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Issue No. 13, Article 4/June 19, 2009

Soybean Rust Update

Thus far in 2009, soybean rust has been observed in five states and 21 counties in the United States and in two states and five municipalities in Mexico. There has been a flurry of soybean rust activity in the last two weeks, with new finds confirmed in Louisiana, Alabama, Georgia, and Florida. Some of these finds were on soybean and others on kudzu.


Current soybean rust observation map of the southeastern U.S. and part of Mexico. Current maps are available at www.sbrusa.net.

Monitoring. Sentinel plots are being used to monitor for soybean rust in North America. These plots, made up of soybean, kudzu patches, or other susceptible hosts (such as yam bean in Mexico), are scouted regularly, generally every week, for soybean rust.

In Illinois, 28 sentinel plots are being established across the state in 2009. University of Illinois Extension educators, research personnel from the University of Illinois and Southern Illinois University, and some industry personnel are involved in collecting leaf samples from the sentinel plots in Illinois and sending those to the University of Illinois Plant Clinic, where the samples are examined microscopically for soybean rust and other diseases.

As data become available from the plots, they are uploaded onto the Integrated Pest Management--Pest Information Platform for Extension and Education (IPM-PIPE) website, where maps are generated that show where soybean rust has been observed in North America (www.sbrusa.net).


Symptoms of soybean rust on a soybean leaflet. Image courtesy Daren Mueller, Iowa State University.


Magnification of soybean rust pustules found on the underside of a soybean leaflet.

Implications for Illinois. Soybean rust has been observed in Illinois every year since 2006. Every confirmation in the state has occurred later in the season (late September and October), so as yet no yield loss has resulted from the disease.

For 2009, the risk of soybean rust in Illinois may be slightly elevated, because many soybean fields have been planted later than normal, with some fields not yet planted. Because soybean rust cannot overwinter in Illinois, spores of the fungus must be moved into the state via weather systems. Even if spores do arrive, the environment must be favorable for infection (frequent rainfall, cloudy weather, heavy dews), and soybean plants must be at a susceptible growth stage (flowering through seed development) for rust to develop and spread.

Management. Currently, the only tool available for managing soybean rust is foliar fungicides. Many products are available to Illinois growers, but not all have equal ability to control soybean rust and other diseases.

A list of registered products available for soybean rust control is published in the updated online version of Using Foliar Fungicides to Manage Soybean Rust, created by soybean pathologists and agronomists from a number of states. The list of registered fungicides for soybean rust control is in Appendix B; information on product efficacy against soybean rust and other foliar diseases is in the chapter titled "Managing Late-Season Soybean Diseases and Soybean Rust: A Southern Perspective."

It is important to know where soybean rust has been observed in North America before making any management decision, so check the soybean rust maps on the IPM-PIPE website regularly. You can also sign up there to receive an e-mail alert when a new soybean rust observation is made.--Carl A. Bradley

Author:
Carl A. Bradley

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