|Disease: White Mold|
Your Soybean Checkoff.
Start with recordkeeping
Taking accurate notes about where and how much white mold occurs in each soybean field is important for future management planning. Tracking disease levels across years also will help determine the potential sclerotia load (inoculum) that may be present in a particular field.
Recording disease and yield performance for different varieties will help in future variety selection for field with a history of white mold.
No soybean variety is completely resistant to white mold, but partially resistant varieties are available. A partially resistant variety has significantly less disease incidence than a susceptible variety, but some disease occurs when conditions are conducive. Avoid planting highly susceptible varieties in fields with a history of white mold.
Variety selection should be based on resistance ratings determined across multiple locations and multiple years. Check with seed dealers and local Extension for date that include varietal responses to white mold. Consider that testing conditions and scoring methods vary within the seed industry.
Short crop rotations, such as a soybean-corn rotation, will eventually lead to a build up of sclerotia in the field. A minimum of two or three years of a non-host crop, such as corn or small grains (wheat, barley or oats) can reduce the number of sclerotia in the soul. Most sclerotia die over a three- to four-year period between soybean crops.
Forage legumes, such as alfalfa and clovers, are less susceptible to infection but still can be infected by S. sclerotiorum.
Soybean fields with a history of white mold should not be in two or three year rotations with other crops susceptible to white mold. These include edible beans, canola, cole crops (cabbage, broccoli) pulse crops (peas, chickpeas and lentils), sunflowers and potatoes.
The impact of tillage on white mold development is inconsistent, although several studies have indicated lower levels of disease in no-till.
Deep tillage may initially reduce white mold incidence by removing sclerotia from the upper profile which may reduce the number of apothecia produced. However, sclerotia can remain viable for more than three years if buried 8 to 10 inches in the soil, and may be returned to the soil surface in subsequent tillage operations.
Although more sclerotia are found near the soil surface in no-till systems, they may degrade faster in these soils compared to tilled soils.
Early planting, narrow row width, high plant populations, and high soil fertility all acclerate canopy closure and favor disease potential. However, modifying these practices may reduce yield potential.
Many weeds are also hosts of S. sclerotiorum. See Management of White Mold in Soybean for a list of common examples.
Avoid excessive irrigation until after flowering. Low moisture levels are critical for reducing the potential for apothecia formation and white mold development. Infrequent, heavy watering is better than light, frequent watering.
Fungicides may be warranted in fields with a history of white mold and where the risk of white mold is high, but they should be applied at R1 for best results. See Management of White Mold in Soybean for a list of currently registered fungcides, timing, coverage, and control expectations.
Biological control may be valuable as a long-term strategy to reduce sclerotia in a field. The fungus Coniothyrium minitans is the most widely available and tested biological control fungus for managing white mold. See discussion in Management of White Mold in Soybean.