Management Recommendations for Soybean Fields Infested With White Mold

This summer’s cool and wet weather has created ideal conditions for the development of white mold and the disease is now showing up in soybean fields across Michigan. There are no management practices that can be implemented at this point in the growing season for reducing the incidence and severity of white mold in the 2014 soybean crop. However, producers can significantly reduce the amount of inoculum available to infect future susceptible crops grown in the infested fields.

White mold inoculum is contained in small black survival structures called sclerotia. The sclerotia are produced on and in the stems and pods of infected plants and resemble rat droppings. Sclerotia can germinate at the soil surface and up to a depth of 2 inches under favorable conditions. However, they can survive for five to seven years when incorporated deeper in the soil with tillage operations. Sclerotia management should be the focus for managing white mold at this stage in the growing season.

Keeping long-term field records is the first step to managing white mold. Identify heavily infested fields and record the variety, planting population, planting date, fertilizer applications, irrigation timing and rates, and row spacing for each of these fields. This information will help you track fields having the most potential to develop white mold and identify management practices that can be changed to reduce white mold pressure in future soybean crops.

Tillage can be an important method for managing sclerotia, and crop rotation plans should be considered when making tillage decisions in severely infested fields. No-tillage is recommended when the next crop is not susceptible to white mold. With no-tillage, all of the sclerotia produced by this year’s infestation will remain on the soil surface where they have the highest probability of germinating. When the sclerotia germinate in fields planted to a non-host crop, no infection occurs and the lifecycle of the disease is terminated. Non-host crops vary in their ability to create favorable conditions for sclerotia germination. Information from Wisconsin showed that small grains produced a higher level of sclerotia germination than commercial corn and information from IowaStateUniversity states that seed corn does not produce conditions favorable for sclerotia germination.
Tillage is recommended if the following crop is susceptible to white mold. Tillage operations will bury the sclerotia more than 2 inches deep, reducing the quantity of inoculum available to infect the succeeding crop. However, the sclerotia will remain viable for at least five years and will be returned to the top 2 inches with subsequent tillage operations where they can germinate and infect susceptible crops.
Producers can reduce the movement of sclerotia to non-infested fields by harvesting infested fields last and thoroughly cleaning the combine before entering non-infested fields and when soybean harvest is completed.
Producers may consider applying a biological control product such as Contans or KONI to fields having a history of severe white mold. These products contain 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 2 inches at least three months prior to initial soybean bloom. Fall applications of 2 pounds per acre have been the most effective for reducing the number viable sclerotia in the soil. It is important to note that Contans and KONI will attack and degrade the sclerotia in only the top 2 inches of soil. Tillage operations deeper than this should be avoided to prevent redistributing viable sclerotia into the top 2 inches where they can germinate and infect the succeeding susceptible crop.
While there is nothing that can be done at this time to reduce the effects of white mold in this year’s soybean crop, producers can reduce the amount of inoculum available to infect susceptible crops grown in the future.

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