Soybean School: The Increasing Threat of White Mould


Each disease threat is unique. Some pathogens are carried on wind or insects, others live in the soil and some reside on crop residue. The expected pressure of a disease for next year is largely dependent on how a disease is spread — those that winter in the soil or on residue are the most likely to become increasing threats, year over year, if conditions are favourable and crop rotations are tight.

White mould, also called sclerotinia, is a disease of soybeans, edible beans, canola and more, and overwinters as sclerotia in the soil. There are hard, black seed-like structures that can persist in the soil for up to 10 years. These sclerotia become a mushroom-like structure in the spring and summer, releasing thousands of new spores to infect a susceptible plant in the growing season. Nasty things, indeed.

Horst Bohner, soybean specialist with the Ontario Ministry of Agriculture and Food, says that the increased white mould incidence throughout much of Ontario in 2013 is an early warning sign to farmers for 2014 management and beyond. While disease development is largely tied to the weather in-season, keeping tabs on the inoculum levels in fields is a good first step in determining which fields may need closer monitoring, a less-dense plant stand (or wider rows), a potential fungicide pass or a tolerant variety.

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