Sustainable Management of Soil-borne Plant Diseases


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Sustainable Management of Soil-borne Plant Diseases

  1. 1. SUSTAINABLE MANAGEMENT OF SOIL-BORNE PLANT DISEASES SOIL SYSTEMS GUIDE National Sustainable Agriculture Information Service Abstract: Soil-borne diseases result from a reduction of biodiversity of soil organisms. Restoring beneficial organisms that attack, repel, or otherwise antagonize disease-causing pathogens will render a soil disease-suppressive. Plants growing in disease-suppressive soil resist diseases much better than in soils low in biological diversity. Beneficial organisms can be added directly, or the soil environment can be made more favorable for them through use of compost and other organic amendments. Compost quality determines its effectiveness at suppressing soil-borne plant diseases. Compost quality can be determined through laboratory testing.By Preston SullivanNCAT Agriculture SpecialistIllustrated by Karen McSpaddenJuly 2004© NCAT 2004Why Disease? Plant diseases result when asusceptible host and a disease-causing pathogen meet in afavorable environment. If any Contentsone of these three conditions Why Disease? .............................................1were not met, there would be Strategies for Control:no disease. Many intervention Specific vs. General .....................................3practices (fungicides, methyl General Suppression:bromide fumigants, etc.) focus Disease Suppressive Soils ............................3on taking out the pathogen af- Mycorrhizal Fungiter its effects become apparent. and Disease Suppression .......................4This publication emphasizes Crop Rotation and Disease Suppression ........5making the environment less Plant Nutrients and Disease Control ..............6disease-favorable and the host Compost and Disease Suppression................7plant less susceptible. Why Compost Works .............................9 Determining and Monitoring Plant diseases may occur in Compost Quality .................................11natural environments, but they Direct Inoculationrarely run rampant and cause with Beneficial Organisms .....................12major problems. In contrast, Summary ....................................................12the threat of disease epidemics References..................................................12in crop production is constant. Other Resources..........................................14The reasons for this are becom-ing increasingly evident. Compost Testing Services ......................14 Biocontrol Products ...............................14 Photo by Jeff Vanuga, USDA Natural Resources Conservation Service ATTRA is the national sustainable agriculture information service operated by the National Center for Appropriate Technology, through a grant from the Rural Business-Cooperative Service, U.S. Department of Agriculture. These organizations do not recommend or endorse products, companies, or individuals. NCAT has offices in Fayetteville, Arkansas (P.O. Box 3657, Fayetteville, AR 72702), Butte, Montana, and Davis, California.
  2. 2. Dr. Elaine Ingham, a soil microbiologist and wide diversity of plants grow, their roots com-founder of Soil Foodweb Inc., describes the pro- mingling with a wide diversity of soil organ-gression from undisturbed grassland—where a isms—to a field in row crops. A typical teaspoon of native grassland soil would contain between 600- to 800-million individual bacteria that are members of perhaps 10,000 species. There are several miles of fungi, and perhaps 5000 species of fungi per teaspoon of soil. There are 10,000 individual protozoa split into three main groups, i.e., flagellates, amoebae and ciliates, and perhaps 1000 species of protozoa. There are 20 to 30 beneficial nematodes, which are members of as many as 100 species. Root-feeding nema- todes are quite scarce in truly healthy soils. They are present, but in numbers so low that it is rare to find them. After only one plowing a few species of bacteria and fungi become extinct locally because the food they need is no longer put back in the system. But for the most part, all the sup- pressive organisms, all the nutrient cyclers, all the decomposers, all the soil organisms that rebuild good soil structure are still present and continue to try to do their jobs. Why doesn’t the limited food resources bother them more? A good savings account of organic mat- ter has been built up in native grassland and native forest soil. The soil organisms use the organic matter they “put away” all those years when disturbance did not occur. …But agriculture con- tinues to mine soil organic matter and kill fungi by tilling. The larger predators are crushed, their homes destroyed. The bacteria go through a bloom and blow off huge amounts of that savings account organic-matter. With continued tillage the “policemen” (organisms) that compete with and inhibit disease are lost. The “architects” that build soil aggregates, are lost. So are the engineers, the larger organisms that design and form the larger pores in soil. The predators that keep bacte- ria, fungi and root-feeding organisms in line are lost. Disease suppression declines, soil structure erodes, and water infiltration decreases because mineral crusts form. The decline can take 20 to 30 years to reach the point that most of the natural controls are finally lost and disease runs rampant. The speed with which the “edge” is reached depends on the amount of soil organic matter that was in the soil when it was first plowed, how often the soil was plowed and how much residue was added back. Additionally, how much variety was added back, and the in- oculum base for the disease are also important. Certain diseases don’t occur in some places because the disease hasn’t reached them yet. But the instant the disease does arrive, it goes throughout the fields like a wildfire, because there are few natural competitors to stop it in the soil (1). This progression of decline that Dr. Ingham will suppress disease through competition, an-describes leads to sick soils, and sick soils pro- tagonism, and direct feeding on pathogenic fungi,duce sick crops. As plants and soils have become bacteria, and nematodes. We cannot restore thesicker, growers have responded with newer andmore powerful chemicals in an effort to kill offthe problem pathogens. While it may seem the While it may seem the logical course of action,logical course of action, chemical intervention chemical intervention only serves to make things worse over time.only serves to make things worse over time.Many pesticides reduce the diversity of soil lifeeven further and select for resistant pathogens.This is the history of methyl bromide. Once, thisfumigant was highly effective if used only everyfive years. Today, on the same soils, it must beused much more frequently to keep pathogensunder control. Until we improve the soil life we will continueon this pesticide treadmill. The general principleis to add the beneficial soil organisms and thefood they need—the ultimate goal being thehighest number and diversity of soil organisms.The higher the diversity, the more stable the soilbiological system. These beneficial organisms Photo by Lynn Betts, USDA Natural Resources Conservation ServicePAGE 2 //SUSTAINABLE MANAGEMENT OF SOIL-BORNE PLANT DISEASES
  3. 3. balance of organisms that was present under na-tive, undisturbed circumstances, but we can builda new, stable balance of soil organisms that willbe adapted to the altered soil conditions. This is aproactive plan that moves us toward the desiredoutcome of disease prevention.Strategies for Control:Specific vs. General There are two types of disease suppression:specific and general. Specific suppression re-sults from one organism directly suppressinga known pathogen. These are cases where abiological control agent is introduced into thesoil for the specific purpose of reducing diseaseincidence. General suppression is the result of ahigh biodiversity of microbial populations that Figure 1. Hyphae of the beneficial funguscreates conditions unfavorable for plant diseases Trichoderma wrap around the pathogenic fungusto develop. Rhizoctonia. A good example of specific suppression isprovided by a strategy used to control one of the General Suppression:organisms that cause damping off—Rhizoctoniasolani. Where present under cool temperatures Disease Suppressive Soilsand wet soil conditions, Rhizoctonia kills young A soil is considered suppressive when, in spiteseedlings. The beneficial fungus Trichoderma of favorable conditions for disease to occur, alocates Rhizoctonia through a chemical released pathogen either cannot become established, es-by the pathogen, then attacks it. Beneficial fun- tablishes but produces no disease, or establishesgal strands (hyphae) entangle the pathogen and and produces disease for a short time and thenrelease enzymes that dehydrate Rhizoctonia cells, declines (2).eventually killing them (Figure 1). Currently,Trichoderma cultures are sold as biological seed Suppressiveness is linked to the types andtreatments for damping off disease in several numbers of soil organisms, fertility level, andcrops. For commercial sources of Trichoderma nature of the soil itself (drainage and texture).and other beneficial organisms, see the Other The mechanisms by which disease organismsResources section. are suppressed in these soils include induced resistance, direct parasitism (one organism Introducing a single organism to soils seldom consuming another), nutrient competition, andachieves disease suppression for very long. If direct inhibition through antibiotics secreted bynot already present, the new organism may not beneficial competitive with existing microorganisms. Iffood sources are not abundant enough, the new Additionally, the response of plants growingorganism will not have enough to eat. If soil con- in the soil contributes to suppressiveness. Thisditions are inadequate, the introduced beneficial is known as “induced resistance” and occursorganism will not survive. This practice is not when the rhizosphere (soil around plant roots)sufficient to render the soil “disease suppres- is inoculated with a weakly virulent pathogen.sive”; it is like planting flowers in the desert and After being challenged by the weak pathogen, theexpecting them to survive without water. With plant develops the capacity for future effectiveadequate soil conditions, inoculation with certain response to a more virulent pathogen. In mostbeneficials should only be needed once. cases, adding mature compost to a soil induces //SUSTAINABLE MANAGEMENT OF SOIL-BORNE PLANT DISEASES PAGE 3
  4. 4. disease resistance in many plants. (Using com- suppression. With an abundance of free nutri-post this way will be covered in detail below.) ents, the pathogen can prosper. Virtually any treatment to increase the total microbial activity The level of disease suppressiveness is typi- in the soil will enhance general suppression ofcally related to the level of total microbiological pathogens by increasing competition for nutri-activity in a soil. The larger the active microbial ents. So, how does the plant survive withoutbiomass, the greater the soil’s capacity to use readily available nutrients? It does so throughcarbon, nutrients, and energy, thus lowering microbial associations with mychorrhizal fungitheir availability to pathogens. In other words, and bacteria that live on and near the roots. Thesecompetition for mineral nutrients is high, as most microbes scavenge nutrients for the plant to use.soil nutrients are tied up in microbial bodies. In return the plant provides carbon in the form ofNutrient release is a consequence of grazing by sugars and proteins to the microbes. This symbi-protozoa and other microbial predators: once otic system supports the beneficial organisms andbacteria are digested by the predators, nutrients the plant, but generally excludes the pathogensare released in their waste. that would attack the plant. High competition—coupled with secretion It should be noted that general suppressionof antibiotics by some beneficial organisms and will not control all soil-borne diseases. Rhizocto-direct parasitism by others (Figure 2)—makes nia solani and Sclerotium rolfsii, for example, area tough environment for the pathogen. Our not controlled by suppressive soils—their largegoal is to create soil conditions with all three of propagules make them less reliant on externalthese factors present. Therefore, we want high energy or nutrient sources, and, therefore, theynumbers and diversity of competitors, inhibitors, are not susceptible to microbial competition (3).and predators of disease organisms, as well as With these two pathogens, “specific” beneficialfood sources on which these organisms depend. organisms such as Trichoderma and GliocladiumThe food for beneficial organisms comes either will colonize the harmful propagules and reducedirectly or indirectly from organic matter and the disease potential.waste products from the growth of other organ-isms (1). Mycorrhizal Fungi and Disease Suppression As this discussion of competition suggests, Among the most beneficial root-inhabitinglimiting available nutrients is a key for general organisms, mycorrhizal fungi can cover plant roots, forming what is known as a fungal mat. Figure 2. The nonpathogenic strain of The mycorrhizal fungi protect plant roots from Pythium fungus penetrates the pathogenic diseases in several ways. fungus Phytophthora. • By providing a physical barrier to the invad- ing pathogen. A few examples of physical exclusion have been reported (4). Physical protection is more likely to exclude soil in- sects and nematodes than bacteria or fungi. However, some studies have shown that nematodes can penetrate the fungal mat (5). • By providing antagonistic chemicals. My- corrhizal fungi can produce a variety of antibiotics and other toxins that act against pathogenic organisms. • By competing with the pathogen. • By increasing the nutrient-uptake ability of plant roots. For example, improved phospho- rus uptake in the host plant has commonly been associated with mychorrhizal fungi.PAGE 4 //SUSTAINABLE MANAGEMENT OF SOIL-BORNE PLANT DISEASES
  5. 5. When plants are not deprived of nutrients, Crop Rotation and Disease they are better able to tolerate or resist dis- ease-causing organisms. Suppression• By changing the amount and type of plant Avoiding disease buildup is probably the most root exudates. Pathogens dependent on cer- widely emphasized benefit of crop rotation in tain exudates will be at a disadvantage as the vegetable production. Many diseases build up in exudates change. the soil when the same crop is grown in the same field year after year. Rotation to a non-susceptible In field studies with eggplant, fruit numbers crop can help break this cycle by reducing patho-went from an average of 3.5 per plant to an gen levels. To be effective, rotations must beaverage of 5.8 per plant when inoculated with carefully planned. Since diseases usually attackGigaspora margarita mycorrhizal fungi. Average plants related to each other, it is helpful to groupfruit weight per plant went from 258 grams to 437 vegetable rotations by family—e.g., nightshades,grams. A lower incidence of Verticillium wilt was alliums, cole crops, cucurbits. The susceptiblealso realized in the mycorrhizal plants (6). crop, related plants, and alternate host plants for the disease must be kept out of the field during Protection from the pathogen Fusarium oxys- the rotation period. Since plant pathogens persistporum was shown in a field study using a cool- in the soil for different lengths of time, the lengthseason annual grass and mycorrhizal fungi. In of the rotation will vary with the disease beingthis study the disease was suppressed in mycor- managed. To effectively plan a crop rotation, itrhizae-colonized grass inoculated with the patho- is essential to know what crops are affected bygen. In the absence of disease the benefit to the what disease organisms.plant from the mycorrhizal fungi was negligible.Roots were twice as long where they had grown In most cases, crop rotation effectively con-in the presence of both the pathogen and the trols those pathogens that survive in soil or onmycorrhizal fungi as opposed to growing with crop residue. Crop rotation will not help controlthe pathogen alone. Great care was taken in this diseases that are wind-blown or insect vectoredstudy to assure that naturally-occurring mycor- from outside the area. Nor will it help controlrhizal species were used that normally occur in pathogens that can survive long periods in thethe field with this grass, and that their density on soil without a host—Fusarium, for example.the plant roots was typical (7). Table 1. Rotation periods to reduce vegetable soil-borne diseases (8). Years w/o Vegetable Disease susceptible crop Asparagus Fusarium rot 8 Beans Root rots 3–4 Cabbage Clubroot 7 Cabbage Blackleg 3–4 Cabbage Black rot 2–3 Muskmelon Fusarium wilt 5 Parsnip Root canker 2 Peas Root rots 3–4 Peas Fusarium wilt 5 Pumpkin Black rot 2 Radish Clubroot 7 //SUSTAINABLE MANAGEMENT OF SOIL-BORNE PLANT DISEASES PAGE 5
  6. 6. Rotation, by itself, is only effective on pathogens tion makes plants more tolerant of or resistant tothat can overwinter in the field or be introduced disease. Also, the nutrient status of the soil andon infected seeds or transplants. Of course, dis- the use of particular fertilizers and amendmentsease-free transplants or seed should be used in can have significant impacts on the pathogen’scombination with crop rotation. The period of environment.time between susceptible crops is highly vari- One of the most widely recognized associa-able, depending on the disease. For example, it tions between fertility management and a croptakes seven years without any cruciferous crops disease is the effect of soil pH on potato scab.for clubfoot to dissipate. Three years between Potato scab is more severe in soils with pH lev-parsley is needed to avoid damping off, and three els above 5.2. Below 5.2 the disease is generallyyears without tomatoes to avoid Verticillium wilt suppressed. Sulfur and ammonium sources ofon potatoes. nitrogen acidify the soil, also reducing the inci- A three-year crop rotation is the standard rec- dence and severity of potato scab. Liming, onommendation for control of black rot (Ceratocystis the other hand, increases disease severity. Whilefimbriata), stem rot (Fusarium oxysporum), and lowering the pH is an effective strategy for potatoscurf (Monilochaetes infuscans) in sweet potatoes. scab, increasing soil pH or calcium levels mayRotations may include grasses, corn, and other be beneficial for disease management in manycereals in the Southwest where Texas root rot other crops.(Phymatotrichum omnivorum) is a problem. Adequate levels of calcium can reduce clubroot in crucifer crops (broccoli, cabbage, turnips, etc.).Plant Nutrients and Disease The disease is inhibited in neutral to slightly alkaline soils (pH 6.7 to 7.2) (9). A direct corre-Control lation between adequate calcium levels, and/or higher pH, and decreasing levels of Fusarium Soil pH, calcium level, nitrogen form, and the occurrence has been established for a number ofavailability of nutrients can all play major roles crops, including tomatoes, cotton, melons, andin disease management. Adequate crop nutri- several ornamentals (10). In most cases, crop rotation effectively controls those pathogens that survive in soil or on crop residue.Photo by Tim McCabe, USDA Natural Resources Conservation ServicePAGE 6 //SUSTAINABLE MANAGEMENT OF SOIL-BORNE PLANT DISEASES
  7. 7. the grass absorbed ammonium nitrogen, an acid root zone was created. The pathogen respon- sible for summer patch disease in turf thrives in alkaline soils. This finding supported the usePhoto by Tim McCabe, USDA Natural Resources Conservation Service of ammonium sulfate for grass. Research trials using ammonium sulfate reduced summer patch severity up to 75%, compared to using an equal rate of calcium nitrate (14). A more acid soil also fosters better uptake of manganese. Adequate manganese stimulated disease resistance in some plants. Research at Purdue University showed that uptake of ammonium nitrogen improved plant uptake of manganese and decreased take- all disease (Gaeumannomyces graminis var. tritici) Soil pH, calcium level, (14). Similar results were seen with Verticillium nitrogen form, wilt in potatoes and stalk rot in corn. and the availablility of nutrients can all play major Potassium fertility is also associated with roles in disease management. disease management. Inadequate potash levels can lead to susceptibility to Verticillium wilt in cotton. Mississippi researchers found that cotton Calcium has also been used to control soil- soils with 200 to 300 pounds of potassium per acreborne diseases caused by Pythium, such as grew plants with 22 to 62% leaf infections. Soildamping off. Crops where this has proved ef- test levels above 300 pounds per acre had fromfective include wheat, peanuts, peas, soybeans, zero to 30% infection rate (15). High potassiumpeppers, sugarbeets, beans, tomatoes, onions, levels also retard Fusarium in tomatoes (16). Se-and snapdragons (11). Researchers in Hawaii verity of wilt in cotton was decreased by boostingreported reduction of damping off in cucumbers potassium rates as well (17).after amending the soil with calcium and addingalfalfa meal to increase the microbial populations Phosphate can also be critical. Increasing phos-(11). phorus rates above the level needed to grow the crop can increase the severity of Fusarium wilt Nitrate forms of nitrogen fertilizer may sup- in cotton and muskmelon (10). In general, thepress Fusarium wilt of tomato, while the ammo- combination of lime, nitrate nitrogen, and lownia form increases disease severity. The nitrate phosphorus is effective in reducing the severityform tends to make the root zone less acidic. of Fusarium.Basically, the beneficial effects of high pH are lostby using acidifying ammonium nitrogen. Tomatostudies have shown that use of nitrate nitrogen Compost and Disease Suppressionin soil with an already high pH results in even Compost has been used effectively in the nurs-better wilt control (12). Celery studies showed ery industry, in high-value crops, and in pottingreduced Fusarium disease levels from using cal- soil mixtures for control of root rot diseases.cium nitrate as compared to ammonium nitrate.The nitrate nitrogen form also produced the low- Adding compost to soil may be viewed as oneest levels of Fusarium on chrysanthemums, king of a spectrum of techniques—including coverasters, and carnations (13). cropping, crop rotations, mulching, and manur- ing—that add organic matter to the soil. The It has long been known that the form of ni- major difference between compost-amendedtrogen fertilizer can influence plant disease inci- soil and the other techniques is that organicdence. Research is beginning to reveal why. Dr. matter in compost is already “digested.” OtherJoe Heckman of Rutgers University showed that techniques require the digestion to take placewhen grass roots absorbed nitrate nitrogen, an in the soil, which allows for both anaerobicalkaline root zone condition was created. When and aerobic decomposition of organic matter. //SUSTAINABLE MANAGEMENT OF SOIL-BORNE PLANT DISEASES PAGE 7
  8. 8. Properly composted organic matter is digested search on compost-amended soils for field cropchiefly through aerobic processes. These differ- production. Below is a table that outlines someences have important implications for soil and of the (mostly) field research done on compost-nutrient management, as well as plant health and amended soils and the effects on plant disease.pest management. Chemicals left after anaerobicdecomposition largely reduce compost quality. In some further research, University of FloridaResidual sulfides are a classic example. field trials (21) showed disease suppressive ef- fects of compost and heat-treated sewage sludge Successful disease suppression by compost has on snap beans and southern peas (black-eyedbeen less frequent in soils than in potting mixes. peas). The compost was applied at 36 or 72 tonsThis is probably why there has been much more per acre and the sludge at 0.67 and 1.33 tons perresearch (and commercialization) concerning acre. Bush beans were planted six weeks after thecompost-amended potting mixes and growing organic treatments were applied and tilled in. Af-media for greenhouse plant production than re- ter the bush beans were harvested, a second crop Compost Treatment and Disease Management Pathogen/ Vegetable Treatment Comments Disease Four years of treating Stand thickness and yield Alfalfa “Clover tiredness” fields with high-quality doubled, weeds crowded out compost (no rate given). (18). Disease incidence Drysiphe graminis/ suppressed 95% when 1:1 Barley/Wheat Compost added to soil. Powdery mildew soil:compost mixes used (19). Disease reduced 80% in areas with highest Beans Compost added to soil at compost rates, 40% where (CA blackeye Rhizoctonia sp. varying rates (36-72 tons/ intermediate rates applied. No. 5) acre). Control plots yielded 75 bushels/acre, compost plots yielded 200 bu/acre (20). 1:1 soil:compost mix Young cucumber plants Sphaerotheca sp./ decreased PM by 20% over Cucumber grown in soil/compost mix Powdery mildew control; 1:3 mix decreased of variable rates. infection by 40% (19). Peas seed-treated with Seed treatment; seeds compost extract germinated Pea Pythium sp./ soaked in dilute compost significantly better than (Pisum sativum) Damping off extract, dried before untreated seed in soil sowing. artificially inoculated with Pythium ultimum (19). Compost in combination 40 tons of compost per of hilling plant rows is Peppers Phytophthora sp. acre. best practice to reduce Phytophthora (20). 40 tons of compost per Soybeans Phytophthora sp. Control achieved (20). acre.PAGE 8 //SUSTAINABLE MANAGEMENT OF SOIL-BORNE PLANT DISEASES
  9. 9. of southern peas was planted. A standard fertil-izer program was used. Plant damage from ashystem blight was given a rating of slight, moderate, Salinas, California, strawberryor severe. Rhizoctonia root rot disease ratings grower Tom Jones uses compost onwere made using a scale from 0 to 10, where 10 his 125 acres of berries. Eight of thoserepresented the most severe symptoms. acres have had compost for two years and have just been certified organic. Bean sizes from the compost treatment, at both He uses microbially active, top-qualityapplication rates (36 and 72 T/ac), were larger compost at an eight-ton per acre rate onand yields 25% higher than those from areas re- the organic field and at five-tons per acreceiving no organic amendment. Ashy stem blight on the rest of the fields. Supplementedwas severe in areas with no compost applied. fish emulsion and other liquid fertilizersThe disease was reduced under the sludge treat- are supplied through a drip irrigationment but almost eliminated where compost had system.been applied. Leaf wilting and leaf death werepronounced in that portion of the field where Wisconsin fruit and vegetable farmerscompost was not applied. Richard DeWilde and Linda Halley have grown organic vegetables since 1991. Southern peas as a second crop had greener University scientists are doing researchfoliage and larger plants under both rates of com- on their farm to determine the effect ofpost. Pea yields were significantly higher with compost on health and productivity of36 tons of compost. Where 72 tons of compost vegetable crops and the soil microbialwere used, yields were more than double the community. DeWilde makes qualitynon-amended plots. With the sludge treatment, compost on-farm from dairy and goatyields were comparable or slightly higher than manure, applied at 10 to 15 tons perwhere no amendment was added. Rhizoctonia acre, realizing a 10% yield increase inroot rot caused severe infections, plant stunting, one year. (22)and premature death where no compost wasapplied. Plants growing under the sludge treat-ment suffered severe root infection. Disease wasreduced considerably as compost rates increased teas indeed activate disease resistance genes infrom 36 to 72 tons per acre (21). plants (22). These disease resistance genes are typically “turned on” by the plant in responseWhy Compost Works to the presence of a pathogen. These genes mo- bilize chemical defenses against the pathogen Compost is effective because it fosters a more invasion, although often too late to avoid thediverse soil environment in which a myriad of disease. Plants growing in compost, however,soil organisms exist. Compost acts as a food have these disease-prevention systems alreadysource and shelter for the antagonists that com- running (22). Induced resistance is somewhatpete with plant pathogens, for those organisms pathogen-specific, but it does allow an additionalthat prey on and parasitize pathogens, and for way to manage certain diseases through commonthose beneficials that produce antibiotics. Root farming practices.rots caused by Pythium and Phytophthora aregenerally suppressed by the high numbers and It has become evident that a “one size fits all”diversity of beneficial microbes found in the com- approach to composting used in disease manage-post. Such beneficials prevent the germination ment will not work. Depending on feed stock,of spores and infection of plants growing on the inoculum, and composting process, compostsamended soil (23). To get more reliable results have different characteristics affecting diseasefrom compost, the compost itself needs to be management potential. For example, high carbonstable and of consistent quality. to nitrogen ratio (C:N) tree bark compost gener- ally works well to suppress Fusarium wilts. With Systemic resistance is also induced in plants lower C:N ratio composts, Fusarium wilts mayin response to compost treatments. Hoitink has become more severe as a result of the excess nitro-now established that composts and compost //SUSTAINABLE MANAGEMENT OF SOIL-BORNE PLANT DISEASES PAGE 9
  10. 10. gen, which favors Fusarium (24). Compost fromsewage sludge typically has a low C:N ratio. Some of the beneficial microorganisms thatre-inhabit compost from the outside edges afterheating has subsided include several bacteria(Bacillus species, Flavobacterium balustinum, andvarious Pseudomanas species) and several fungi(Streptomyces, Penicillin, Trichoderma, and Glio-cladium verens). The moisture content followingpeak heating of a compost is critical to the rangeof organisms inhabiting the finished compost.Dry composts with less than 34% moisture arelikely to be colonized by fungi and, therefore,are conducive to Pythium diseases (24). Com-post with at least 40 to 50% moisture will becolonized by both bacteria and fungi and willbe disease suppressive (24). Water is typicallyadded during the composting process to avoida dry condition. Compost pH below 5.0 inhibitsbacterial biocontrol agents (25). Compost madein the open air near trees has a higher diversityof microbes than compost made under a roof orin-vessel (3). Three approaches can be used to increase the Microbiologist Patricia Millner and technician Michaelsuppressiveness of compost. First, curing the Bzdil collect compost samples and gather data on temperature and moisture content.compost for four months or more; second, in-corporating the compost in the field soil severalmonths before planting; and third, inoculating Photo by Stephen Ausmus, USDA Agricultural Research Servicethe compost with specific biocontrol agents (24). For Pythium suppression, there is a direct cor-Two of the more common beneficials used to relation between general microbial activity, theinoculate compost are strains of Trichoderma amount of microbial biomasss, and the degree ofand Flavobacterium, added to suppress Rhizoc- suppression. Pythium is a nutrient-dependenttonia solani. Trichoderma harzianum acts against a pathogen with the ability to colonize fresh plantbroad range of soil-borne fungal crop pathogens, residue, especially in soil that has been fumigatedincluding R. solani, by production of anti-fungal to kill all soil life. The severity of diseases causedexudates. See the Other Resources section for by Pythium and R. solani relates less to the inocu-sources of commercial preparations. lum density than to the amount of saprophytic The key to disease suppression in compost growth the pathogen achieves before infectionis the level of decomposition. As the compost (27). Consequently, soils that are antagonisticmatures, it becomes more suppressive. Readily to saprophytic growth of Pythium—such as soilsavailable carbon compounds found in low-qual- amended with fully decomposed compost—willity, immature compost can support Pythium lower disease levels.and Rhizoctonia. As these compounds are Rhizoctonia is a highly competitive fungus thatreduced during the complete composting pro- colonizes fresh organic matter (28). Its ability tocess, saprophytic growth of these pathogens is colonize decomposed organic matter is decreaseddramatically slowed (26). Beneficials such as or non-existent. There is a direct relationshipTrichoderma hamatum and T. harzianum, unable between a compost’s level of decomposition andto suppress Rhizoctonia in immature composts, its suppression of Rhizoctonia—again pointing toare extremely effective when introduced into the need for high-quality, mature compost. Likemature composts. immature compost, raw manure is conducive toPAGE 10 //SUSTAINABLE MANAGEMENT OF SOIL-BORNE PLANT DISEASES
  11. 11. diseases at first and becomes suppressive after Several companies offer compost quality test-decomposition. In other words, organic amend- ing. Some of these also offer training on howments supporting high biological activity (i.e., to produce disease-suppressive compost. BBCdecomposition) are suppressive of plant-root Laboratories (31) offers a pathogen inhibitiondiseases, while raw organic matter will often assay. This assay can determine the ability offavor colonization by pathogens. your compost sample to directly inhibit specified soil-borne pathogens, including Fusarium, Phy-Determining and Monitoring Compost Quality tophthora, Pythium, and Rhizoctonia. Each assay costs $75 and tests 12 replicates of your compost It is clear that compost’s maturity is a key compared to 12 replicates of a control where thefactor in its ability to suppress disease. The disease organism is uninhibited. They test for achallenge involved in achieving and measuring number of other pathogens in addition to thosethat maturity is the primary reason that compost mentioned above. They can test compost foris not more widely used. Certainly, immature microbial functional groups such as anaerobes,compost can be used in field situations, as long aerobes, yeasts, molds, actinomycetes, pseudo-as it is applied well ahead of planting, allowing manads, and nitrogen-fixing bacteria. Their di-for eventual stabilization. However, good disease versity analysis test looks at how many differentsuppression may not develop due to other fac- kinds of organisms exist within each functionaltors. For example, highly saline compost actually group. This information provides insight intoenhances Pythium and Phytophthora diseases how diverse the microbial populations in yourunless applied months ahead of planting to allow compost are. They also test for compost maturity,for leaching (24). which determines possible toxicity of immature compost to plants. Visit their Web site or call for Dr. Harry Hoitink at Ohio State University more details. (See Other Resources.)has pioneered much of the work associated withdisease suppressive composts. He notes that Midwest Biosystems (32) offers a gradingsuccess or failure of any compost treatment for system for compost quality. Their compostdisease control depends on the nature of the raw grades range from A to D, with A being diseaseproduct from which the compost was prepared, suppressive. From your submitted sample theythe maturity of the compost, and the composting will test for sulfates and sulfides, pathogens, ni-process used. Failure to assess compost quality trogen forms, C:N ratio, seed germination, pH,may be responsible for some of the failures in us- conductivity, redox potential, and sodium anding compost for disease suppression (29). High- moisture levels. This test costs $30 per sample.quality compost should contain disease-sup- An additional test for aerobic plate count andpressive organisms and mycorrhizal innoculum seed germination costs $10. Compost grades are(30). Furthermore, high-quality compost should assigned based on these tests. For a compost tocontain very few if any weed seeds. grade A it must contain 600 to 900 ppm nitrates, no sulfides, meet all lab test guidelines, have a pH from 7.0 to 8.1, and have a 70 to 100% seed germination rate in pure compost. F or more compost information, call and request the ATTRA Soil Foodweb, Inc. (33) offers microbial assays including microorganism diversity and biomass. They will comment on the disease suppressive- publication Farm-Scale ness of a compost sample based on their perfor- Composting Resource List. mance database for highly productive compost and the plant you are planning to put the compost T his resource list is also available on our Web site, on. Call or visit their Web site for prices and sampling instructions. //SUSTAINABLE MANAGEMENT OF SOIL-BORNE PLANT DISEASES PAGE 11
  12. 12. Direct Inoculation with Beneficial Organisms References There are a number of commercial products 1) Ingham, Elaine. 1998. Replacingcontaining beneficial, disease-suppressive or- methyl bromide with compost. Bio-ganisms. These products are applied in vari- Cycle. December. p. 80–82.ous ways—including seed treatments, compostinoculants, soil inoculants, and soil drenches. 2) Schneider, R.W. (ed.). 1982. Sup-Among the beneficial organisms available are pressive Soils and Plant Disease.Trichoderma, Flavobacterium, Streptomycetes, The American Phytopathologi-Gliocladium spp., Bacillus spp., Pseudomonas cal Society. St. Paul, MN. 88 p.spp., and others. A partial list of these productscan be found in the Other Resources section. 3) Granatstein, David. 1998. Suppress-These companies will send you their product ing plant diseases with compost. Goodand technical information upon request. Con- Fruit Grower. May 1. p. 9–11.sider your cost and overall soil health before 4) Ingham, Elaine R. 1991. Interac-trying these products. Dr. Elaine Ingham of the tions among mycorrhizal fungi, rhi-Soil Foodweb offers a perspective on using soil zosphere organisms, and plants. p.inoculants. The essence of her perspective is in 169–197. In: P. Barbosa, V.A. Krischik,the following paragraph. and C.G. Jones (eds.). Microbial Me- Trichoderma and Gliocladium are effective at diation of Plant-Herbivore Interactions.parasitizing other fungi, but they stay alive only as John Wiley and Sons, Inc. 530 p.long as they have other fungi to parasitize. So, these 5) Maronek, D.M. 1981. Mycorrhizal fungifungi do a good job on the pathogenic fungi that arepresent when you inoculate them, but then they run and their importance in horticulturalout of food and go to sleep. In soils with low fungal corp production. p. 172-213. In: Jau-biomass (soils with low organic matter and plenty of rch, R., Horticultural Review. Vol. 3.tillage) these two beneficials have nothing to feed on.Compost is a great source of both the organisms and 6) Matsubara, Yoh-ichi, Haruto Tamura,the food they need to do their jobs. A great diversity and Takashi Harada. 1995. Growthof bacteria, fungi, protozoa and beneficial nematodes enhancement and verticillium wiltexists in good compost (4). control by vesicular-arbuscular mycor- rhizal fungus inoculation in eggplant. Read more of Dr. Ingham’s commentary on Journal of Japanese Horticultural So-the Soil Foodweb Web site, <www.soilfoodweb. ciety. Vol. 64, No. 3. p.>, under the products section. 7) Newsham, K.K., A.H. Fitter, and A.R. Watkinson. 1995. Arbuscular mycor-Summary rhiza protect an annual grass from root pathogenic fungi in the field. Journal Soil-borne diseases result from a reduction of Ecology. Vol. 83. p. 991– the biodiversity of soil organisms. Restor-ing important beneficial organisms that attack, 8) Johnston, S.A., and P.J. Nitzche. Norepel, or otherwise antagonize disease-causing date. Rotation periods suggested tosoil organisms will reduce their populations to help control vegetable diseases. Newa manageable level. Beneficial organisms can Jersey Extension Service. 1 added directly, or the soil environment canbe made more favorable for them with compost 9) Campbell, Robert N., and Arthur S.and other organic amendments. Compost qual- Greathead. 1990. Control of clubrootity determines its effectiveness at suppressing of crucifers by liming. p. 90–101. In:soil-born plant diseases. Compost quality can be A.W. Engelhard (ed.). Managementdetermined through laboratory testing. of Diseases with Macro- and Microele- ments. APS Press. American Phyto- pathological Society, St. Paul, MN.PAGE 12 //SUSTAINABLE MANAGEMENT OF SOIL-BORNE PLANT DISEASES
  13. 13. 10) Jones, J.P., A.W. Engelhard, and S.S. velop suppressiveness to plant pathogens. Woltz. 1989. Management of fu- p. 35-42. In: E.C. Tjamos, G.C. Papavizas, sarium wilt of vegetables and orna- and R.J. Cook (ed.). Biological Control mentals by macro- and microelement of Plant Diseases: Progress and Chal- nutrition. p. 18–32. In: A.W. Engel- lenges for the Future. NATO ASI Series hard (ed.). Soilborne Plant Patho- No. 230. Plenum Press, New York, NY. gens: Management of Diseases with Macro- and Microelements. American 20) Hudson, Berman D. 1994. Soil organic Phytopathological Society. 217 p. matter and available water capacity. Journal of Soil and Water Conserva-11) Ko, Wen-Hsiung, and Ching-Wen Kao. tion. March–April. p. 189-194. 1989. Evidence for the role of calcium in reducing root disease incited by 21) Ozores-Hampton, Monica, H. Bryan, pythium species. p. 205-217. In: Ar- and R. McMillian Jr. 1994. Sup- thur W. Englehard (ed.). Soilborne pressing disease in field crops. Plant Pathogens: Management of Dis- BioCycle. July. p. 60–61. eases with Macro and Microelements. 22) Goldstein, Jerome. 1998. Compost sup- APS Press. St. Paul, MN. 217 p. presses disease in the lab and on the12) Woltz, S.S., and J.P. Jones. 1973. To- fields. BioCycle. November. p. 62–64. mato Fusarium wilt control by ad- 23) Harrison, Una J., and Frank J. Louws. justments in soil fertility. Proceed- 1999. Disease management through sup- ings of the Florida State Horticulture pressive soils. Department of Plant Pa- Society. Vol. 86. p. 157–159. thology, North Carolina State University13) Woltz, S.S., and A.W. Ebgelhard. (draft document). September 23. 14 p. 1973. Fusarium wilt of chrysanthe- 24) Hoitink, H.A.J., A.G. Stone, and mum: effect of nitrogen source and D.Y. Han. 1997. Suppression of lime on disease development. Phy- plant diseases by composts. Hort- topathology. Vol. 63. p. 155–157. Science. Vol. 32, No. 2. p. 184–187.14) Growth Tech Communica- 25) Hoitink, H.A.J., Y. Inbar, and M.J. Boehm. tions. 1996. Disease fighter. Ag. 1991. Status of composted-amended Consultant. March. p. 10. potting mixes naturally suppressive to15) Obrien-Wray, Kelly. 1995. Potas- soilborne diseases of floricultural crops. sium clobbers Verticillium wilt. Soy- Plant Disease. Vol. 75. p. 869–873. bean Digest. January. p. 38. 26) Nelson, E.B., L.L. Burpee, and M.B.16) Foster, R.E., and J.C. Walker. 1947. Lawton. 1994. Biological control of Predisposition of tomato to Fu- turfgrass diseases. p. 409–427. In: A.R. sarium wilt. Journal of Agriculture Leslie (ed.). Handbook of Integrated Pest Research. Vol. 74. p. 165–85. Management for Turf and Ornamen- tals. Lewis Publishers, Ann Arbor, MI.17) Dick, J.B., and H.B. Tisdale. 1938. Fertilizers in relation to incidence 27) Cook, R.J., and K.F. Baker. 1983. The Na- of wilt as affecting a resistant and ture and Practice of Biological Control of susceptible variety. Phytopathol- Plant Pathogens. APS Press, St. Paul, MN. ogy. Vol. 28. p. 666–667 (abstract). 28) Chung, Y.R., H.A.J. Hoitink, and18) Logsdon, Gene. 1995. Using compost for P.E. Lipps. 1988. Interactions be- plant disease control. Farm Scale Com- tween organic-matter decomposition posting. JG Press, Inc. Emmaus, PA. level and soilborne disease sever- ity. Agricultural Ecosystems and En-19) Trankner, Andreas. 1992. Use of agricul- vironment. Vol. 24. p. 183–193. tural and municipal organic wastes to de- //SUSTAINABLE MANAGEMENT OF SOIL-BORNE PLANT DISEASES PAGE 13
  14. 14. 29) Hoitink, Harry, A. 1986. Basis for the <> control of soilborne plant pathogens and click on “product list.” with composts. Annual Review of Phytopathology. Vol. 24. p. 93–114. Companion® Growth Products30) Sances, Frank V., and Elaine R. Ing- P.O. Box 1259 ham. 1997. Conventional organic al- Westmoreland Avenue ternatives to methyl bromide on Cali- White Plains, NY 10602 fornia strawberries. Compost Science 800-648-7626 and Utilization. Spring. p. 23–37. http://www.growthproducts.com31) BBC Labs. See Compost Test- ing Services section below. Liquid drench containing Bacillus subtilis GB03 for horticultural crops at seeding or32) Midwest Bio-Systems. See Compost transplanting or as a spray for turf (EPA ex- Testing Services section below. perimental use permit, see label). Target patho- gen/disease is Rhizoctonia, Pythium, Fusarium33) Soil Foodweb. See Compost Test- and Phytophthora ing Services section below. Kodiak™, Kodiak HB, Kodiak FLOther Resources Gustafson, Inc. 1400 Preston RoadCompost Testing Services Plano, TX 75093 BBC Laboratories, Inc. 800-248-6907 1217 North Stadem Drive 972-985-8877 Tempe, AZ 85281 Dry powder formulation of Bacillus subtilis for 480-967-5931 control of Rhizoctonia solani, Fusarium spp., 480-967-5036 FAX Alternaria spp., and Aspergillus spp. attacking Contact: Vicki Bess roots of cotton and legumes. Can be added to a slurry or mixed with a chemical fungicide for commercial seed treatment. Midwest Bio-Systems Intercept™ 28933—35E Street Soil Technologies Corp. Tampico, IL 61283 2103 185th Street 815-438-7200 Fairfield, IA 52556 815-438-7200 FAX 641-472-3963 800-221-7645 Soil Foodweb, Inc. 1128 NE Second Street Suite 120 A seed inoculant of Pseudomonas cepacia for Corvallis, OR 97330 control of Rhizoctonia solani, Fusarium spp., 541-752-5066 Pythium sp. in corn, vegetables, and cotton. 541-752-5142 FAX NOGALL™ New BioProducts, Inc. 4272 N.W. Pintail PlaceBiocontrol Products Corvallis, OR 97330 The following is a partial list of soil inoculum 541-752-2045and biocontrol products available for control http://www.newbioproducts.comof soil-borne diseases on a variety of plants. Agrobacterium radiobacter strain K-84 forFor a more complete list see the Web site control of crow gall disease caused by Agrobac-PAGE 14 //SUSTAINABLE MANAGEMENT OF SOIL-BORNE PLANT DISEASES
  15. 15. terium tumefaciens in fruit, nut, and orna- mental nursery stock. Used as a dip or spray Bacillus subtilis GB03 plus chemical pesti- for root, stems, or cuttings. cides. Used as a dust seed treatment for Fu- sarium, Rhizoctonia solani, and Pythium in the planter box for seedling pathogens of barley,Mycostop® / Mycostop Mix beans, cotton, peanuts, peas, rice, and soybeans.Ag-Bio Development, Inc.9915 Raleigh St.Westminster, CO 80030 T-22-HC303-469-9221 Bioworks, Inc.877-268-2020 122 North Genesee Street303-469-9598 FAX Geneva, NY 14456 Streptomycetes soil drench for suppression of Trichoderma huzianum Rifai strain KRL- Fusarium, Alternaria, and Phomopsis. Mycos- AG2 for control of Pythium spp., Rhizoctonia top mix used for seed treatment. solani, Fusarium spp., and Sclerotinia homeo- carpa in bean, cabbage, corn, cotton, cucumber,RootShield® peanut, potato, sorghum, soybean, sugarbeet,Bioworks, Inc. tomato, turf, and greenhouse ornamentals. Ap-122 North Genesse Street plied as in-furrow granules, broadcast to turf,Geneva, NY 14456 mixed with greenhouse soil, or mixing powder315-781-1703 with seeds in the planter box or in commercial800-877-9443 seed treatment. Trichoderma fungus for suppression of Py- By Preston Sullivan thium, Rhizoctonia solani, and Fusarium spp. NCAT Agricultural Specialist Applied as granules or wettable powder mixed © NCAT 2004 with soil or potting medium or as a soil drench. Crops include trees, shrubs, transplants, all or- namentals, cabbage, tomatoes, and cucumbers.Soil Guard®Certis-USA, LLC9145 Guilford Road, Suite 175Columbia, MD 21046301-604-7340800-250-5024 Gliocladium virens GL-21 for damping-off and root rot pathogens especially Rhizoctonia solani and Pythium spp. of ornamental and food crop plants grown in greenhouses, nurser- ies, homes, and interior-scapes. Sold as gran- ules.System 3®Helena Chemical Company225 Schilling Blvd.Collierville, TN 38017901-761-0050 //SUSTAINABLE MANAGEMENT OF SOIL-BORNE PLANT DISEASES PAGE 15
  16. 16. The electronic version of Sustainable Management of Soil-borne Plant Diseases is located at: HTML PDF IP 173 Slot 131 Version #071904PAGE 16 //SUSTAINABLE MANAGEMENT OF SOIL-BORNE PLANT DISEASES