South Dakota Walking Your Fields newsletter-July


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Learn more about Goss’s wilt, soybean aphids and the role of water in corn development in this July issue of Walking Your Fields newsletter.

Articles are written by DuPont Pioneer agronomists in South Dakota and distributed on behalf of DuPont Pioneer account managers and Pioneer sales reps.

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South Dakota Walking Your Fields newsletter-July

  1. 1. In South Dakota, annual precipitation varies from 13 to 30 inches per year. This can result in water stress in corn and drought for many areas depending on which end of the spectrum growers find themselves. Water is essential to corn growth, especially at tasseling when the corn‟s uptake of water increases dramatically. From now through the dent stage, corn demands an aver- age of a ¼ inch of water per day. Inability to receive this amount of water can lead to decreased yields. Root growth can help compensate for the increased wa- ter need, as the expansion of the root system reaches deeper into the soil profile to help the plants extract more soil moisture. However, air temperatures also greatly in- fluence water needs. Temperatures in the 90s during corn growth will double the corn water requirement when compared to temperatures in the 60s. Water stress im- pacts corn yield the most during pollination, followed by grainfill and vegetative growth stages. Irrigation is an option to opti- mize yields. Checking your fields using probing methods is important as irrigation must be started early enough to fully benefit the crop and increase yield potential. Most irrigation systems cannot keep up with crop water demands during the later critical growth periods (VT to R3). The first priority for irrigation should be a 3-week period starting just before tassel (VT) and ending just af- ter silking. Corn is less susceptible to water stress during later grain-development stages (R3). Soil water levels should be maintained to allow the crop to reach maturity (R6). Understanding Water Usage in Corn Water is acquired, used and lost through evapotranspira- tion (ET). In this process, water is removed directly from the soil surface to the atmosphere by evaporation and through the plant by transpiration. Plant transpiration is the evaporation of water from leaf and other plant surfac- es. For corn, evaporation often accounts for 20 to 30 per- cent and transpiration 70 to 80 percent of total ET over the length of a growing season. The amount of water retained for the plant is affected by the soil texture and organic matter. Soil serves as a res- ervoir to the plant, even though not all water is accessible to the plant. Water held by the soil between field capacity and permanent wilting point is called “plant-available wa- ter” and varies by soil texture. Ranges of available water at fine sandy soil are 0.7 to 1 inch, increasing up to clay which holds 1.8 to 2.4 inches. As soil dries, water stress can occur at 50 percent or less of plant-available water. In many cases, irrigation is in- stalled to compensate for decreased precipitation. Using irrigation can increase yield up to 30 percent by decreas- ing ET. WALKING YOUR FIELDS® newsletter is brought to you by your local account manager for DuPont Pioneer. It is sent to customers throughout the growing season, courtesy of your Pioneer sales professional. The DuPont Oval Logo is a registered trademark of DuPont. PIONEER® brand products are provided subject to the terms and conditions of purchase which are part of the labeling and purchase documents. ®, TM, SM Trademarks and service marks of Pioneer. © 2013 PHII. Role of Water in Corn Development Table 1. Estimated Corn Evapotranspiration and Yield Loss per Stress Day During Various Growth Stages Growth Stage Evapo- transpiration* (inches/day) % yield loss per day of stress (min-ave-max) Seedling to 4 leaf 0.06 --- 4 leaf to 8 leaf 0.10 --- 8 leaf to 12 leaf 0.18 --- 12 leaf to 16 leaf 0.21 2.1 - 3.0 - 3.7 16 leaf to tasseling 0.33 2.5 - 3.2 - 4.0 Pollination (R1) 0.33 3.0 - 6.8 - 8.0 Blister (R2) 0.33 3.0 - 4.2 - 6.0 Milk (R3) 0.26 3.0 - 4.2 - 5.8 Dough (R4) 0.26 3.0 - 4.0 - 5.0 Dent (R5) 0.26 2.5 - 3.0 - 4.0 Maturity (R6) 0.23 0.0 Adapted from Rhoads and Bennett (1990) and Shaw (1988). From: What Happens Within The Corn Plant When Drought Occurs? Joe Lauer, Uni- versity of Wisconsin-Extension, 2003. *Evapotranspiration is the total of the water used by the corn plant and water lost to evaporation. Photo: DuPont Pioneer WALKING YOUR FIELDS ® July 24, 2013 - Issue 4
  2. 2. Goss‟s wilt is beginning to show up in corn fields around the central U.S. again this year. In 2012, the disease was found throughout much of the area despite the dry condi- tions in late summer and fall. This season, high winds along with sand/soil blasting that has occurred throughout June have likely created the kinds of injury necessary for Goss‟s wilt bacteria to enter corn plants. The prolonged wet weather this spring is conducive to bacterial diseases in many crops, and corn has been no exception. Goss‟s wilt is caused by a bacte- rial pathogen and doesn‟t respond to treatment with fun- gicides. It is best managed with resistant hybrids and sound cultural practices. Typical signs and symptoms of Goss’s wilt  Long, water-soaked, grayish-green patches or streaks that turn to large dead streaks with wavy margins  Dark „freckles‟ appear within or just outside of leaf le- sions  Lesions appear to spread along leaf veins (characteristic of bacterial disease)  Yellow-orange bacterial ooze (or dried ooze appearing as shiny flecks)  Stems may become plugged with bacteria, vascular bundles appearing orange to brown The disease generally starts from inoculum surviving on previous (corn) crop residues, found at or near the soil surface. Early-season rainfall, especially when heavy or associated with high winds can lead to infection of the young corn crop. Early infection can produce the most devastating symptoms, including wilting and early plant death. Later infections typically affect leaves primarily, but may lead to early maturity, or reduced ear size and lower yields depending on the area affected and time of symptom onset. Risk factors to consider when planning for Goss’s wilt management:  History of the disease in a field in last year or two indi- cates presence of inoculum  Continuous corn raises the risk of inoculum build-up  Reduced tillage tends to lead to slower residue break- down and greater risk that inoculum will remain in af- fected fields  Irrigated fields tend to have higher levels of disease incidence and severity As in-season manage- ment of Goss‟s wilt is difficult or impossible, be sure to select hy- brids with the highest resistance level availa- ble for areas that have multiple risk factors mentioned above. Goss’s Bacterial Wilt & Blight Positive Goss‟s Wilt sampling sites in ND, SD, MN and WI in 2012. Goss‟s wilt symptoms on corn leaf. Photo: DuPont Pioneer Dried bacterial ooze (black arrows) and freckles (white arrows) are diagnostic of Goss‟s Wilt. Photo: DuPont Pioneer A stem cross-section showing vascu- lar bundles discolored orange to brown. Photo:T.Jackson,Univ.ofNebraska
  3. 3. Soybean aphids are right on schedule. Even if you planted soybean seeds treated with a nicotinoid insecticide to delay aphid population establish- ment, you will still want to scout your fields for this pest from V5 through R5. The soybean aphid overwin- ters in buckthorn and migrates to legumes (soybeans, alfalfa and clovers) in July. It‟s less than 1 mm in length but when left untreated, economic infestations can reduce yields by more than 10 bushels/ acre. Symptoms Aphid-infested soybean plants may look simi- lar to a potassium deficiency: curled leaves, often yellow on the outside. Aphids produce a sugary excrement, known as honeydew, on leaves, which promotes soot mold growth and can serve as a feeding ground for ants. Plants infested by the soy- bean aphid will also appear shorter. Besides a stunted plant with noticeable discoloration, you can also detect these oval- shaped, light green pests with black “tail pipes” near the end of the abdomen by doing numerous sweeps through the field. Take Action Count the number of aphids on 30 to 50 plants throughout the entire field and calculate the aver- age number of aphids per plant. If aphid populations reach 250 per plant and are increasing during the R1 – R5 growth stages, consider a foliar insecticide to con- trol the population. Your local Pioneer sales rep can help with product recom- mendations. There are also several beneficial in- sects that feed on soybean aphids and can naturally control the aphid popula- tion. They include Asian lady beetles, damsel bugs, green lacewing larvae, and insidious flower bugs. Pioneer® Field360™ Select software is an interactive, web-based subscription service that combines your field data with real- time agronomic and weather information  Track field by field Precipitation and GDUs using Field 360 Select  Scouting 101 with GPS located as-planted Products  On-The-Go organized field applied data Pioneer Field360 Notes pinpoints your field location via satellite imagery so you can record notes or photos on the spot.  Displays field boundaries for DuPont Pioneer custom- ers  Easy to use interface; available for iOS and Android Systems  Instantly map and organize data with notes and photos  Share your data from the field via email Contact your local Pioneer professional for more Info! Pioneer has seen continued growth in sales in the Dako- tas in recent years. In response to this growth. many tal- ented people have been hired to be part of this expanding geography. Also, many employees have taken on new roles and responsibilities in different areas. Troy Boomsma is the new Account manager in the Yank- ton Area. He replaces Myles Konopasek who has been promoted to Area Manager. Greg Kleinhans is the new Account Manager south of Sioux Falls, replacing Kyle Kayser. Kyle has taken on a new role as Field Agrono- mist for Southern SD. Kyle Christensen is the Product Agronomist for the same geography. Jim Ruhland was named Field Agronomist a few months earlier. Taking over for him in the Mitchell area is Pat VanLith. Jon Fer- ris is the new Account Manager in the area south of Hu- ron and west of Brookings. These changes are reflected on the back page of this issue. We appreciate your continued support and business! And as always, we are here to help you succeed. The Continued Growth of DuPont Pioneer Soybean Aphids Aphids found on soybean leaves. Photo: Josh Shofner and Brian Buck 7/5/13 Soybean aphids and an ant on a soybean leaf. Aphids excrete “honeydew,” a sugary substance that attracts other insects and also results in development of sooty mold. Photo: Marty Lovrien Photo: Bruce Carlson Soybean aphid damage on soybean leaves.