Corn and Soybean Management
Soybean Rust: Answers to Common Questions (24 November, 2004)
Soybean rust is serious threat to soybean production in the US. Soybean rust has been lurking south of the border for several years now, and was reported for the first time in North America earlier this month. Since this initial finding in Louisiana the disease has been reported the several additional southern states. The weather during the growing season appears to be favorable for disease development in most areas of the US and the USDA is estimating that the disease is capable of reducing yields by 10–80%. Total losses the first year may approach $1.3 billion. The management of soybean rust will be not be simple. The USDA has evaluated all soybean varieties currently grown in the country and found only limited levels of natural resistance to the disease. The first line of defense against soybean rust is likely to be carefully timed fungicide applications.
The implications of soybean rust for Pennsylvania are not completely clear. However, based on recent research and other resources we may be able to answer some common questions about soybean rust.
What other crops might be affected by soybean rust?
The fungus that causes soybean rust has many different host plants including soybeans, green beans, dry edible beans, sweet clover, and kudzu. At this point we know that soybeans and kudzu can be severely diseased and support large amounts of reproduction by the fungus. The degree to which other hosts will become infected and allow reproduction remains unclear. In fact, disease severity and reproduction levels will likely vary with specific variety of a given crop. Kudzu is an important host because it may play a role in where the fungus survives in North America.
Will the Fungus that causes soybean rust survive in Pennsylvania?
No, based on recent research by Iowa State University it does not appear that the fungus will survive the winter in Pennsylvania. However, the fungus is likely to survive in southern states where mild winter conditions allow survival of the fungus and allow kudzu to remain green all year.
How could soybean rust spread to Pennsylvania?
The fungus that causes soybean rust is thought to be moved great distances by wind, and it is possible that soybean rust will be moved by wind from southern states where the fungus survives the winter into northern states each season. The timing of these migrations relative to soybean development will have a great impact on how we manage soybean rust here in PA. For example, if rust arrives early in a growing season, and weather conditions favor disease development we may have to use multiple fungicide applications to control the disease. However, if the disease is not moved into the area by wind currents, or arrives late in a growing season then no fungicides will be required.
What has been done in Pennsylvania to prepare?
The Pennsylvania Department of Agriculture and Penn State have joined with many soybean producing states and applied for “section 18” status for fungicides not currently labeled for application soybeans. About half of these requests have been approved by the EPA, and we are hopeful the remaining requests will be processed quickly. This means that soybean producers in the commonwealth will have access to these additional tools if they are needed next season. Penn State Extension Plant Pathologist, Dr. Erick DeWolf has been working with disease specialists in other states to develop resources that can help producers identify the disease and refresh their knowledge of fungicide use. These resources should be available during the next few months and will be distributed by Penn State Extension. Current Penn State resources are available on-line at http://cornandsoybeans.psu.edu/
Dr. Erick De Wolf
Department of Plant Pathology
The
Pennsylvania State University
Crop Management Extension Group (CMEG)
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