For every 10% increase in white mold incidence, there is an estimated reduction in yield of two to five bushels per acre.1 Therefore, timely preventive action is necessary to protect yield in the presence of this disease.
- Common name: White mold
- Scientific name: Sclerotinia sclerotiorum
- Symptoms: The first signs are gray-to-white lesions at nodes. Lesions rapidly spread above and below infected nodes and are often covered in fluffy, white growths.
- Conditions for development: Cool, wet conditions during spring soybean flowering (R1) are ideal for white mold growth. Conditions that increase disease risk also include temperatures below 85 F, frequent rain and relative high humidity.
Fast Facts on White Mold:
- Soybean white mold is an annual threat in the northern United States (north of Interstate 70) from Nebraska to the Atlantic Coast states, though it may appear anywhere when conditions are right.
- Long-term survival structures of white mold, called sclerotia, function much like seeds, protecting the organism until conditions allow it to germinate.
- Sclerotia are dark and irregularly shaped, often resembling mouse droppings.
- Sclerotia allow white mold to survive in the soil for up to 10 years.
- Only sclerotia within 2 inches of the soil surface can germinate. However, tilling infected fields can bring deeper sclerotia to the surface and propagate the disease.
- Soybean plants are most vulnerable to white mold infection during the bloom stage.
- Plant-to-plant infection is possible, but not common. Instead, airborne spores from infected plants land on surrounding plants and use senescing petals as the gateway to infection.
- Diagnosing white mold by foliar damage is not reliable because the signs are similar to other foliar diseases, including stem rot, Phytophthora root rot, sudden death syndrome and stem canker. Stems should be inspected to confirm white mold diagnosis.
Under ideal white mold development conditions, it only takes one soybean crop to jump from 5% or 10% infected soybean plants in a field to 50% the following season. Correct disease diagnosis and implementing an effective management strategy before harvest will help minimize the spread of sclerotia and reduce the risk of severe disease in subsequent years.
These management practices can help:
- Prioritize scouting. Weekly scouting is ideal to check the presence and progression of disease in your fields, especially during key reproductive stages. You’ll want to be in the field during R1-R3 and R4-R5 growth stages, especially if weather conditions favor white mold development.
- Use free phone applications. University of Wisconsin–Madison has developed Sporecaster to forecast disease risk. You enter operation-specific information, then the application will help identify the best timing for disease treatment.
- Time fungicide applications wisely. Most fungicides are very effective for a two-to-three-week period. Timely applications can maximize the value of the application and reduce the need for return applications.
- Select a fast-acting fungicide. Corteva Agriscience offers two soybean fungicides that offer fast-acting white mold control.
- Aproach® fungicide provides uptake in plants nearly twice as fast as competitors, thanks to picoxystrobin. This active ingredient uses four movement properties to quickly surround, penetrate and protect soybean leaves and stems. And when weather and other crop demands make it difficult to time fungicide applications precisely, Aproach compensates with better coverage, preventive and curative activity, and residual control.
- Viatude™ fungicide is a new white mold control solution for northern U.S. soybean farmers. Viatude has the same proven disease control and performance of Onmira™ active found in Aproach fungicide that farmers have come to rely on, plus prothioconazole for added white mold protection, strong plant health and higher yield potential at harvest.
- Note: Viatude can be paired with Aproach in a two-pass system for even stronger plant health throughout the season. A program approach with two fungicide passes, along with other Integrated Pest Management practices, can help prevent disease resistance from developing.
- Choose resistant hybrids. Your customers may want to consider hybrid or variety selection as a first step in disease prevention next season.
- Harvest any infected fields last. Thoroughly clean equipment after leaving an infected field.
- Rotate with a nonhost crop to reduce disease pressure in a field. More than one year away from soybeans may be required to reduce white mold problems, depending on soybean tolerance, field history and other factors. Nonhost crops include corn, sorghum and small grains. Susceptible crops to avoid in a rotation include alfalfa, clover, sunflower, canola, edible beans and potatoes.
Consult your local Corteva Agriscience representative and check out our Corn & Soybean Disease ID Guide for more detailed management recommendations for white mold and common Midwest crop diseases.
1 White Mold (Sclerotinia Stem Rot) of Soybean. South Dakota State University Extension. https://extension.sdstate.edu/white-mold-sclerotinia-stem-rot-soybean
Aproach®, Aproach® Prima and Viatude™ are not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. Always read and follow label directions.