Cool, wet conditions. That is what has delayed planting in Iowa. These are also the conditions that favor the development of Asian soybean rust (SBR). Don't worry, current conditions do not make it more likely for rust to appear in Iowa this year. The causal agent, Phakopsora pachyrhizi, cannot overwinter in the Midwest. In order to infect Midwestern soybeans, viable spores must be blown from southern Florida or Texas and arrive when there are cool, moist conditions.
Iowa State University
von Qualen, Ralph and Yang, Xiao-Bing, "2007 soybean rust sentinel plots" (2007). Integrated Crop Management News. 1076.
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