Begin Managing White Mold In Soybeans This Spring

 

 

 

 

White mold can be damaging for soybeans, and farmers should consider implementing management practices this spring in fields prone to the disease.

 

Soybean farmers should use an integrated approach to white mold management, and some of the most effective practices are implemented in the spring. The key is to select practices that have been proven to reduce white mold if it occurs but will not reduce yields significantly if environmental conditions don’t favor white mold.

 

When managing white mold, it is helpful to understand the principles of the disease triangle:

 

White mold disease only occurs when all three factors come together. By altering any of the three, farmers can influence disease development. Ways to alter the triangle include variety selection, affecting canopy microclimate through planting rate and row width and managing the pathogen itself.

 

Varieties vary significantly in their susceptibility to white mold, and planting the most resistant varieties in fields prone to white mold is a key management practice. All seed company catalogs provide relative white mold ratings for the varieties they offer. These ratings provide valuable information when comparing varieties from a given seed company. However, they are less useful for comparing the level of white mold tolerance among varieties from different companies.

 

Selecting varieties that resist lodging and have a narrower canopy width can also reduce the incidence and severity of white mold. Planting varieties from a range of maturity groups may help some fields avoid severe white mold infestations by staggering the susceptible flowering period. This occurred in 2014 in Michigan, when the early-maturing varieties tended to avoid white mold infection and development.

 

Reducing planting rates can reduce white mold incidence by decreasing the potential for lodging and plant-to-plant spread of the disease. Most agronomists agree that a harvest population of 100,000 uniformly-spaced plants per acre will maximize economic returns, even in the absence of white mold. This would be a reasonable target to aim for in fields having a high potential to develop white mold. There are many factors that determine soybean germination and emergence, and farmers should account for these when reducing planting rates.

 

Emerson Nafziger and Dennis Bowman at the University of Illinois developed an excellent soybean planting rate calculator. It allows users to fine-tune planting rates by entering the final stand they want to achieve and adjusting germination and emergence percentages for seed quality and planting conditions.

 

Rows greater than 20 inches wide can decrease the threat of white mold but may not always lead to a yield increase. University row-spacing trials have shown 30-inch rows reduce soybean yields by approximately three bushels per acre when compared with 15-inch rows.

 

Applications of nitrogen fertilizers or manure have been shown to increase early plant growth and canopy closure, creating favorable conditions for developing white mold. Therefore, nitrogen fertilizer and manure applications should be avoided in fields with a history of the disease. Nitrogen fertilizer applications to soybeans are rarely profitable anyway, making this the easiest practice to implement.

 

Farmers may also consider applying a biological control product, such as Contans  to fields with a history of severe white mold. Contans contains Coniothyrium minitans, a naturally-occurring fungus that attacks and degrades sclerotia in the soil. The products should be incorporated into the soil as uniformly as possible to a depth of two inches, at least three months prior to initial soybean bloom.