University of Nebraska-Lincoln Extension, Institute of Agriculture and Natural Resources

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August 11, 2006

Spread of soybean rust limited in 2006

Current distribution of confirmed soybean rust in the United States (red areas) and scouted areas (green) as of August 8, 2006. (Source: USDA Soybean Rust Web site at sbrusa.net).

Extremely dry and hot conditions across much of the southeastern United States have resulted in very limited development of soybean rust this year. Growers and researchers across the United States were on the lookout for soybean rust, but it never developed beyond the southeast. Earlier in the season there was more inoculum across the southeast than in 2005; however, this has not developed into more rust this year. In Texas, where dry conditions have prevailed through much of the growing season, there have been no confirmed cases of rust. Historical weather patterns suggest that spores would likely travel up from Texas over the Central Plains to reach Nebraska fields.

Observations on soybean rust and where it is currently occurring can be found on the USDA soybean rust web site at: SBRUSA.NET. This year several tools have been added to the web site to help with documentation for crop insurance purposes. This site continues to be a collaborative project with land grant universities, USDA scientists and the soybean checkoff. Throughout the season we have been monitoring soybean rust sentinel plots at 26 Nebraska locations. While many other foliar diseases have been observed in these plots, we have not found soybean rust.

In addition to sentinel plots there are also two soybean rust spore traps in Nebraska. We did detect soybean rust-like spores on July 21 in the eastern part of the state near Nebraska City. We also have a spore trap near Clay Center which hasn’t had any soybean rust spores to date. The spore find in the eastern edge of the state suggests spore movement from the gulf state areas. The positive spore trap find demonstrates the ability of airborne rust to move great distances and shows us how rust could have moved around the world; however, we have not seen soybean rust develop in most of the U.S. areas where there have been spore trap finds.

We do not recommend any action based on the spore trap finds since we cannot confirm that they are soybean rust or that the spores were viable. As many soybean fields are in the mid-reproductive stages at this time, we should not see soybean rust affecting production this year. We will continue to monitor for the disease and track its development.

Loren J. Giesler
Extension Plant Pathologist

Copyright 2006 by the University of Nebraska Board of Regents. All rights reserved.

Published by University of Nebraska-Lincoln Extension in the Institute of Agriculture and Natural Resources Cooperating with the counties and the U.S. Department of Agriculture.

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