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Issue No. 18, Article 6/July 22, 2005

Soybean Rust Update for Illinois

With the recent tropical storms moving up from the southern states, there has been much new concern about soybean rust in Illinois. As of July 15, there were no observations of soybean rust on soybean, kudzu, or pea in Illinois. To our knowledge, spore traps also have not captured any soybean rust spores in Illinois. Although a few presumed soybean rust spores were reported in early July from 1 of 10 traps in Kentucky and in 1 of 10 spore traps in Tennessee, soybean rust has not been found on soybean plants in those states (as of July 15, in spite of extensive scouting and testing). So far in 2005, soybean rust has only been confirmed on soybeans in Alabama, Georgia, and Florida; intense scouting continues in those and other southeastern states.

Hurricane Dennis produced rain and cloud cover throughout Illinois last week. According to the USDA soybean rust forecasting model, spore deposition forecasts show a low potential for significant soybean rust spore deposition in Illinois. This is due in part to the presumed low number of spores being produced in the south on the relatively small areas known to be infected. As of July 15, spraying fungicides for soybean rust management is not recommended in Illinois until soybean rust is confirmed in the state, or possibly in states nearby. It is likely that even if some soybean rust spores were blown recently into Illinois, it will take at least one or two cycles of infection and spore production (each probably 10 to 14 days) plus frequent wet weather conditions before significant disease severity would occur.

The key recommendations are to scout fields frequently and check the Soybean Rust USA Web site for the latest reports and recommendations from Illinois and other states regarding soybean rust. When scouting, look first at the underside of leaves on the lower half of the soybean plants. Look at five plants in 20 different locations in a field. Since soybean rust lesions are small and difficult to diagnose because of similarities with several other leaf pathogens, use a 16X to 20X hand lens. Additional information related to soybean rust in Illinois can be found at the Illinois Soybean Rust Web site and the Illinois Soybean Rust Information Center Web site.--Dean Malvick

Dean Malvick

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