White Mold of Soybean Web Book
CPN 1026. Published February 10, 2022. DOI: doi.org/10.31274/cpn-20210607-0
Damon Smith, University of Wisconsin; Adam Sisson, Iowa State University; Martin Chilvers, Michigan State University; Mehdi Kabbage, University of Wisconsin-Madison; Megan McCaghey, University of California-Davis; and Jaime Willbur, Michigan State University.
Characteristic white mold symptoms and signs.
White mold often ranks among the top yield-reducing soybean diseases in the northern United States and Canada. Researchers estimate that white mold caused more than 101 million bushels of soybean yield loss in the U.S. and Ontario, Canada from 2010 to 2014 (Allen et al., 2017). Losses were much higher from 2015 to 2019, when yield reduction caused by white mold was estimated to have exceeded 201 million bushels (Bradley et al., 2021). This is likely a result of more susceptible genetics being deployed, aggressive management to increase yield, and changing climatic conditions.
Developing a white mold management plan based on field history and best management practices (BMPs) can reduce yield losses caused by white mold. Integrating several management practices including cultural control, varietal resistance, scouting, prediction tools, and chemical and biological control can form an effective management plan for white mold.
For current white mold updates:
Wisconsin Crop Manager from the University of Wisconsin-Madison
Integrated Crop Management News from Iowa State University
Field Crops from Michigan State University
Pest and Crop Newsletter from Purdue University
Farmdoc from University of Illinois
White mold forecasting and management apps:
Sporecaster, a white mold forecasting tool for iOS and Android.
Sporebuster, a white mold fungicide decision tool for iOS and Android.
Earn 0.5 Certified Crop Advisor CEUs after reading this web book. Click here for the quiz.
Use the Table of Contents on this page to navigate between chapters and resources available as part of this text.
© 2022 Crop Protection Network unless otherwise noted. All rights reserved.
Disease distribution
White mold of soybean in North America was discovered in 1946 in Ontario, Canada and the United States in 1948 (Central Illinois) and became a chronic problem in Michigan, Minnesota, and Wisconsin by the 1970s. The remainder of the North Central states experienced no problems with the disease during this time. Even in the Great Lakes states, white mold outbreaks were generally localized, occurring when soybeans were rotated with susceptible crops such as dry edible beans but was not considered a threat to soybean production.
Occurrence of white mold started to become widespread in each of the Great Lakes states and Ontario in 1990 and was prevalent throughout the other North Central states and Quebec by 1992. The expanded geographic range and more frequent occurrence of white mold changed it from a sporadic disease to a yearly threat throughout the upper North Central soybean production region (Figure 1). The reasons for this sudden increase of white mold in the region are not entirely understood.
Although not fully documented, there is evidence suggesting the genetic base of current soybean varieties has changed, resulting in greater susceptibility to the white mold pathogen compared to older varieties. The push for increased yield has also led to narrow row spacing and high plant populations, which are also conducive for the development of white mold. Shifts in corn herbicide usage and rates (i.e., triazine herbicides) have been presented as another reason for increased white mold. Changing climate may also be contributing to the expansion in the range of the disease. Warmer summers often result in increased moisture, which can lead to prolonged favorable conditions for the white mold fungus.
Figure 1. White mold distribution in the United States and Canada.
Mimi Broeske
Yield loss and seed quality
White mold causes yield loss in soybean by reducing seed number, weight, and marketability of the grain. Sclerotia may contaminate harvested grain, which may cause price reductions for the presence of foreign material delivered at the elevator (Figure 2). S. sclerotiorum can also infect soybean seed (Figure 3) and be an important source of inoculum if planted into fields with no history of white mold. Infected seed can have reduced germination, and in some cases, oil and protein content can also be reduced.
Figure 2. Sclerotia of S. sclerotiorum in harvested soybeans.
Daren Mueller
Figure 3. Soybean pod infected by S. sclerotiorum.
Daren Mueller
Yield and economic losses from white mold occur every year. Disease development, and thus losses, are greatly impacted by yearly environmental conditions. For example, 2012 and 2020 were relatively dry years, and because moisture is necessary for white mold development, these years had fewer yield losses due to white mold than other years (Table 1).
Table 1. Estimated annual losses attributed to white mold of soybean from 2010 to 2020 from participating states across the United States and Ontario, Canada. This data is from the Crop Protection Network Field Crop Disease and Insect Loss Calculator.
Year | Bushels Lost (in thousands) | $ Loss (USD in thousands) | $ Loss per Acre (USD) |
2010 | 24,520 | $274,635 | $3.45 |
2011 | 12,775 | $156,869 | $2.03 |
2012 | 5,530 | $78,768 | $0.99 |
2013 | 17,666 | $229,057 | $2.90 |
2014 | 40,855 | $413,892 | $4.82 |
2015 | 42,723 | $368,587 | $4.33 |
2016 | 39,682 | $372,791 | $4.35 |
2017 | 60,928 | $558,845 | $6.00 |
2018 | 24,172 | $208,579 | $2.27 |
2019 | 31,076 | $266,543 | $3.37 |
2020 | 8,280 | $91,395 | $1.06 |
Further information on white mold loss data can be queried by state, region, and additional years using the Field Crop Disease and Insect Loss Calculator from the Crop Protection Network.
Yield can be reduced by 5 bushels for every 10 percent increase in white mold incidence. Researchers studying white mold typically record disease incidence and severity data using a rating scale and combine these into a disease severity index score (DIX). By combining DIX scores with yield loss analyses, control thresholds for cost-effective management can be identified.
Recent research revealed little yield loss (0.4-0.9 bushels per acre) occurred at 25-30 percent DIX when the crop growth stage was between R6 and R7 (maturity). When DIX was greater than 40 percent, yield decreased more dramatically – yield loss was considerable starting at approximately 65 percent DIX. For every 10 percent increase in DIX after 65 percent, there was a corresponding soybean yield loss of approximately 10 bushels per acre.
Sclerotinia sclerotiorum, the fungus that causes white mold, produces apothecia, which are mushroom-shaped fungal structures, prior to disease appearance in the field. Apothecia grow from hard, black structures in the soil called sclerotia that resemble mouse droppings (Figure 1). Field scouts may confuse harmless fungi such as the common bird’s nest fungus with apothecia. (Gallery 1).
Figure 1. Sclerotia in soil prior to germination of apothecia.
Roger Schmidt
Apothecia growing from sclerotia. Image: Roger Schmidt
White mold apothecia growing from sclerotia on soil surface. Image: Craig Grau
Fungi that may be confused with white mold apothecia. Image: Brandon Kleinke
Fungi that may be confused with white mold apothecia. Image: Brandon Kleinke
Fungi that may be confused with white mold apothecia. Image: Brandon Kleinke
Fungi that may be confused with white mold apothecia. Image: Brandon Kleinke
Gallery 1. Apothecia and commonly confused fungi.
Plant disease symptoms are caused by physiological changes in the plant as a reaction to the pathogen. Symptoms of white mold can include water-soaked stem lesions that rapidly progress above and below infected nodes and eventually encircle the stem (Figure 2). Over time, infected stems become bleached and stringy (Figure 3). Lesions can also occur on stems, pods, petioles, and, rarely, on leaves. See Gallery 2 for more images of white mold symptoms.
Figure 2. Early development of white mold on soybean stem.
Daren Mueller
Figure 3. Soybean stem bleaching.
Adam Sisson
Severe infection weakens the plant and can result in wilting, lodging, and plant death. White mold often occurs in patches in the field (Figure 4).
Signs are visible parts of the fungus that causes disease and can assist in diagnosis. The signs of the white mold fungus include white cottony mycelia (moldy growth) and sclerotia on infected plant tissues. Sclerotia may be produced inside or outside of stems and pods. Signs of S. sclerotiorum can help distinguish white mold from most other soybean diseases (Gallery 2).
Figure 4. Patch of white mold in a soybean field.
Daren Mueller
Early white mold stem lesion. Image: Daren Mueller
Foliar symptoms caused by white mold. Image: Daren Mueller
White mold infected plants with wilted, dead leaves still attached. Image: Adam Sisson
Mycelium and sclerotia on soybean stem. Image: Daren Mueller
Sclerotia inside soybean stem. Image: Daren Mueller
White mold infected soybean. Image: Daren Mueller
Bleached soybean pod with mycelium. Image: Daren Mueller
Soybean pod interior showing white mold mycelium. Image: Daren Mueller
Soybean pod with mycelium and sclerotia. Image: Daren Mueller
Gallery 2. White mold symptoms and signs in soybean.
Sclerotinia sclerotiorum survives in the soil as sclerotia. When soils are shaded, moist, and cool, sclerotia within the top two inches of the soil profile can germinate to produce apothecia. Development of apothecia is favored when the 30-day average, maximum ambient air temperatures are below 68ºF (20ºC). In order to offset the cooling that occurs in irrigated fields, a higher 30-day average, maximum air temperature > 80ºF (27ºC) may be required for apothecial development. Apothecia are small (approximately 1⁄8- to 1⁄4-inch (3-6 mm) in diameter), tan, cup-shaped mushrooms. Apothecia produce millions of spores called ascospores that typically infect soybean plants via senescing flowers (see video below). In soybean, ascospore dispersal is short-distance, with most ascospores being deposited within a few meters of the source of inoculum (Wegulo et al., 1999). Infection by ascospores is favored by maximum daily temperatures lower than 85ºF (32ºC) and frequent moisture from rain, fog, dew, or high relative humidity. A dense and nearly closed soybean canopy during flowering (growth stages R1 through R3) provides a favorable microenvironment for white mold development.
For white mold to develop, there must be a presence of the white mold fungus in a field, an environment favorable for apothecial development, ascospore infection and disease development, and a susceptible soybean variety, all occurring at the same time (Figure 1). Early canopy closure creates conditions favorable for disease. Factors that promote early canopy closure and favor white mold in soybean include narrow row spacing, high plant populations, a high yield potential crop with a dense canopy, and planting a susceptible variety. A field history of white mold and susceptible crops (mostly broadleaf crops) in the rotation greatly increases risk potential as most pathogen inoculum originates from within the soybean field.
Figure 1. The three factors required for soybean white mold to occur include presence of the white mold pathogen, a susceptible soybean host, and an environment conducive to disease. This concept is called the disease triangle. When any of these three things are missing, white mold will not develop.
Iowa State University Integrated Pest Management Program
Disease cycle
It is important to understand the disease cycle of white mold to better manage this disease. Referring to Figure 2, the disease cycle begins with survival of sclerotia of S. sclerotiorum in the soil (A). Sclerotia germinate, producing apothecia (B). Ascospores are produced in apothecia (C). Senescing soybean flowers are colonized by ascospores. Infection spreads from the nodes into the stem (D). Signs of S. sclerotiorum include sclerotia and fluffy, white mycelium. Symptoms include bleached stem lesions, wilt, lodging, and plant death resulting in poor pod fill or no seeds (E). Sclerotia form on exterior and interior of stems and pods and drop to the soil during soybean harvest (F).
Figure 2. White mold disease cycle.
Iowa State University Integrated Pest Management Program
White mold is especially problematic in fields with dense canopies during early reproductive growth stages, coupled with rain, fog, or dew. These conditions create a shaded, cool, moist microclimate conducive to disease development.
Seasonal and long-term factors favoring white mold risk in soybean include a high yield potential crop with a dense canopy, planting a susceptible variety in a field with a history of white mold, and a history of susceptible crops in the rotation. Factors favoring a dense canopy and white mold risk include early planting, narrow row width, high plant populations, and high soil fertility.
Scout near tree lines or other parts of a field that experience less wind disturbance; parts of the field with thick canopies; and fields with a history of white mold. White mold often occurs in patches within fields. Within these patches, look for scattered dead plants. For information on good field scouting practices, see the Crop Scouting Basics for Corn and Soybean web book or the Virtual Crop Scout School webinars from the Crop Protection Network.
Yield loss is more severe when plants die prematurely, or when stems are girdled. In addition to causing yield loss, white mold can impact seed quality, and if sclerotia are present in the seed lot, reduce the grain sale price because of foreign material at the elevator. After harvest, check seed lots for sclerotia and infected seeds. Infected seeds are usually smaller, lighter, white, and chalky.
Taking accurate notes about where and how much white mold occurs in each soybean field is important for future disease management planning. Tracking disease levels across years will also help determine the potential sclerotia (inoculum) load and the disease risk that may be present in a particular field in the future. Research has demonstrated that for every 10% increase in disease incidence recorded from white mold, nearly 1 kg/ha (0.89 lb/a) of sclerotia can be returned to the soil per acre at harvest. This translates to thousands of sclerotia per acre being returned to the soil and available for future epidemics if the pathogen is left unchecked.
White Mold Forecasting
A smartphone app has been developed to help farmers and crop managers to make the decision to apply fungicides at the optimum time. The app is called Sporecaster and uses GPS-referenced weather data and information the user provides about crop growth stage and row-spacing. Sporecaster then uses statistical models and weather inputs for the field location to provide an estimation of risk of infection during the bloom period. These estimates of probability help users make a decision to spray or not to spray.
Sporecaster is available for iOS and Android.
How to use the Sporecaster app for white mold disease forecasting
Scouting for White Mold
Diseases confused with white mold
Symptoms and signs of white mold can be confused with those caused by several other soybean diseases (Gallery 1). However, white mycelium on the soybean stem and dark sclerotia are distinguishing signs of white mold infection.
Downy mildew on soybean seed. Image: X.B. Yang
Phomopsis seed decay. Image: Daren Mueller
Brown stem rot foliar and stem symptoms. Image: Adam Sisson
Charcoal rot on soybean stems. Image: Adam Sisson
Phytopthora root and stem rot characteristic stem lesion. Image: Daren Mueller
Southern blight mycelial growth on soybean stems. Image: Tom Allenn
Stem canker symptoms on soybean stems. Image: Adam Sisson
Soybean sudden death syndrome foliar symptoms. Image: Daren Mueller
Gallery 1: Diseases that may be confused with white mold.
Multiple management tools are available, and incorporation of multiple strategies is the best way to manage white mold. Additionally, management is informed by taking accurate field notes and using the available prediction tools.
Recordkeeping
Taking accurate notes about where and how much white mold occurs in each soybean field is important for future disease management planning. Sclerotia can survive up to eight years in soil. Tracking disease levels across years also will help to determine the potential sclerotia inoculum load that may be present in a particular field. Recording disease and yield performance for different varieties will help in variety selection for fields with a history of white mold. Farmers with precision planting capabilities may also find it useful to map specific locations within fields where white mold occurs. This enables targeted fungicide applications and planting population adjustments for these specific areas.
Cultural Control
Crop Rotation
A minimum of two to three years of a non-host crop, such as corn, flax, or small grains (for example, wheat, barley, or oat), can reduce the number of sclerotia in the soil. Forage legumes, such as alfalfa and clovers, are less susceptible to infection but are hosts for S. sclerotiorum. Soybean fields that have a history of white mold should not be in two- or three-year rotations with broadleaf hosts such as edible beans, canola, cole crops (cabbage, broccoli, etc.), pulse crops (peas, chickpeas, and lentils), sunflowers, and potatoes.
Tillage
The impact of tillage on white mold development has proven inconsistent. Deep tillage may initially reduce white mold incidence by removing sclerotia from the upper soil profile. However, sclerotia can remain viable for more than three years if buried 8-10 inches (20-25 cm) in the soil and may be returned to the soil surface in subsequent tillage operations. Sclerotia may degrade faster in no-till production systems since more sclerotia are found near the soil surface therefore avoid planting another susceptible crop the following year.
Plant Populations
High plant populations contribute to dense, closed canopies. Greater plant populations have been associated with increased incidence of white mold. Consider decreasing plant populations while still maintaining populations required for good yield in your area. Use the lowest possible seeding rate that will achieve the recommended final plant density for your area. Local extension agronomists can help determine this number.
Row Spacing
Soybean planted into narrow rows may lead to faster and more complete canopy closure around the time of soybean flowering (Figure 1). Moving from 15-inch to 30-inch row spacing can sometimes reduce white mold severity by as much as 50 percent. However, moving to a wider row spacing can, in some cases, result in lower yield potential compared to narrow row spacings.
Figure 1. Narrow row spacings can promote white mold development.
Adam Sisson
Planting Date and Relative Maturity
Early planting, late-maturing varieties, and varieties with a bushy architecture or that have a tendency to lodge can contribute to more closed canopies. However, direct impact of these factors on white mold incidence and yield varies, because disease development is highly dependent on weather conditions during the reproductive growth stages.
Fertility and Plant Nutrition
High soil fertility, especially the use of nitrogen-rich manures and fertilizers, favors white mold development by promoting lush plant growth and early canopy closure. The application of manure should be avoided on fields with a history of white mold.
Weed Control
Many common broadleaf weeds found in fields used for soybean production also are hosts of S. sclerotiorum (Table 1). High weed populations may also contribute to the plant canopy density, favoring disease development.
Table 1. Common host weeds of S. sclerotiorum. Adapted from Peltier et al. 2012.
Canada thistle | Common vetch | Redroot pigweed |
Catchweed bedstraw | Curly dock | Shepard's purse |
Common burdock | Dandelion | Sow thistle |
Common chickweed | Field pennycress | Toothed spurge |
Common cocklebur | Henbit | Velvetleaf |
Common lambsquarters | Hemp | Venice mallow |
Common purslane | Jerusalem artichoke | Wild carrot |
Common ragweed | Jimsonweed | Wild mustard |
Common sunflower | Prickly lettuce | Wild parsnip |
Cover Crops
The use of small grain cover crops (like oat, wheat, or barley) grown with soybean can stimulate earlier emergence of apothecia compared to soybean grown alone. This can potentially lower white mold incidence. Consider first how cover crops may affect soil moisture, availability of soil nutrients, and shading before implementing. In organic systems, planting into roller-crimped rye cover crops can substantially reduce white mold incidence and severity. The mat of rye left after roller-crimping produces a dark environment at the soil surface that is not conducive for complete apothecial development. The thick rye mat may also function as a physical barrier limiting ascospore release and movement.
Irrigation Management
Avoid excessive and frequent irrigation during flowering. Low moisture levels within the soybean canopy are critical for reducing the potential for white mold development. Infrequent, heavy watering is better than frequent, light watering.
Variety Selection
Moderately resistant soybean varieties are available (Figure 2). Although resistant varieties contribute to lower disease severity, some disease development will occur when conditions favor white mold. Plant the least susceptible variety in fields with a history of white mold. Severity of white mold also depends on soybean genetics. Specific genetic traits can help plants avoid infection, or traits can contribute to physiological resistance where plants actively battle infections. The Crop Protection Network (CPN) publication Improved Screening method for Genetic Resistance to White Mold (Sclerotinia stem rot) in Soybean (CPN-5006) outlines a procedure that enables quicker identification of resistant soybean plants and allows for comparisons across different soybean breeding programs.
Figure 2. White mold on velvetleaf, a common broadleaf weed found in soybean fields.
Daren Mueller
Figure 3. White mold-resistant soybean variety (upper middle) planted among disease-susceptible plants.
Craig Grau
Chemical Control
Fungicides (and some PPO herbicides such as lactofen) can be a part of an integrated management system for white mold. Some foliar-applied fungicides and herbicides have efficacy against white mold, although none offer complete control.
Fungicides inhibit infection and growth of S. sclerotiorum, but how inhibition occurs depends on product selection. There are numerous products on the market that are labeled for white mold management. Table 2 includes products and programs that are most commonly used and have been evaluated in diverse locations. All of the effective products have limited upward movement in plant tissues, and none move downward in the plant where infection often occurs.
Herbicides containing lactofen as the active ingredient (Cobra® or PhoenixTM) do not directly inhibit S. sclerotiorum, but may reduce white mold incidence.
Lactofen can modify the soybean canopy and delay or reduce flowering, which may alter the availability of potential infection sites for S. sclerotiorum.
Lactofen also can induce a systemic acquired resistance (SAR) response that increases production of antimicrobial chemicals known as phytoalexins (for example, glyceollin) by the soybean plant. Phytoalexins can inhibit the growth of S. sclerotiorum. Although these herbicides have potential benefits, their use may result in crop damage that can reduce yields, particularly in years not conducive for disease.
The Crop Protection Network (CPN) publication Pesticide Impact on White Mold (Sclerotinia Stem Rot) and Soybean Yield (CPN-5001) details the efficacy and economics of using the pesticide programs listed in Table 2. It should be noted that some of the more efficacious programs are often more expensive. Thus, the economics of using a particular program should be considered relative to your soybean yield potential and grain sale price.
Table 2. The common active ingredients and associated treatment costs evaluated in white mold pesticide efficacy trials. Adapted from Willbur et al. 2019.
Active lngredient(s) | Trade Name (suggested application stage) | Typical Application Rates | Active Ingredient Cost ($/A) | Application Cost ($/A) | Total Treatment Cost ($/A)¹ |
boscalid | Endura® (R1) | 8.0 oz. | $38.76 | $7.28 | $46.05 |
boscalid + fluxapyroxad + pyraclostrobin | Endura® (R1) fb² Priaxor® (R3) | 6.0 oz. fb 4.0 fl. oz. | $46.94 | $14.57 | $61.51 |
fluazinam | Omega® (R1) | 12.0 fl. oz. | $36.85 | $7.28 | $44.14 |
fluoxastrobin + flutriafol | Fortix® (R1) | 5.0 fl. oz. | $16.33 | $7.28 | $23.61 |
lactofen | Cobra® (R1) | 6.0 fl oz. | $9.04 | $7.28 | $16.33 |
picoxystrobin | Aproach® (R1) fb Aproach® (R3) | 9.0 fl. oz. fb 9.0 fl. oz. | $39.94 | $14.57 | $54.51 |
prothioconazole | Proline® (R1) fb Proline® (R3) | 5.0 fl. oz. fb 5.0 fl. oz. | $46.18 | $14.57 | $60.75 |
prothioconazole + trifloxystrobin | Proline® (R1) fb Stratego YLD® (R3) | 3.0 fl. oz. fb 4.0 fl. oz. | $28.64 | $14.57 | $43.21 |
tetraconazole | Domark® (R1) | 5.0 fl. oz. | $13.32 | $7.28 | $20.60 |
thiophanate-methyl | Topsin® (R1) | 20 fl. oz. | $7.26 | $7.28 | $14.54 |
non-treated control | _ | _ | $0.00 | $0.00 | $0.00 |
¹Total Treatment Cost is the sum of the chemical list price and application cost; ²fb = followed by. Several programs involve two fungicide applications. Those are indicated by fb in the trade name column.
Sporebuster
Recent university research was used to develop Sporebuster, a smartphone application for iPhone and Android platforms. The app was funded by soybean checkoff dollars and is freely available. Sporebuster helps farmers make economic decisions when they are selecting pesticides and deciding when to apply them to manage white mold. Sporebuster can run various scenarios – when disease pressure is low, medium, or high; when revenue potential is different – while adjusting pesticide application cost. This is a dynamic tool growers can use to tailor pesticide programs to specific farms and situations.
Sporebuster uses economic models and user inputs indicating soybean sale price, yield potential, and local pesticide program prices to estimate the likelihood of breaking even and average net gain when using the program. Sporebuster is available for iOS and Android.
For more information about fungicides available for white mold management, consult the CPN publication Fungicide Efficacy for Control of Soybean Foliar Diseases (CPN-1019).
Application Timing
Fungicide must be applied at the proper growth stage to maximize efficacy for white mold control. Fungicide applications at the R1 growth stage (beginning of flowering) provide a greater level of control than applications made to soybean at the R3 growth stage (beginning pod). Efficacy of fungicides for white mold management declines greatly after symptom development. Use the Sporecaster smartphone app to assist with fungicide timing decisions. Sporecaster is available for iOS and Android.
Spray Coverage
Adequate plant coverage by a pesticide spray, deep in the soybean canopy where infections start, is important for managing white mold with foliar fungicides. Flat-fan spray nozzles that produce fine to medium droplets (approximately 200-400 microns) provide the best fungicide coverage on sprayed plants. Using higher carrier rates such as 20 GPA can also assist in providing good coverage of the plant by the pesticide spray, especially when the canopy is thick. Follow manufacturers’ recommendations for spray volume and be aware of environmental conditions (such as wind speed) that influence coverage.
Control Expectations
A chemical management strategy does not result in complete control of white mold and, therefore, should be considered only as one component of an integrated management program. Reduction of white mold incidence achieved by fungicides alone in university field trials ranged from zero to approximately 60 percent. Chemical control should be used in addition to using resistant varieties, changing the rotation, integrating cover crops, etc. Do not rely on chemical control alone for white mold management in soybean.
Biological Control
Biological control can also be part of an integrated white mold management program. The fungus Coniothyrium minitans is the most widely available and tested biological control fungus and is commercially available as Contans®. Application of C. minitans should occur a minimum of three months before white mold is likely to develop. Timely applications allow adequate time for the fungus to colonize and degrade sclerotia. Degraded sclerotia will not produce apothecia and, therefore, will not produce ascospores to initiate infection of soybean. C. minitans should be incorporated as thoroughly as possible to a depth of two inches. Avoid additional tillage that can bring non-colonized sclerotia to the soil surface.
There are limited data available on the efficacy of C. minitans for white mold management in soybean. In a few studies, the sclerotia number was reduced by as much as 95 percent and the subsequent white mold incidence was reduced by 10 to almost 70 percent.
Biological control products will not eliminate all sclerotia; fields heavily infested with sclerotia may continue to have disease development until the number of sclerotia in the soil is further reduced. More studies are needed to evaluate the efficacy of biological control products and their potential to reduce white mold of soybean, especially in fields with native populations of biological control fungi.
Daren Mueller
Core white mold management considerations
Maintain records of field history and disease incidence of white mold.
Select soybean varieties carefully:
Use varieties with the best available levels of resistance.
Select the most appropriate maturity group for your region.
Use pathogen-free seed.
Follow good cultural practices:
Reduce plant populations and increase row width.
Rotate with non-host crops (especially small grains)
Consider reduced or no-till practices.
Use cover crops to reduce inoculum density.
Use fungicides properly. They may be warranted in fields with a history of white mold and where the risk of white mold is high. Fungicide application should occur between R1 and R3, before disease develops, for best results.
Consider biological control, which may be valuable as part of a long-term integrated management strategy to reduce sclerotia levels in a field.
Where irrigation is used, reduce frequency during flowering. Ensure irrigation is applied according to soil moisture requirements (i.e. avoid excessive irrigation events).
Earn 0.5 Certified Crop Advisor CEUs after reading this web book. Click here for the quiz.
Disease forecasting and fungicide decision apps
Sporecaster, a white mold forecasting tool for iOS and Android.
Sporebuster, a white mold fungicide decision tool for iOS and Android.
Tools and podcasts
White mold management podcast.
Information and updates
Wisconsin Crop Manager from the University of Wisconsin-Madison
Integrated Crop Management News from Iowa State University
Field Crops from Michigan State University
Pest and Crop Newsletter from Purdue University
Farmdoc from University of Illinois
White Mold (CPN 1005) by CPN
Peer-reviewed manuscripts
Identification of soybean (Glycine max) check lines for evaluating genetic resistance to Sclerotinia stem rot by Webster et al. in Plant Disease. 2021. A Crop Protection Network summary of this article available here.
Meta-analytic and economic approaches for evaluation of pesticide impact on Sclerotinia stem rot control and soybean yield in the North Central U.S. by Willbur et al. in Phytopathology. 2019. A Crop Protection Network summary of this article available here.
Biology, yield loss and control of Sclerotinia stem rot of soybean by Peltier et al. in the Journal of Integrated Pest Management. 2012.
Effects of mowing, seeding rate, and foliar fungicide on soybean Sclerotinia stem rot and yield by Carpenter et al. in Plant Health Progress. 2021.
The complexity of the Sclerotinia sclerotiorum pathosystem in soybean: virulence factors, resistance mechanisms, and their exploitation to control Sclerotinia stem rot by McCaghey et al. in Tropical Plant Pathology. 2018.
An overview of the Sclerotinia sclerotiorum pathosystem in soybean: Impact, fungal biology, and current management strategies by Willbur et al. in Tropical Plant Pathology. 2018.
Spread of Sclerotinia stem rot of soybean from area and point sources of apothecial inoculum by Wegulo et al. in Canadian Journal of Plant Science. 2000.
Earn 0.5 Certified Crop Advisor CEUs after reading this web book. Click here for the quiz.
Daren Mueller
Authors
Damon Smith, University of Wisconsin; Adam Sisson, Iowa State University; Martin Chilvers, Michigan State University; Mehdi Kabbage, University of Wisconsin-Madison; Megan McCaghey, University of California-Davis; and Jamie Willbur, Michigan State University.
Citation
Smith, D., Sisson, A., Chilvers, M., Kabbage, M., McCaghey, M., and Willbur, J. 2022. White Mold of Soybean. Crop Protection Network. CPN 1026. doi.org/10.31274/cpn-20210607-0.
Reviewers
Paul Esker, Pennsylvania State University; Tyler McFeaters; Pennsylvania State University; Karen Luong, Pennsylvania State University; Daren Mueller, Iowa State University; and Albert Tenuta, Ontario Ministry of Food, Agriculture, and Rural Affairs.
References
Allen, T. W., et al. 2017. Soybean yield loss estimates due to diseases in the United States and Ontario, Canada from 2010 to 2014. Plant Health Progress 17:211-222. Article / Google Scholar
Bradley, C.A., et al. 2021. Soybean yield loss estimates due to diseases in the United States and Ontario, Canada from 2015 to 2019. Plant Health Progress. Article / Google Scholar
United States Department of Agriculture National Agricultural Statistics Services (USDA NASS). Https://www.nass.usda.gov/
Sponsors
The authors gratefully acknowledge funding for this project from the North Central Soybean Research Program, the Wisconsin Soybean Marketing Board, and the Michigan Soybean Promotion Committee. This educational resource was made possible by contributions from Iowa State University Integrated Pest Management; the Grain Farmers of Ontario; and the United States Department of Agriculture - National Institute of Food and Agriculture (USDA-NIFA).
This publication was developed by the Crop Protection Network, a multi-state and international collaboration of university/provincial extension specialists and public/ private professionals that provides unbiased, research-based information to farmers and agricultural personnel.
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