is as follows: control may be yellow striped ornecessary if silks are clipped to less than 0.5 inch black with a yellowand fewer than 50% of plants have been pollinated. tip on the wing cover.Also, one beetle per plant in late summer is a useful It cannot be visuallyguideline for justifying whether a control tactic may be identified as tonecessary to prevent larval injury in continuous corn. species.(1) Mexican Corn CUTWORMRootworm There are many species of cutworms that attackThe adult beetle is light corn and other crops such as cotton, tobacco,green and looks similar and many vegetable crops. Cutworms are widelyto the northern corn distributed; some species migrate to Corn Belt statesrootworm beetle, but can from the South and many overwinter there. Youngbe distinguished by a larvae typically feed on leaf margins and larger larvaeblack stripe on the leg. feed below or at the soil surface. They chew into or 34
  • completely cut young stalks, causing wilting or death. (3) Other CutwormsPlants may recover if injury is limited to above the The bronzed, claybacked, dingy, glassy, sandhill, andgrowing point. Cutworms are primarily active at night. variegated cutworms are less frequent pests and lessAn insecticide application should be considered if 2 injurious to corn.to 3% of seedling plants are wilted or cut and larvaeare early in their development (<0.75 inch). If larvae FLEA BEETLEare larger, increase the economic threshold to 5% of The flea beetle is a tiny,plants wilted or cut. Plants at V5 or later stages of shiny, black beetle thatdevelopment usually are unaffected by cutworms. jumps like a grasshopper when disturbed. It feeds(1) Black Cutworm on leaves of young plants The black cutworm larva and produces “scratch varies from almost black to marks” or small holes. The lighter gray and is a pest of flea beetle is the primary many crops at the seedling vector of the bacterium stage. Most of the Corn that causes bacterial Belt is re-colonized each (Stewart’s) wilt of corn. Consider treating field corn year with migrant adults. if five or more beetles per plant are found on V4 Cutting is usually observed or younger corn and adverse growing conditions 300 degree days (base have slowed corn growth. Current seed treatments 50°F) after heavy adult generally provide good control.activity. Several generations per year are possible,but the first generation in spring is most injurious. GRAPE COLASPISAreas of high soil moisture or low-lying areas within a This white, curved, grub-field are most favorable for this insect and should be like larva develops sixscouted first. distinct foreleg projections. It feeds on young corn(2) Western Bean Cutworm roots and can cause The western bean cutworm nutrient deficiency affects corn during symptoms. reproductive stages. The young larva has a pale body with longitudinal brown stripes along the back. Fully grown, it is light brown to GRASSHOPPER Several species of grasshoppers attack corn. The grasshopperpale gray with a brown generally moves fromhead. The cutworm feeds field-side hatching sites.on silks and chews into It eats leaves from thehusks and developing margin inward and may UGA4709020ear tips of the ear shank. prevent pollination by clipping silks. The grasshopperSevere ear and kernel may also chew on tassels, husks, stalks, or kernels.damage can lead to mold Defoliation and ear damage should be used toand ear rots. This insect has historically been limited to determine if an insecticide treatment is necessarythe western Great Plains, but has moved eastward and in field corn. It may be more economical to limitcan now be found in many areas of the Corn Belt. applications to infested areas like field margins.35 Corn Diagnostic Guide
  • JAPANESE BEETLE cream colored spots on wing This shiny, green-bodied covers. It frequently inhabits adult beetle has copper- ear tips as corn approaches to bronze- colored wing maturity and often appears covers. As an adult, it where primary insect pests grows to about 0.5 inch or birds have damaged ear in length and feeds on tips. corn leaves and silks. Leaf feeding by this pest appears skeletonized or SEED CORN BEETLE “lacy.” Larvae are white This small, 0.25 to 0.33 inch long brown groundwith a brown head and feed unobtrusively on the beetle damages the germ and hollows seed beforeroots of plants. They can be differentiated from it germinates. The beetle also attacks emergingother white grubs by the V-shaped pattern of bristles seedlings, causing spotty stands. Damage is greateston the raster. The general guideline for silk clipping if germination has been delayed by the environment.insects, such as an adult Japanese beetle, is as Current seed treatments generally provide good control.follows: control may be necessary if silks are clippedto less than 0.5 inch and fewer than 50% of plantshave been pollinated. SEED CORN MAGGOT This yellowish-whiteLEAF MINER spindle-shaped larva, is This small, white larva or about 0.25 inch long and maggot tunnels between may eat the entire kernel leaf surfaces, leaving before it germinates. Often long blotchy tunnels times it leaves only the within the leaf. This pest seed coat behind. Wet, seldom reaches economic cold, and heavy soils are proportion in corn. associated with this pest that can create spotty, uneven stands. Modern seed treatment provides good control. Otherwise, there is no rescue treatment for seed corn maggot and replanting may be the only option.LESSER CORNSTALK BORER This black larva with white SLUG bands burrows into the This soft-bodied, slimy and stalk base of young plants. legless grayish creature This borer causes wilting hides under residue. It is and plant deformities like active at night and leaves a twisted, bent or often telltale silver-colored slime barren plants. trail on the soil surface. It feeds using a rasping UGA2511032 action on the lower stalk and leaves of youngPICNIC BEETLE plants. This feeding often(Sap Beetle, Scavenger Beetle) removes only one surface of a leaf and the symptom is more common in no-till systems. Insecticidal baitsThis small, dark beetle usually has four orange or are available for slug control, however, injury seldom warrants this expense. 36
  • SOUTHERN CORN LEAF BEETLE due to reduced earAdult beetles are dark brown and can be difficult to weight. The sugarcanefind in the field because they are often covered with borer is found in Florida,soil. Beetles feed on stems and on the edges of Louisiana, Mississippi,leaves of seedlings. Injured plants appear ragged. and Texas.When beetles feed in large numbers, plants may die.This beetle is most problematic in fields that have notbeen cultivated.SPIDER MITE THRIPS Two species can cause Several species of this tiny, slender insect severe damage to corn: occasionally feed on leaves of young corn plants. As banks grass mite and an adult, it develops wings. With mouthparts fitted two-spotted spider mite. for rasping and sucking, thrips remove the green Spider mite problems surface layer in tiny streaks. Individual leaves have a are more prevalent when speckled appearance and fields, or affected areas, temperatures are high and may look silvery. humidity and rainfall are low. The tiny (about the WEBWORM size of a pencil dot), eight- The garden webworm and sod webworm attacklegged creature feeds by piercing individual leaf cells young corn. It appears as a gray to yellow-green,and sucking out the contents. Damage is usually first spotted, bristly larva about 1 inch long. This pestnoted as plants approach tasseling and continues gets its name from the fine web it spins from its silk-through grain dent stage. Lower leaves appear lined underground nest. The larva uses this web toblotched and chlorotic and continued feeding can travel to plants at night and return to its nest duringcause leaves to die. Damage symptoms progress up the day. Similar to the cutworm and wireworm,the plant with time. The mite spins a white web on the webworm’s primary feeding site is at or justthe leaf surface where it feeds. below the surface. Injury becomes more obvious as damaged leaves emerge from the whorl. Larvae alsoSTINK BUG feed on the underside of lower leaves. Several species of green or brown stink bugs WHEAT CURL MITE occasionally attack corn. (Kernel Red Streak) The adult (shield bug) has Kernel red streak is caused a hard, angular back and by a toxin secreted during wing covers, and gives off feeding of the wheat curl a foul odor if crushed. It mite. It is most common on inserts its piercing-sucking yellow corn, but may occur mouthparts into the base on sweet corn, popcorn, of young plants and can kill and white corn. Streaksthe growing point or distort further growth. are more pronounced toward ear tips, especiallySUGARCANE BORER if kernels are exposed.This tan larvae has indistinct brown spots on each Streaks vary from dark red on yellow kernels to pinksegment. It feeds in whorl-and reproductive-stage on white kernels. No detrimental effects from theplants similar to the southwestern corn borer, except discoloration are known.that it does not girdle the stalk. Yield losses occur37 Corn Diagnostic Guide
  • WHITE GRUB Damage to seed or young plants reduces stand The larva has a and vigor. It damages the thick, soft body with germ, stunts plants by three pairs of legs root pruning or kills the just behind a brown growing point by boring head. It ranges from into the base of the stem 0.125 to 1.5 inches near ground level. Modern long depending seed treatments prevent on age, and it damage to seeds. Like characteristically grubs, there is no way to combat this pest after curls into a “C”- stands have been thinned. Use percent stand loss asshape when disturbed. There are several species a gauge for determining if replanting is worthwhile.with 1 to 4 year life cycles. The white grub feedson developing roots of young plants, and causes Photo Citations:stunting, nutrient deficiency symptoms and death. Frank Peairs, Colorado State University, Bugwood.org (viewedHeaviest infestations occur where corn is planted 9/23/10) Armyworm 5364223into killed sod. There are no rescue treatments for Clemson University - USDA Cooperative Extension Slide Series,grubs and the percent stand loss is the best gauge Bugwood.org (viewed 9/23/10) Billbug 1234011for determining if replanting is worthwhile. University of Georgia Archive, University of Georgia, Bugwood. org (viewed 3/11/2011) Grasshopper 4709020WIREWORM David Riley, University of Georgia, Bugwood.org (viewedThe larva is shiny and slender with a yellow- to 9/23/10) Lesser Cornstalk Borer 2511032brown-colored hard body. It ranges in size from 0.5to 1.5 inches long, depending on age and species. Alton N. Sparks, Jr., University of Georgia, Bugwood.org (viewed 3/11/2011) White grub (scarab) 1327103 Corn earworm damage 38
  • Corn Insect Control with Monsanto Corn Insect Traitsand Seed Treatments Protection for Protection for Above and Below Ground Pests Above Ground Pests Genuity® Genuity® VT YieldGard VT Genuity® VT Trait Name SmartStax® Triple PRO™ Triple® Double PRO™ Trait Logo Seed Treatment Poncho® 250 Insects European corn borer Trait Trait Trait Trait Southwestern corn borer Trait Trait Trait Trait Corn earworm (ear feeding) Trait Trait Trait Trait Western bean cutworm Trait NC NC NC Black cutworm Trait/250 Rate 250 Rate 250 Rate 250 RateAbove Ground Fall armyworm Trait Trait Trait Trait Sugarcane borer Trait Trait Trait Trait Common stalk borer Trait Trait Trait Trait Lesser cornstalk borer Trait Trait Trait Trait Corn flea beetle (seedling stage) 250 Rate 250 Rate 250 Rate 250 Rate Corn leaf aphid (seedling stage) 250 Rate 250 Rate 250 Rate 250 Rate Chinch bugs (seedling stage) 250 Rate 250 Rate 250 Rate 250 Rate Southern corn leaf beetle 250 Rate 250 Rate 250 Rate 250 Rate (seedling stage) Western corn rootworm larvae Trait Trait Trait NC Northern corn rootworm larvae Trait Trait Trait NCBelow Ground Mexican corn rootworm larvae Trait Trait Trait NC Wireworm (seedling stage) 250 Rate 250 Rate 250 Rate 250 Rate White grubs (seedling stage) 250 Rate 250 Rate 250 Rate 250 Rate Grape colaspis (seedling stage) 250 Rate 250 Rate 250 Rate 250 Rate Seedcorn maggot (seedling stage) 250 Rate 250 Rate 250 Rate 250 Rate Color Key to Activity Insect activity conferred by: = Control Trait, Insecticide 250 rate, or multiple = Suppression Trait, Insecticide 250 rate, or multiple = No Control NC = No Control39 Corn Diagnostic Guide
  • 7 Herbicide Injury SymptomsMost observed herbicide damage is due to misapplication, but hybrid and environment interactions willsometimes cause injury symptoms to appear. Herbicides used to control weeds in the previous cropmust be taken into consideration, as some herbicide carryover may affect the following corn crop.Various tankmixes of herbicides are widely used. Be alert to plant injury that can be caused by individualtankmix components or by an interaction involving two or more components in the tankmix itself.Corn plants frequently outgrow the effects of herbicide injury and their final yields may not be noticeablylowered.ACCase Inhibitors These herbicides alter theAryloxyphenoxy Propionic Acids and function of the acetolactate synthase (ALS) enzymeCyclohexanediones and affect root and shoot(Including Assure® II, Fusion®, Poast® and Select Max®) growth and development. Symptoms of damage from Corn injury typically acetyl coA carboxylase shows up as reduced root inhibitors include chlorosis systems, often described (yellowing) of newly formed as “bottle-brush” roots. leaves with possible Roots often grow flat or reddening or purpling of parallel to the soil surface and may older leaves. Tissues at turn brown. Stems and midribs can the growing point turn purple, and the stem will be short brown and eventually and thick below the whorl. Mid– to decompose, a symptom late-season symptoms include shortcalled deadheart. Sublethal doses result in pale white internodes, malformed leaves, poorto yellow streaks between leaf veins. root systems, and pinched ears.ALS Inhibitors Herbicides with sulfonylureaImidazolinones, Sulfonylureas, and chemistry are labeled for use onTriazolopyrimidines both corn and soybeans. Products(Including Accent Gold®, Beacon®, Classic®, FirstRate®, in this family may persist in the soil,Lightning®, Pursuit®, and Scepter®) particularly if soil pH is above 6.8 and post-application rainfall has been limited. Though they have the same general chemistry, different herbicides are used on corn and soybeans, and injury of corn may develop the season following sulfonylurea herbicide application to soybean fields. 40
  • Synthetic Auxins Cell Division InhibitorsBenzoic Acids, Phenoxys, and Pyridine AmidesCarboxylic Acids (Including Degree®, Dual II Magnum®, and Harness®)(Including Banvel , Butyrac , Clarity , and Crossbow ) ® ® ® ® Amides (also known as These herbicides, also acetanilides, acetamides, known as plant growth or chloroacetamides) regulators, are translocated are meristematic to meristematic tissue growth inhibitors that and interfere with cell are translocated to formation resulting in the shoot and leaves. abnormal root and shoot These products can cause seedlings to leaf underground or trap seedling leaves so they cannot unfurl, giving a laddergrowth. Symptoms effect. Damage is more likely to take place withinclude twisted whorls cool, wet weather occurring immediately beforeor buggy-whipping emergence.where the leaves do notunfurl, abnormal brace EPSP Synthase Inhibitorsroots, root proliferation, Glycinesbrittle stalks, and poor (Including Roundup® agricultural herbicides andpollination. Growing generic formulations of glyphosate)conditions are a factor in damage expression. These non-selective foliar-applied herbicidesAuxin Transport Inhibitors are translocated andSemicarbazones interfere with amino(Including Distinct®and Status®)These herbicides are primarily active againstbroadleaf plants, but injury symptoms may occurin corn under certain conditions. Injury is similar togrowth regulator herbicides. acid synthesis. If sprayCarotenoid Synthesis Inhibitors drift reaches corn, leavesIsoxazolidinones wilt, turn brown, and die.(Including Command®) Sublethal rates can cause Shallow planting or stress phenoxy-like symptoms. Glyphosate applications conditions that slow that occur too late to corn with Roundup Ready® 2 seedling metabolism can Technology can result in poor kernel set. increase the potential for injury. Damage to corn Glutamine Synthase seedlings the season Inhibitors following an application Phosphinic Acids may occur, especially if soil (Including Ignite® and Liberty®) pH is below 6.0. Affected Inhibitors of glutamine plants are distinctly white synthase are nonspecific andor bleached. Most corn plants recover and new will kill plants that have notleaves have normal color. been modified to express41 Corn Diagnostic Guide
  • resistance to them. Symptomology will range from injury. Drift injury can occurlight speckling on leaves and yellowing to plant if application takes placedeath, depending on the degree and intensity of drift under windy conditions.or spray contamination. Symptoms range from leaf speckling to browning4-HPPD Inhibitors and death of entire leaves.Isoxazoles and Triketones If enough plant tissue is(Including Balance®, Balance® Pro, Callisto®, and Impact®) affected, the plant may wilt Injury symptoms range and die. from minor yellowing, The season following through completely application in soybeans, non-degraded herbicide bleached plants, to residue can cause interveinal bleaching and discoloration of corn seedlings if post-application rainfall was unusually low. Photosystem I Electron Diversion Bipyridiliumssignificant stand loss. (Including Gramoxone Inteon™)Shallow planting or stress Drift of these non-selective contact herbicides mayconditions that slow cause leaf spotting. Symptoms can be confused withseedling metabolism can disease; however, the dead leaf areas will not spread.increase the potentialfor injury. New tissue development should not be Photosystem II Inhibitors—mobileaffected and the effect of injury on yield potential will within plantvary from field to field. Triazines and Ureas (Including atrazine, AAtrex®, Princep®, Sencor®Microtubule Inhibitors and Lorox®)Dinitroanilines These chemical families inhibit photosynthesis, which(Including Prowl® and Treflan®) leads to leaf yellowing, browning, and death, usually Dinitroanilines function by starting at the leaf margins and tip. New leaves may be inhibiting root and shoot symptom-free. Symptoms are more common on sandy growth. Injury can occur soil where an excessive rate was applied. Unfavorable due to carryover from growing conditions may accentuate plant injury. an application made the previous season. Seedling Photosystem II Inhibitors—nonmobile roots are pruned and within plant clubbed. Stunting and Benzothiadiazoles and Nitriles purplish discoloration (Including Basagran®and Buctril®) may occur above ground. These are contact herbicides that are absorbedSymptoms may be confused with nematode damage. through the foliage. Leaf speckling after foliar application is a common injury symptom.PPO InhibitorsDiphenyl Ethers, Phenylphthalimides,Pyrimidines, and Triazolinones(Including Aim®, Authority®, FlexStar®, Reflex®, andResource®)Herbicide application during hot, humid conditions orbefore a long period of cool weather can result in crop 42
  • Herbicides that may be used or trigger symptomology incorn, grouped by mode of action and class of chemistry. HERBICIDE MODES OF ACTION CLASS OF CHEMISTRY TRADEMARK OWNER Acetyl CoA Carboxylase Inhibitors Aryloxphenoxypropionates Assure II ® ACCase Inhibitor Aryloxyphenoxypropionate E.I. du Pont de Nemours & Co. Fusilade® DX ACCase Inhibitor Aryloxyphenoxypropionate Syngenta Fusion® ACCase Inhibitor + ACCase Inhibitor Aryloxyphenoxypropionate + Syngenta Aryloxyphenoxypropionate Hoelon® ACCase Inhibitor Aryloxyphenoxypropionate Bayer Acetyl CoA Carboxylase Inhibitors Cyclohexanediones Poast ® ACCase Inhibitor Cyclohexanedione BASF Poast Plus® ACCase Inhibitor Cyclohexanedione BASF Select® ACCase Inhibitor Cyclohexanedione Valent USA Corporation Select MAX® ACCase Inhibitor Cyclohexanedione Valent USA Corporation Acetolactate Synthase Inhibitors Imidazolinones Authority ® ALS Inhibitor + PPO Inhibitor Imidazolinone + Triazolinone FMC Corporation Assist Optill™ ALS Inhibitor + PPO Inhibitor Imidazolinone + Pyrimidinedione BASF Lightning® ALS Inhibitor + ALS Inhibitor Imidazolinone + Imidazolinone BASF Pursuit® ALS Inhibitor Imidazolinone BASF Pursuit® Plus ALS Inhibitor + Microtubule Inhibitor Imidazolinone + Dinitroaniline BASF Raptor® ALS Inhibitor Imidazolinone BASF Scepter® ALS Inhibitor Imidazolinone BASF Squadron® ALS Inhibitor + Microtubule Inhibitor Imidazolinone + Dinitroaniline BASF Steel® ALS Inhibitor + ALS Inhibitor + Imidazolinone + Imidazolinone + BASF Microtubule Inhibitor Dinitroaniline Acetolactate Synthase Inhibitors Sulfonylureas Accent ® ALS Inhibitor Sulfonylurea E.I. du Pont de Nemours & Co. Accent Gold® ALS Inhibitor + ALS Inhibitor + Sulfonylurea + Sulfonylurea + E.I. du Pont de Nemours & Co. Triazolopyrimidine + Pyridine Authority® XL ALS Inhibitor + PPO Inhibitor Sulfonylurea + Triazolinone FMC Corporation Beacon® ALS Inhibitor + Auxin Sulfonylurea Syngenta Canopy® ALS Inhibitor Sulfonylurea + Triazine E.I. du Pont de Nemours & Co. Celebrity® PlusALS Inhibitor + PPO Inhibitor Sulfonylurea + Benzoic Acid + BASF ALS Inhibitor + Auxin + Auxin Semicarbazone Classic® Transport Inhibitor Sulfonylurea E.I. du Pont de Nemours & Co. Exceed® ALS Inhibitor Sulfonylurea + Sulfonylurea Syngenta NorthStar® ALS Inhibitor + ALS Inhibitor Sulfonylurea + Benzoic Acid Syngenta Option® ALS Inhibitor Sulfonylurea Bayer Peak® ALS Inhibitor + Auxin Sulfonylurea Syngenta Permit® ALS Inhibitor Sulfonylurea Nissan Chemical Industries, Ltd Realm™ Q ALS Inhibitor + 4-HPPD Inhibitor Sulfonylurea + Triketone E.I. du Pont de Nemours & Co. Resolve® Q ALS Inhibitor + ALS Inhibitor Sulfonylurea + Sulfonylurea E.I. du Pont de Nemours & Co. Spirit® ALS Inhibitor + ALS Inhibitor Sulfonylurea + Sulfonylurea Syngenta Steadfast® ALS Inhibitor + ALS Inhibitor Sulfonylurea + Sulfonylurea E.I. du Pont de Nemours & Co. Steadfast® ATZ ALS Inhibitor + ALS Inhibitor + PS II Sulfonylurea + Sulfonylurea + Triazine E.I. du Pont de Nemours & Co. Inhibitor Synchrony® XP ALS Inhibitor + ALS Inhibitor Sulfonylurea + Sulfonylurea E.I. du Pont de Nemours & Co. Valor® XLT PPO Inhibitor + ALS Inhibitorr Phenylphthalimide + Sulfonylurea Valent USA Corporation Yukon® ALS Inhibitor + Auxin Benzoic Acid + Sulfonylurea Nissan Chemical Industries, Ltd.Herbicides shown in bold type contain two or more active ingredients, so they may appear in more than one section of the table.43 Corn Diagnostic Guide
  • HERBICIDE MODES OF ACTION CLASS OF CHEMISTRY TRADEMARK OWNER Acetolactate Synthase Inhibitors Triazolopyrimidines Accent Gold® ALS Inhibitor + ALS Inhibitor + ALS Pyridine + Sulfonylurea + E.I. du Pont de Nemours & Co. Inhibitor + Auxin Sulfonylurea + Triazolopyrimidine Authority™ First ALS Inhibitor + PPO Inhibitor Triazolopyrimidine + Triazolinone FMC Corporation Broadstrike™ ALS Inhibitor Triazolopyrimidine Dow AgroSciences LLC FirstRate® ALS Inhibitor Triazolopyrimidine Dow AgroSciences LLC Gangster® ALS Inhibitor + PPO Inhibitor Triazolopyrimidine + Valent USA Corporation Phenylphthalimide Gauntlet® ALS Inhibitor + PPO Inhibitor Triazolopyrimidine FMC Corporation Hornet® ALS Inhibitor + Auxin Triazolopyrimidine + Triazolinone Dow AgroSciences LLC Python® ALS Inhibitor Triazolopyrimidine + Pyridine Dow AgroSciences LLC SureStart™ ALS Inhibitor + Auxin + Cell Division Triazolopyrimidine Dow AgroSciences LLC Inhibitor Triazolopyrimidine + Pyridine + TripleFLEX™ Cell Division Inhibitor + Auxin + ALS Amide + Pyridine + Herbicide Inhibitor Triazolopyrimidine Monsanto Technology LLC Synthetic Auxins Benzoic Acids Banvel® Auxin Benzoic Acid BASF Celebrity® Plus ALS Inhibitor + Auxin + Auxin Sulfonylurea + Benzoic Acid + BASF Transport Inhibitor Semicarbazone Clarity® Auxin Benzoic Acid BASF Distinct® Auxin + Auxin Transport Inhibitor Benzoic Acid + Semicarbazone BASF Marksman® Auxin + PS II Inhibitor Benzoic Acid + Triazine BASF NorthStar® ALS Inhibitor + Auxin Sulfonylurea + Benzoic Acid Syngenta Status® Auxin + Auxin + Transport Inhibitor Benzoic Acid + Semicarbazone BASF Yukon® ALS Inhibitor + Auxin Benzoic Acid + Sulfonylurea Nissan Chemical Industries, Ltd. Synthetic Auxins Phenoxy Carboxylic Acids 2,4-D Auxin Phenoxy Generic chemical name Butyrac® Auxin Phenoxy Allbaugh, Inc. Crossbow® Auxin + Auxin Phenoxy + Pyridine Dow AgroSciences LLC Synthetic Auxins Pyridine Carboxylic Acids Accent Gold ® ALS Inhibitor + ALS Inhibitor + Pyridine + Sulfonylurea + E.I. du Pont de Nemours & Co. ALS Inhibitor + Auxin Sulfonylurea + Triazolopyrimidine Crossbow® Auxin + Auxin Phenoxy + Pyridine Dow AgroSciences LLC Hornet® ALS Inhibitor + Auxin Triazolopyrimidine + Pyridine Dow AgroSciences LLC. Stinger® Auxin Pyridine Dow AgroSciences LLC SureStart™ ALS Inhibitor + Auxin + Cell Division Triazolopyrimidine + Pyridine + Dow AgroSciences LLC Inhibitor Amide Tordon® Auxin Pyridine Dow AgroSciences LLC Transline® Auxin Pyridine Dow AgroSciences LLC TripleFLEX™ Cell Division Inhibitor + Auxin + ALS Amide + Pyridine + Monsanto Technology LLC Herbicide Inhibitor Triazolopyrimidine WideMatch® Auxin + Auxin Pyridine + Pyridine Dow AgroSciences LLC Auxin Transport Inhibitors Semicarbazones Celebrity® Plus ALS Inhibitor + Auxin + Auxin Sulfonylurea + Benzoic Acid + BASF Transport Inhibitor Semicarbazone Distinct® Auxin + Auxin Transport Inhibitor Benzoic Acid + Semicarbazone BASF Status® Auxin + Auxin + Transport Inhibitor Benzoic Acid + Semicarbazone BASFHerbicides shown in bold type contain two or more active ingredients, so they may appear in more than one section of the table. 44
  • HERBICIDE MODES OF ACTION CLASS OF CHEMISTRY TRADEMARK OWNER Carotenoid Synthesis Inhibitors Isoxazolidinones Command ® Carotenoid Synthesis Inhibitor Isoxazolidinone FMC Corporation Command® Xtra Carotenoid Synthesis Inhibitor + Isoxazolidinone + Triazolinone FMC Coporation PPO Inhibitor Commence® Carotenoid Synthesis Inhibitor + Isoxazolidinone + Triazolinone FMC Coporation Micrutubule Inhibitor Cell Division Inhibitors Amides Axiom ® Cell Division Inhibitor + PS II Inhibitor Amide + Triazine Bayer Define™ Cell Division Inhibitor Amide Bayer Degree® Cell Division Inhibitor Amide Monsanto Technology LLC Degree Xtra ® Cell Division Inhibitor + PS II Inhibitor Amide + Triazine Monsanto Technology LLC Domain™ Cell Division Inhibitor + PS II Inhibitor Amide + Triazine Bayer Dual II Magnum® Cell Division Inhibitor Amide Syngenta Guardsman Max® Cell Division Inhibitor + PS II Inhibitor Amide + Triazine BASF Expert® Cell Division Inhibitor + PS II Inhibitor Amide + Triazine + Glycine Syngenta + EPSPS Inhibitor Halex™ GT Cell Division Inhibitor + 4-HPPD Amide + Triketone + Glycine Syngenta Inhibitor + EPSPS Inhibitor Harness® Cell Division Inhibitor Amide Monsanto Technology LLC Harness® Xtra Cell Division Inhibitor + PS II Inhibitor Amide + Triazine Monsanto Technology LLC Lexar® Cell Division Inhibitor + 4-HPPD Amide + Triketone + Triazine Syngenta Inhibitor + PS II Inhibitor Lumax® Cell Division Inhibitor + 4-HPPD Amide + Triketone + Triazine Syngenta Inhibitor + PS II Inhibitor Micro-Tech® Cell Division Inhibitor Amide Monsanto Technology LLC Outlook® Cell Division Inhibitor Amide BASF Radius™ Cell Division Inhibitor + 4-HPPD Amide + Isoxazole Bayer Inhibitor SureStart™ ALS Inhibitor + Auxin + Cell Division Triazolopyrimidine + Pyridine + Dow AgroSciences LLC Inhibitor Amide TripleFLEX™ Cell Division Inhibitor + Auxin + ALS Amide + Pyridine + Monsanto Technology LLC Herbicide Inhibitor Triazolopyrimidine Verdict™ PPO Inhibitor + Cell Division Inhibitor Pyrimidinedione + Chloroacetamide BASF Warrant™ Cell Division Inhibitor Amide Monsanto Technology LLC Herbicide EPSP Synthase Inhibitors Glycines Expert® Cell Division Inhibitor + PS II Inhibitor Glycine + Triazine Syngenta + EPSPS Inhibitor Flexstar® GT PPO Inhibitor + EPSPS Inhibitor Diphenyl Ether + Glycine Syngenta Glyphomax® EPSPS Inhibitor Glycine Dow AgroSciences LLC Halex™ GT Cell Division Inhibitor + 4-HPPD Amide + Isoxazole + Glycine Syngenta Inhibitor + EPSPS Inhibitor Roundup EPSPS Inhibitor Glycine Monsanto Technology LLC PowerMAX® Roundup EPSPS Inhibitor Glycine Monsanto Technology LLC WeatherMAX® Touchdown® EPSPS Inhibitor Glycine Syngenta Glutamine Synthase Inhibitors Phosphinic Acids Ignite® GS Inhibitor Phosphinic Acid Bayer Liberty® GS Inhibitor Phosphinic Acid Bayer Liberty® ATZ GS Inhibitor + PS II Inhibitor Phosphinic Acid + Triazine BayerHerbicides shown in bold type contain two or more active ingredients, so they may appear in more than one section of the table.45 Corn Diagnostic Guide
  • HERBICIDE MODES OF ACTION CLASS OF CHEMISTRY TRADEMARK OWNER 4-Hydroxyphenyl-Pyruvate-Dioxygenase Isoxazole Inhibitor Balance® 4-HPPD Inhibitor Isoxazole Bayer Balance® Flex 4-HPPD Inhibitor Isoxazole Bayer Balance® Pro 4-HPPD Inhibitor Isoxazole Bayer Corvus™ 4-HPPD Inhibitor Isoxazole Syngenta Laudis™ 4-HPPD Inhibitor Isoxazole Bayer Radius™ Cell Division Inhibitor + 4-HPPD Amide + Isoxazole Bayer Inhibitor 4-Hydroxyphenyl-Pyruvate-Dioxygenase Triketones Inhibitor Callisto® 4-HPPD Inhibitor Triketone Sygenta Halex™ GT Cell Division Inhibitor + 4-HPPD Amide + Triketone + Glycine Sygenta. Inhibitor + EPSPS Inhibitor Impact® 4-HPPD Inhibitor Triketone Amvac Chemical Corporation Lexar® Cell Division Inhibitor + 4-HPPD Triketone Syngenta Inhibitor + PS II Inhibitor Lumax® Cell Division Inhibitor + 4-HPPD Amide + Triketone + Triazine Sygenta Inhibitor + PS II Inhibitor Realm™ Q ALS Inhibitor + 4-HPPD Inhibitor Sulfonylurea + Triketone E.I. du Pont de Nemours & Co. Microtubule Inhibitors Dinitroanilines Commence ® Carotenoid Synthesis Inhibitor + Isoxazolidinone + Dinitroaniline FMC Corporation Micrutubule Inhibitor Pendimax® Micrutubule Inhibitor Dinitroaniline Dow AgroSciences LLC Prowl® Micrutubule Inhibitor Dinitroaniline BASF Prowl® H2O Micrutubule Inhibitor Dinitroaniline BASF Pursuit® Plus ALS Inhibitor + Micrutubule Inhibitor Imidazolinone + Dinitroaniline BASF Sonalan® Micrutubule Inhibitor Dinitroaniline Dow AgroSciences LLC Squadron® ALS Inhibitor + Micrutubule Inhibitor Imidazolinone + Dinitroaniline BASF Steel® ALS Inhibitor + ALS Inhibitor + Imidazolinone + Imidazolinone + BASF Micrutubule Inhibitor Dinitroaniline Treflan® Micrutubule Inhibitor Dinitroaniline Dow AgroSciences LLC trifluralin Micrutubule Inhibitor Dinitroaniline Generic chemical name Protoporphyrinogen Oxidase Inhibitors Diphenyl Ethers Blazer® PPO Inhibitor Diphenyl Ether United Phosphorus, Inc. Cobra® PPO Inhibitor Diphenyl Ether Valent USA Corporation FlexStar® PPO Inhibitor Diphenyl Ether Syngenta Flexstar® GT PPO Inhibitor + EPSPS Inhibitor Diphenyl Ether + Glycine Syngenta Goal® PPO Inhibitor Diphenyl Ether Dow AgroSciences LLC Phoenix™ PPO Inhibitor Diphenyl Ether Valent USA Corporation Reflex® PPO Inhibitor Diphenyl Ether Syngenta Storm® PPO Inhibitor + PS II Inhibitor Diphenyl Ether + Benzothiadiazole United Phosphorus, Inc. Ultra Blazer® PPO Inhibitor Diphenyl Ether United Phosphorus, Inc. Protoporphyrinogen Oxidase Inhibitors Phenylphthalimides Gangster ® ALS Inhibitor + PPO Inhibitor Triazolopyrimidine + Valent USA Corporation Phenylphthalimide Resource® PPO Inhibitor Phenylphthalimide Valent USA Corporation Valor® SX PPO Inhibitor Phenylphthalimide Valent USA Corporation Valor® XLT ALS Inhibitor + PPO Inhibitor Phenylphthalimide + Sulfonylurea Valent USA CorporationHerbicides shown in bold type contain two or more active ingredients, so they may appear in more than one section of the table. 46
  • HERBICIDE MODES OF ACTION CLASS OF CHEMISTRY TRADEMARK OWNER Protoporphyrinogen Oxidase Inhibitors Pyrimidinediones Optill™ ALS Inhibitor + PPO Inhibitor Imidazolinone + Pyrimidinedione BASF Sharpen™ PPO Inhibitor Pyrimidinedione BASF Verdict™ PPO Inhibitor + Cell Division Inhibitor Pyrimidinedione + Chloroacetamide BASF Protoporphyrinogen Oxidase Inhibitors Triazolinones Aim® PPO Inhibitor Triazolinone FMC Corporation Authority® PPO Inhibitor Triazolinone FMC Corporation Authority® Assist ALS Inhibitor + PPO Inhibitor Imidazolinone + Triazolinone FMC Corporation Authority™ First ALS Inhibitor + PPO Inhibitor Triazolopyrimidine + Triazolinone FMC Corporation Authority® XL ALS Inhibitor + PPO Inhibitor Sulfonylurea + Triazolinone FMC Corporation Command® Xtra Carotenoid Synthesis Inhibitor + Isoxazolidinone + Triazolinone FMC Corporation PPO Inhibitor Gauntlet® ALS Inhibitor + PPO Inhibitorr Triazolopyrimidine + Triazolinone FMC Corporation PPO Inhibitor Triazolinone Photosystem I Electron Diversion Bipyridiliums diquat ® PS I Inhibitor Bipyridilium Generic chemical name Reward® PS I Inhibitor Bipyridilium Syngenta Gramoxone PS I Inhibitor Bipyridilium Syngenta Inteon™ Photosystem II Inhibitors Benzothiadiazoles Basagran ® PS II Inhibitor Benzothiadiazole BASF Laddok® PS II Inhibitor + PS II Inhibitor Benzothiadiazole + Triazine BASF Storm® PPO Inhibitor + PS II Inhibitor Diphenyl Ether + Benzothiadiazole United Phosphorus, Inc. Photosystem II Inhibitors Nitriles Bison® PS II Inhibitor Nitrile Winfield Solutions, LLC Buctril® PS II Inhibitor Nitrile Bayer Moxy® PS II Inhibitor Nitrile Winfield Solutions, LLC Photosystem II Inhibitors Triazines Aatrex® PS II Inhibitor Triazine Syngenta atrazine PS II Inhibitor Triazine Generic chemical name Axiom® Cell Division Inhibitor + PS II Inhibitor Amide + Triazinone Bayer Canopy® ALS Inhibitor + PS II Inhibitor Sulfonylurea + Triazine E.I. du Pont de Nemours & Co. Degree Xtra® Cell Division Inhibitor + PS II Inhibitor Amide + Triazine Monsanto Technology LLC Domain™ Cell Division Inhibitor + PS II Inhibitor Amide + Triazine Bayer Guardsman Max® Cell Division Inhibitor + PS II Inhibitor Amide + Triazine BASF Harness® Xtra Cell Division Inhibitor + PS II Inhibitor Amide + Triazine Monsanto Technology LLC Laddok® PS II Inhibitor + PS II Inhibitor Benzothiadiazole + Triazine BASF Lexar® Cell Division Inhibitor + 4-HPPD Amide + Isoxazole + Triazine Syngenta Inhibitor + PS II Inhibitor Liberty® ATZ GS Inhibitor + PS II Inhibitor Phosphonic Acid + Triazine Bayer Lumax® Cell Division Inhibitor + 4-HPPD Amide + Isoxazole + Triazine Syngenta Inhibitor + PS II Inhibitor Marksman® Auxin + PS II Inhibitor Benzoic Acid + Triazine BASF Princep® PS II Inhibitor Triazine Syngenta Sencor® PS II Inhibitor Triazine Bayer Steadfast® ATZ ALS Inhibitor + ALS Inhibitor + Sulfonylurea + Sulfonylurea + E.I. du Pont de Nemours & Co PS II Inhibitor Triazine Photosystem II Inhibitors Ureas Lorox® PS II Inhibitor Urea E.I. du Pont de Nemours & Co.Herbicides shown in bold type contain two or more active ingredients, so they may appear in more than one section of the table.47 Corn Diagnostic Guide
  • Herbicides by Active Ingredientand Mode of Action HERBICIDE ACTIVE INGREDIENT MODE OF ACTION2,4-D 2,4-D AuxinAAtrex® Atrazine PS II InhibitorAccent ® Nicosulfuron ALS Inhibitor Clopyralid + Flumetsulam + Nicosulfuron + ALS Inhibitor + ALS Inhibitor + ALS Inhibitor +Accent Gold® Rimsulfuron AuxinAim® Carfentrazone PPO InhibitorAssure II ® Quizalofop ACCase Inhibitoratrazine Atrazone PS II InhibitorAuthority® Sulfentrazone PPO InhibitorAuthority Assist ® Imazethapyr + Sulfentrazone ALS Inhibitor + PPO InhibitorAuthority First ™ Cloransulam + Sulfentrazone ALS Inhibitor + PPO InhibitorAuthority® XL Chlorimuron + Sulfentrazone ALS Inhibitor + PPO InhibitorAxiom ® Flufenacet + Metribuzin Cell Division Inhibitor + PS II InhibitorBalance ® Isoxaflutole 4-HPPD InhibitorBalance® Flexx Isoxaflutole 4-HPPD InhibitorBalance Pro ® Isoxaflutole 4-HPPD InhibitorBanvel ® Dicamba AuxinBasagran ® Bentazon PS II InhibitorBeacon® Primisulfuron ALS InhibitorBison ® Bromoxynil PS II InhibitorBlazer ® Aciflourfen PPO InhibitorBroadstrike™ Flumetsulam ALS InhibitorBuctril ® Bromoxynil PS II InhibitorButyrac ® 2,4-DB AuxinCallisto® Mesotrione 4-HPPD InhibitorCanopy ® Chlorimuron + Metribuzin ALS Inhibitor + PS II InhibitorCelebrity Plus ® Dicamba + Diflufenzopyr + Nicosulfuron ALS Inhibitor + Auxin + Auxin Transport InhibitorClarity ® Dicamba AuxinClassic® Chlorimuron ALS InhibitorCobra ® Lactofen PPO InhibitorCommand ® Clomazone Carotenoid Synthesis InhibitorCommand® Xtra Clomazone + Sulfentrazone Carotenoid Synthesis Inhibitor + PPO Inhibitor Carotenoid Synthesis Inhibitor + MicrotubuleCommence® Clomazone + Trifluralin InhibitorCorvus™ Isoxaflutole 4-HPPD InhibitorCrossbow ® 2,4-D + Triclopyr Auxin + Auxin 48
  • Herbicides by Active Ingredientand Mode of Action (cont.) HERBICIDE ACTIVE INGREDIENT MODE OF ACTIONDefine™ Flufenacet Cell Division InhibitorDegree® Acetochlor Cell Division InhibitorDegree Xtra ® Acetochlor + Atrazine Cell Division Inhibitor + PS II Inhibitordiquat Diquat PS I InhibitorDistinct® Dicamba + Diflufenzopyr Auxin + Auxin Transport InhibitorDomain ® Flufenacet + Metribuzin Cell Division Inhibitor + PS II InhibitorDual II Magnum ® Metolachlor Cell Division InhibitorExceed® Primisulfuron + Prosulfuron ALS Inhibitor + ALS Inhibitor Cell Division Inhibitor + PS II Inhibitor + EPSPSExpert® Atrazine + Glyphosate + Metolachlor InhibitorFirstRate® Cloransulam ALS InhibitorFlexstar ® Fomesafen PPO InhibitorFusilade DX ® Fluazifop ACCase InhibitorFlexstar® GT Fomesafen + Glyphosate PPO Inhibitor + EPSPS InhibitorFusion ® Fenoxaprop + Fluazifop ACCase Inhibitor + ACCase InhibitorGangster ® Cloransulam + Flumioxazin ALS Inhibitor + PPO InhibitorGauntlet ® Cloransulam + Sulfentrazone ALS Inhibitor + PPO InhibitorGlyphomax® Glyphosate EPSPS InhibitorGoal ® Oxyfluorfen PPO InhibitorGramoxone Inteon™ Paraquat PS I InhibitorGuardsman Max® Atrazine + Dimethenamid Cell Division Inhibitor + PS II Inhibitor Cell Division Inhibitor + 4-HPPD Inhibitor +Halex™ GT Glyphosate + Mesotrione + Metolachlor EPSPS InhibitorHarness® Acetochlor Cell Division InhibitorHarness Xtra ® Acetochlor + Atrazine Cell Division Inhibitor + PS II InhibitorHoelon ® Diclofop ACCase InhibitorHornet® Clopyralid + Flumetsulam ALS Inhibitor + AuxinIgnite ® Glufosinate GS InhibitorImpact ® Topramezone 4-HPPD InhibitorLaddok Atrazine + Bentazon PS II Inhibitor + PS II InhibitorLaudis™ Tembotrione 4-HPPD Inhibitor Cell Division Inhibitor + 4-HPPD Inhibitor + PS IILexar® Atrazine + Mesotrione + Metolachlor InhibitorLiberty® Glufosinate GS InhibitorLiberty ATZ ® Atrazine + Glufosinate GS Inhibitor + PS II InhibitorLightning ® Imazapyr + Imazethapyr ALS Inhibitor + ALS InhibitorLorox® Linuron PS II Inhibitor49 Corn Diagnostic Guide
  • Herbicides by Active Ingredientand Mode of Action (cont.) HERBICIDE ACTIVE INGREDIENT MODE OF ACTION Cell Division Inhibitor + 4-HPPD Inhibitor + PS IILumax® Atrazine + Mesotrione + Metolachlor InhibitorMarksman® Atrazine + Dicamba Auxin + PS II InhibitorMicro-Tech ® Alochlor Cell Division InhibitorMoxy™ Bromoxynil PS II InhibitorNorthStar ® Dicamba + Primisulfuron ALS Inhibitor + AuxinOptill ™ Imazethapyr + Saflufenacil ALS Inhibitor + PPO InhibitorOption® Foramsulfuron ALS InhibitorOutlook ® Dimethenamid Cell Division InhibitorPeak ® Prosulfuron ALS InhibitorPendimax® Pendimethalin Microtubule InhibitorPermit ® Halosulfuron ALS InhibitorPhoenix™ Lactofen PPO InhibitorPoast Plus® Sethoxydim ACCase InhibitorPoast ® Sethoxydim ACCase InhibitorPrincep ® Simazine PS II InhibitorProwl ® Pendimethalin Microtubule InhibitorProwl® H2O Pendimethalin Microtubule InhibitorPursuit ® Imazethapyr ALS InhibitorPursuit Plus ® Imazethapyr + Pendimethalin ALS Inhibitor + Mictrotubule InhibitorPython® Flumetsulam ALS InhibitorRadius™ Flufenacet + Isoxaflutole Cell Division Inhibitor + 4-HPPD InhibitorRaptor ® Imazamox ALS InhibitorRealm™ Q Rimsulfuron + Mesotrione ALS Inhibitor + 4-HPPD InhibitorReflex ® Fomesafen PPO InhibitorResolve Q ® Rimsulfuron + Thifensulfuron ALS Inhibitor + ALS InhibitorResource ® Flumiclorac PPO InhibitorReward® Diquat PS I InhibitorRoundup PowerMAX ® Glyphosate EPSPS InhibitorRoundup Glyphosate EPSPS InhibitorWeatherMAX®Scepter® Imazaquin ALS InhibitorSelect ® Clethodim ACCase InhibitorSelect MAX® Clethodim ACCase InhibitorSencor ® Metribuzin PS II InhibitorSharpen ™ Saflufenacil PPO Inhibitor 50
  • Herbicides by Active Ingredientand Mode of Action (cont.) HERBICIDE ACTIVE INGREDIENT MODE OF ACTIONSonalan® Ethalfluralin Microtubule InhibitorSpirit® Primisulfuron + Prosulfuron ALS Inhibitor + ALS InhibitorSquadron ® Imazaquin + Pendimethalin ALS Inhibitor + Microtubule InhibitorStatus ® Dicamba + Diflufenzopyr Auxin + Auxin Transport InhibitorSteadfast® Nicosulfuron + Rimsulfuron ALS Inhibitor + ALS InhibitorSteadfast ATZ ® Atrazine + Nicosulfuron + Rimsulfuron ALS Inhibitor + ALS Inhibitor + PS II InhibitorSteel ® Imazaquin + Imazethapyr + Pendimethalin ALS Inhibitor + ALS Inhibitor + Microtubule InhibitorStinger® Clopyralid AuxinStorm ® Bentazon PPO Inhibitor + PS II InhibitorSureStart ™ Acetochlor + Clopyralid + Flumetsulam ALS Inhibitor + Auxin + Cell Division InhibitorSureStart™ Acetochlor + Clopyralid + Flumetsulam ALS Inhibitor +Auxin + Cell Division InhibitorSynchrony XP ® Chlorimuron + Thifensulfuron ALS Inhibitor + ALS InhibitorTordon ® Picloram AuxinTouchdown ® Glyphosate EPSPS InhibitorTransline® Clopyralid AuxinTreflan ® Trifluralin Microtubule Inhibitortrifluralin Trifluralin Microtubule InhibitorTripleFLEX™ Herbicide Acetochlor + Clopyralid + Flumetsulam Cell Division Inhibitor + Auxin + ALS InhibitorUltra Blazer ® Acifluorfen PPO InhibitorValor SX ® Flumioxazin PPO InhibitorValor® XLT Flumioxazin + Chlorimuron PPO Inhibitor + ALS InhibitorVerdict ™ Dimethenamid + Saflufenacil PPO Inhibitor + Cell Division InhibitorWarrant Herbicide ™ Acetochlor Cell Division InhibitorWideMatch ® Clorpyralid + Fluroxypyr Auxin + AuxinYukon® Dicamba + Halosulfuron ALS Inhibitor + Auxin51 Corn Diagnostic Guide
  • 9 Nutrient Deficiency SymptomsThis section describes visual symptoms of moderate to severe nutrient deficiencies. These deficienciesare not always due to insufficient nutrient supplies in the soil. Symptoms are often induced by poor rootdevelopment, root damage, unfavorable soil conditions (dry, water-logged, or compacted), or unfavorableweather. Nutrient availability is highly variable, strongly influenced by management decisions, and is onlyone component of soil productivity. Therefore, correction does not automatically require application of thesuspected nutrient.Mobile elements, like nitrogen, may become unavailable to plants because of leaching or gasification.Soil compaction, dry soil, soil where water has ponded, and inadequate rooting are examples of soil andplant conditions that may limit nutrient uptake. Specific nutrient deficiencies can be difficult to diagnoseaccurately. Soil and/or plant analysis may help identify and establish the cause of the symptoms. Withthese analyses be aware of possible nutrient interactions that may influence results.Boron (B) Iron (Fe)Boron deficiency is rare. Irregular white spots occur Iron deficiency symptomsbetween leaf veins and may combine into white are rare. The upper leavesstripes with a raised waxy appearance. Bush-shaped turn white between theplants often fail to produce a tassel or ear. Deficiency veins, affecting the entireis favored by drought, high pH and sandy soil low length. Symptoms arein organic matter. Boron toxicity can cause yellow, favored by high pHdying leaf margins and tips. (alkaline) soil, cool weather, and wet, compacted soil.Calcium (Ca)Symptoms of calcium deficiency are rare. Seedlingleaf tips adhere to the next lower leaf, resultingin laddering effect and failure to unfurl normally. Magnesium (Mg)Deficiency is favored by very low pH (below 5.5) and Yellow-white streakinghigh magnesium or potassium level. occurs between veins of lower leaves if magnesiumCopper (Cu) is deficient. Eventually,Copper deficiency is rare. Young leaves yellow as margins and tips of olderthey emerge from the whorl and may die at the tip leaves become reddish-and edges. Stalks are soft and flexible. Deficiency is purple, then die. Deficiencyfavored by high organic matter soils. is favored by low pH, sandy soil and high potassium levels. 52
  • Manganese (Mn) leaves may be symptom-free. Symptoms are seldom Manganese deficiency is observed on knee-high and larger plants. Ears may rare. The area between be small and misshapen, twisted with one or more leaf veins turns pale green- kernel rows missing on one side. yellow. Stalks are thin and limber. Symptoms are Potassium (K) favored by peat or muck Symptoms of potassium soil, high pH and sandy soil deficiency are seldom seen high in organic matter. before plants are knee- high. Edges of lower leaves turn yellow and die (fire), starting at the tip. LeavesMolybdenum (Mo) may break away. Plants areMolybdenum deficiency is rare. Young leaves shortened. Ears are smallsometimes twist, wilt and die along margins. Older and chaffy with poor tip-fill.leaves die at the tip, along margins and between Deficiency is favored byveins. Deficiency is favored by low pH and strong soil wet or compacted soils, sandy or strongly weatheredweathering. soil, and organic soil. Heavy potassium removal by previous crop can also favor deficiency.Nitrogen (N) Nitrogen-deficient Sulfur (S) plants are spindly, Deficiency of sulfur causes pale and stunted. stunted, slow-growing and Lower leaves yellow plants. Yellowing develop a yellow- occurs between veins, orange color especially of younger in the shape of (upper) leaves. Older plants an inverted “V” rarely show symptoms. beginning at the Symptoms are favored by tip and following cold, wet soil, low pH, andthe midvein. Leaves may begin to die (fire) at the tip. low organic matter.Symptoms advance up the plant to younger leaves.Ears are small and pinched at the tip. Symptoms are Zinc (Zn)favored by cold, ponded, dry, or low organic matter Symptoms of zincsoil, and incorporation of low-nitrogen residues. deficiency are rare beyond the seedling stage. YellowPhosphorus (P) to white bleached bands Leaves of young appear on the lower part of phosphorus- deficient leaves while the midvein, plants are bluish-green and margins and tip remain slightly narrowed, turning green. Newly affected reddish-purple starting leaves are sometimes at the tips and along the described as “white buds.” edges. Leaf tips may die. If The deficiency is favored by high soil phosphorus, conditions for phosphorous high pH, cool, wet soil and low organic matter – such uptake improve, newer as from exposed subsoil.53 Corn Diagnostic Guide
  • Index4-HPPD Inhibitors ........ . . . . . . . . . . 42 Diplodia Stalk Rot ............ . . ...... 28 Phosphorus ................. . . . ....... 53ACCase Inhibitors .................... 40 EPSP Synthase Inhibitors . . . ....... 41 Photosystem I Electron Diversion .. 42Acetanilides . . . . ....................... 41 European Corn Borer .... . . . . ... . . . . 33 Photosystem II Inhibitors - mobile .. 42ALS Inhibitors..........................40 Eyespot ............... . . . . . . . . . ....... 26 Photosystem II Inhibitors - nonmobile .. 42Amides .................................41 Fall Armyworm ...... . . . . . . . . ....... 32 Physoderma Brown Spot . . . . . ...... 26Anthracnose ...........................24 Flea Beetle ................... . . ....... 35 Picnic Beetle ................ . . . ....... 36Anthracnose Stalk Rot ... . . . . . . . .... 28 Fusarium Kernel or Ear Rot ... . . . ... 30 Pinched Ear Syndrome ........... . .. 40Aphids ................................. 31 Fusarium Stalk Rot ..... . . . . . . . . ..... 29 Potassium ................... . . . ....... 53Armyworms ............................32 Gibberella Ear Rot ....... . . . . . . . . . ... 30 PPO Inhibitors .............. . . . ....... 42Aryloxyphenoxy Propionic Acids ... 40 Gibberella Stalk Rot ......... . . . . . ... 29 Pyridine Carboxylic Acids .. . . . ..... 41Aspergillus Ear and Kernel Rot ......29 Glutamine Synthase Inhibitors ...... 41 Pyrimidines . . . . . . . .................... 42Auxin Transport Inhibitors ........... 41 Glycines ....................... . ....... 41 Pythium Stalk Rot .. . . . .............. . 29Bacterial Leaf Blight ................. 24 Goss’s Wilt .................... . ....... 26 Red Root Rot ............... . . . ....... 29Bacterial Stalk Rot ................... 28 Grape Colaspis ... . . . . . . . . . . . . ....... 35 Sap Beetle .................. . . . ....... 36Bacterial Wilt .......................... 24 Grasshopper ........... . . . . . . . . ...... 35 Scavenger Beetle ..................... 36Benzoic Acids .........................41 Gray Leaf Spot ............. . . . ....... 25 Seed Corn Beetle .... . . . . . .... ....... 36Benzothiadiazoles .................... 42 Head Smut ............ . . . . . . . . ....... 26 Seed Corn Maggot .. . . . ............. 36Billbug ... . . . . .......................... 32 Helminthosporium Leaf Spot .. . . . .. 25 Semicarbazones ...... . . . . . . . ....... 41Bipyridiliums .......................... 42 High Plains Virus ........... . . . . . . .... 27 Slug ..................................... 36Black Cutworm ....................... 35 Holcus Spot ............... . . . . ....... 25 Sorghum Downy Mildew ... . . . ...... 28Blister Smut ........................... 26 Imidazolinones ... . . . ........ . . ....... 40 Southern Corn Leaf Blight .. . . . ..... 26Boil Smut .............................. 26 Iron ........................... . . . ....... 52 Southern Corn Rootworm .. . . . . .... 34Boron .................................. 52 Isoxazoles ... . . . ............. . . ....... 42 Southern Corn Rust .................. 26Calcium ................................ 52 Isoxazolidinones ... . . . ...... . . ....... 41 Southwestern Corn Borer ........... 33Carotenoid Synthesis Inhibitors .... 41 Japanese Beetle ... . . . ...... . . ....... 36 Spider Mite ............................ 37Cell Division Inhibitors ............... 41 Kernel Red Streak ....... . . . . . . . . .... 37 Stewart’s Disease .. . . . . . ............. 24Cereal Leaf Beetle ................... 32 Leaf Freckles and Wilt ............... 26 Stewart’s Wilt .. . . . . . . ................. 24Charcoal Rot .......................... 28 Leaf Miner ................... . . . ....... 36 Stink Bug .............................. 37Chinch Bug .................... . . . . ... 32 Lesser Cornstalk Borer ... . . . . . . .... 36 Sulfonylureas ......................... 40Cladosporium Ear Rot .............. 29 Magnesium ................. . . . ....... 52 Sulfur ................................... 53Common Corn Rust ................. 24 Maize Chlorotic Dwarf Virus .. . . . ... 27 Synthetic Auxins ..................... 41Common Corn Smut ................ 26 Maize Dwarf Mosaic Virus .. . . . . . ... 27 Thrips ................................... 37Common Stalk Borer ................ 32 Manganese ................. . . . ....... 53 Triazines ................................ 42Copper ................................ 52 Mexican Corn Rootworm . . . . ....... 34 Triazolinones .......................... 42Corn Borer ........................... 33 Microtubule Inhibitors ..... . . . ....... 42 Triazolopyrimidines ................... 40Corn Earworm ....................... 33 Molybdenum ........ . . . . . . . . . . ....... 53 Trichoderma Ear Rot ................. 30Corn Leaf Aphid ...... . . . . . . . ....... 31 Nebraska Bacterial Wilt and Triketones .............................. 42Corn Lethal Necrosis .... . . . . . . .... 27 Leaf Freckles ............... . . . ....... 25 True Armyworm ....................... 32Corn Root Aphid .................... 31 Nitriles ........... . . . . . . . . . . . . . . ....... 42 Ureas ................................... 42Corn Rootworm ..................... 34 Nitrogen ........... . . . . . . . . . . . . ....... 53 Webworm ... . . . . . . . ................... 37Corn Stunt Spiroplasma .... . . . . ...27 Northern Corn Leaf Blight ........... 26 Western Bean Cutworm ............. 35Crazy Top .............................27 Northern Corn Rootworm ........... 34 Western Corn Rootworm .. . . . . . . ... 34Cutworm .............................. 35 Northern Leaf Spot ......... . . ....... 25 Wheat Curl Mite ... . . . . . . . ............ 38Cyclohexanediones .......... . . . . .... 40 Penicillium Ear Rot ............ ....... 30 White Grub ............................ 38Dinitroanilines ................. . . ...... 42 Phaeosphaeria Leaf Spot .. . . . ...... 26 Wireworm .............................. 38Diphenyl Ethers .............. . . ...... 42 Phenoxys . . . . . . . . ........... . . . ....... 41 Zinc ..................................... 48Diplodia Ear Rot ............ . . . ....... 30 Phosphinic Acids .......... . . . ....... 41 54
  • Monsanto Company is a member of Excellence Through Stewardship® (ETS). Monsanto productsare commercialized in accordance with ETS Product Launch Stewardship Guidance, and in compliancewith Monsanto’s Policy for Commercialization of Biotechnology-Derived Plant Products in CommodityCrops. This product has been approved for import into key export markets with functioning regulatorysystems. Any crop or material produced from this product can only be exported to, or used, processedor sold in countries where all necessary regulatory approvals have been granted. It is a violation ofnational and international law to move material containing biotech traits across boundaries into nationswhere import is not permitted. Growers should talk to their grain handler or product purchaser to confirmtheir buying position for this product. Excellence Through Stewardship ® is a registered trademark ofBiotechnology Industry Organization.B.t. products may not yet be registered in all states. Check with your Monsanto representative for theregistration status in your state.Individual results may vary, and performance may vary from location to location and from year to year.This result may not be an indicator of results you may obtain as local growing, soil and weather conditionsmay vary. Growers should evaluate data from multiple locations and years whenever possible.ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Roundup Ready® crops containgenes that confer tolerance to glyphosate, the active ingredient in Roundup® brand agricultural herbicides.Roundup® brand agricultural herbicides will kill crops that are not tolerant to glyphosate. Degree ®,Harness ®, TripleFLEX ™ Herbicide, and Warrant ™ Herbicide are not registered in all states. Degree ®,Harness ®, TripleFLEX™ Herbicide, and Warrant™ Herbicide may be subject to use restrictions in somestates. Degree Xtra®, Harness®, and Micro-Tech® are restricted use pesticides and are not registered inall states. The distribution, sale, or use of an unregistered pesticide is a violation of federal and/or statelaw and is strictly prohibited. Check with your local Monsanto dealer or representative for the productregistration status in your state. Tank mixtures: The applicable labeling for each product must be in thepossession of the user at the time of application. Follow applicable use instructions, including applicationrates, precautions and restrictions of each product used in the tank mixture. Monsanto has not testedall tank mix product formulations for compatibility or performance other than specifically listed by brandname. Always predetermine the compatibility of tank mixtures by mixing small proportional quantitiesin advance. Acceleron and Design®, Asgrow and the A Design® , Degree Xtra®, Degree®, Genuity andDesign®, Genuity Icons, Genuity®, Growing Knowledge and Design®, Harness®, Micro-Tech®, RoundupPowerMAX®, Roundup Ready 2 Technology and Design®, Roundup Ready®, Roundup WeatherMAX®,Roundup ®, SmartStax and Design ®, SmartStax®, Technology Development by Monsanto and Design ®,TripleFLEX ™ Herbicide, VT Double PRO™, VT Triple PRO™, Warrant™Herbicide, YieldGard VT and Design®,YieldGard VT Triple®, DEKALB and Design®, Monsanto imagine® and Vine Design®, and When PerformanceCounts ® are trademarks of Monsanto Technology LLC. Permi ® and YUKON ® is a registered trademarkof, and used under license from, Nissan Chemical Industries, Ltd. Ignite®, LibertyLink® and the WaterDroplet Design ®, and Poncho ® are registered trademarks of Bayer. Herculex ® is a registered trademarkof Dow AgroSciences LLC. Authority ® is a trademark of FMC Corporation. Gangster ® and Valor ® areregistered trademarks of Valent U.S.A. Corporation. Respect the Refuge and Corn Design® and Respectthe Refuge® are registered trademarks of National Corn Growers Association. All other trademarks are theproperty of their respective owners. ©2011 Monsanto Company.