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November 15, 2011

White Mold Emerging as Problem for Brazil Soybeans

White mold, which is a disease caused by the sclerotinia fungus, impacted approximately 2.7 million hectares of soybean production in Brazil during the 2010/12 growing season. Under a worst case scenario, the disease could cause yield losses of as much as 40%. The problem seems to be worse at higher elevations in the cerrado regions of central Brazil, but it has also been found in southern Brazil as well.

When the disease is in the process of invading the plant, it develops hard, black sclerotia which can overwinter in the soil for many years making the disease very difficult to control. The disease is extra difficult to control in Brazil because of the multitude of native host plants and the lack of cold temperatures to kill off the disease between growing seasons.

Embrapa organized a task force three years ago to coordinate their research efforts in controlling the disease. The group, which consists of 15 research institutions located throughout Brazil, initiated 12 research sites in the cerrado region to evaluate 10 different fungicide treatments, both commercial and experimental. Some of the experimental chemicals exerted good control of the disease and the Minister of Agriculture has had the chemicals registered for use in soybeans.

Part of the testing program also evaluated the use of biological control for the disease. Some of the initial biological controls had an efficiency of 40% in controlling the disease.

In addition to chemical or biological control, for farmers to be successful in controlling the disease, they need to adjust their management practices to: better manage their crop residue, rotate more frequently to non-susceptible crops, use fungicide seed treatments, use more erect soybean varieties to facilitate fungicide penetration to the bottom part of the plant, select varieties more resistant to the disease, and be careful to thoroughly clean machinery before moving from one field to another to avoid spreading the disease.