By Jim Isleib,
White mold in Michigan dry edible beans is caused by the pathogen Sclerotinia sclerotiorum. This pathogen is very common and has a number of alternative hosts, including legumes, sunflowers, canola, most vegetables, tobacco, many flowering bedding plants and stone fruits. White mold outbreaks in dry edible beans are worst when a dense crop canopy exists and there is rainy, wet weather prior to, during and immediately after flowering. Losses due to the disease can be severe in crops with high yield potential. Dry beans grown under irrigation are much more likely to have a high incidence of white mold. If white mold is prevalent in a grower’s field, it will be evident now. This is the time to determined what management strategies could be adjusted to minimize the problem in following years.
Using integrated pest management (IPM) concepts is important in developing a strategy to minimize white mold losses in dry beans. Air circulation to allow plants to dry more quickly is an important factor. Wide row planting and proper seed spacing will help with this. Although strong resistance to white mold has not been accomplished through breeding programs yet, resistance varies among dry bean varieties.
Use of fungicide is common to control white mold in irrigated dry beans. In non-irrigated beans, fungicide should be considered if crop canopy is dense and especially if wet weather is experienced about 10 days before and during flowering. The fungus uses deteriorating flowers as a source of nutrients and becomes established during and just after flowering. Small, hard bodies called sclerotia are formed, which can survive in the soil for several years.
Rotation including non-host crops like corn or small grains is important to hamper the build-up of the disease in the soil. Spraying after flowering is not very effective in combatting white mold since the main point of infection is the flower itself. The fungicides currently labeled are preventative, not curative, and do not work well to control the disease once it becomes established.
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