Integrated Crop Management

Soybean rust weekly outlook- May 23

Status of soybean rust.

No other detection has been reported during the past three weeks. The volunteer soybeans found infected in Seminole County of southern Georgia were removed.

Sustained, coordinated, and quality monitoring activities have been carried out in southern states, according to southern region coordinator Don Hershman, extension plant pathologist at the University of Kentucky. Soybeans in sentinel plots in Florida are at flowering stage, but no rust has been reported in soybean plants there.

Disease outlook.

Now we have passed the window for an epidemic that meets the worst-case scenario. In that scenario, Asian soybean rust outbreaks in kudzu plants in Louisiana, Mississippi, or Alabama by the end of May would have resulted in the disease to establish itself in northern soybean production regions before July. Early establishment, not detection, would have created a severe epidemic. However, the northern region is still within the window of possibility for having some outbreaks this summer. The level of possibility depends on the weather in July and August in the North and movement of rust in the South during the next few weeks.

The latest climate outlook by the National Oceanic and Atmospheric Administration (NOAA) shows an above average temperature trend in the South for the months of June, July, and August, which is good news because high temperatures slow rust development. NOAA's outlook also shows a below average precipitation trend from May to June. Our model predicts slow rust development for the upcoming month in the South. Slow rust development in the South means later arrival of the disease in the North.

Asian soybean rust is unlikely to be detected in Iowa before July. (X. B. Yang)

Because soybean rust has not been found beyond Seminole County, Georgia, the anticipated time for first detection in Iowa is very unlikely before July. The anticipated time can be moved beyond early July if no further movement of the rust is detected in the southern region in the next few weeks. It could be earlier if the rust is missed in dense kudzu plants due to lack of experience, a possibility that cannot be ruled out in the first year.

This article originally appeared on page Page 5 of the IC-494(11) -- May 23, 2005 issue.

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