No. 20 Article 8/August 10, 2007

Soybean Rust Update

Soybean rust was detected in northern Oklahoma earlier this week. Oklahoma and Arkansas are the two most northern states in which soybean rust has been detected so far in 2007. The soybean rust forecast for the next few days from the Pest Information Platform for Extension and Education (PIPE) Web site is predicting that "soybean rust spores could be transported as far north as Iowa and Illinois, but the likelihood of the spores surviving is minimal."


Distribution of soybean rust in North America on August 7, 2007. From the PIPE Web site.

What does this mean for Illinois soybean growers? Growers should continue to follow the progress of soybean rust in the U.S. using the PIPE Web site and continue to have suspicious leaves diagnosed through the University of Illinois Distance Diagnostics through Digital Imaging system (see ipm.uiuc.edu/bulletin/article.php?id=792 for instructions) or the University of Illinois Plant Clinic. Soybean plants are most susceptible to rust during stages R1 (beginning flower) through R5 (beginning seed). Once plants reach R6 (full seed), yield losses are minimal, and many fungicides have restrictions that do not allow applications past R5. Some soybean fields in the state are approaching R6, and many more will be at R6 in a few weeks.--Carl A. Bradley

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