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Issue No. 23, Article 7/October 9, 2009

Soybean Rust Confirmed in Thirteen Illinois Counties So Far in 2009

Every year since 2006, soybean rust has made its way into Illinois late in the growing season. Soybean rust was confirmed late last week in Illinois. The first two confirmations came from samples collected from soybean fields in Johnson and Massac counties; Alexander, Gallatin, Hardin, Jackson, McDonough, Pope, Pulaski, Saline, Union, White, and Williamson counties soon followed. For the most up-to-date distribution of soybean rust in Illinois and North America, go to the IPM PIPE Soybean Rust website (www.sbrusa.net).

Soybean rust found this late in the season should have no impact on soybean yields in Illinois this year; however, we were only a few weeks from having potential problems in a few late-planted double-crop fields in the very southern portion of the state. More than a few double-crop soybean fields in southern Illinois are still very green, but they are at or past the R5 (beginning seed) developmental stage. Most of the research on soybean rust in the U.S. and South America has shown that plants are most susceptible to rust and yield loss between the R1 (beginning flower) and R5 stages of development; fields in Illinois thus should be in the clear now.

Finding soybean rust in Illinois this year will have no impact on the risk for next year, although it does show that the pathogen is very capable of making it this far north. Will this pattern of late-season soybean rust always hold true for Illinois? Unfortunately, it may not. Soybean rust is still in its infancy in the U.S.--we are still experiencing it only a few years after its first introduction into North America. The pathogen is very capable of adapting, and it is likely that every year it will adapt better to surviving on the kudzu biotypes in the southern U.S. If this happens, the potential for rust's appearing earlier in the southern states will be present, which would mean a larger build-up of rust spores earlier in the season. A scenario like this would certainly put the Midwest at greater risk, depending on the presence of storm systems to push the spores northward and on local weather conditions.

Soybean rust pustules on the underside of a soybean leaflet (magnified).

Close-up of soybean rust pustules with spores exuding from the pustule (magnified).

It is likely that soybean rust is currently present in more than 13 counties in Illinois and that additional counties will be confirmed before the season is over. To be alerted when Illinois counties become positive, you can sign up for e-mail alerts at the IPM PIPE website.--Carl A. Bradley

Carl A. Bradley

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