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White Mold Mushrooms Show Up

By XB Yang, SS Navi and Linus Li, Department of Plant Pathology

Over the last 10 days the weather was favorable for the production of soybean white mold mushrooms in Iowa. Yesterday we visited fields near Clear Lake in north central Iowa with crop consultant Dan Muff and found abundant white mold mushrooms in a continuous soybean field, which had a closed canopy with wonderful growth. The density of the mushrooms was very high, 3 apothecia/square foot, and soybean plants are likely to be infected.  The early showing in such a large number in this field was due to early planting, good growth and a higher number of sclerotia from last year. According to Dan, this field had very bad white mold and this year it was planted April 29. 

white mold mushroom

  Photo credit: SS Navi and XB Yang

The level of soybean white mold occurrence this year is likely to be less than last year, because last year we had a record cool July. Statistically, the chance to have two years in a row with record cool temperatures is unlikely, although early July in this season has been cool and wet in Iowa. Because white mold can continue to attack soybean in August, the weather conditions in part of August are also factors that impact the outbreak of soybean white mold. The risk of white mold varies from field to field, in addition to flowering weather conditions. The field we visited was planted April 29, had early canopy closure and was loaded with sclerotia, representing a high-risk situation. If white mold risk is high in your field, consider using a fungicide to protect your soybean.  See our previous article on white mold control for chemical information.

white mold mushroom

  Photo credit: SS Navi and XB Yang

We also found many white mold mushrooms in a cornfield. Rotation with corn to promote white mold mushroom production is a good measure to reduce white mold risk for next year’s soybean. However, white mold spores produced in a cornfield can travel up to 45 yards, with most infected plants in areas adjacent to the cornfield, according to a study from our lab in 1995. The study was done in two locations, one in Humboldt and one near Ames. For the field at Ames, spores traveled further. When white mold spores land on soybean plants that are flowering and environmental conditions are right, they can infect soybean plants. The effects on soybean yield by spores from cornfields are yet to be determined. These infected plants, however, produce sclerotia, which are the source of future infections. This presents a challenge: how to balance management practices of using corn rotation to reduce white mold risk.


XB Yang is a professor of plant pathology with research and extension responsibilities in soybean diseases. Yang can be reached at (515) 294-8826 or by emailing xbyang@iastate.edu.

 


This article was published originally on 7/8/2010 The information contained within the article may or may not be up to date depending on when you are accessing the information.


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