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Around the County

Frequent information updates for agricultural audiences

Soybean Rust in Illinois

Posted by John Fulton -

Soybean Rust Confirmed in Southern Illinois

On September 25, 2007 soybean rust (SBR) was reported and confirmed on a soybean leaflet in Southern Illinois in Massac County. This field is not far from where it was confirmed in Kentucky last Friday. In addition to being found in Illinois, SBR was also confirmed in two counties (Pemiscot and Scott) in southeastern Missouri.

In Illinois, fungicide treatments are not recommended because most soybeans are mature or at a point in their development and growth stage past the time where soybean rust can cause economic yield loss. Soybean plants at growth stages R1 to R5 are the only ones at risk of yield loss from SBR.

However, if a double-crop soybean field is currently at a growth stage prior to R6, it is extremely important to determine the yield potential before considering applying a fungicide. If the decision to apply a fungicide is made, use either a triazole/strobilurin mixture or a triazole fungicide.

Dr. Loretta Ortiz-Ribbing, University of Illinois Extension Specialist in Macomb says, "Many beans in Western Illinois are already stressed by low moisture so their yield potential may already be lower than expected. Applying a fungicide would probably not increase yield potential or be cost effective at this late date especially in areas already stressed by low rainfall."

In addition, many fungicides have preharvest interval restrictions that do not allow application past the R6 growth stage. Any fungicide application requires reading and following the label directions. More information and updated management guidelines are available in the "management toolbox" located in the lower right-hand corner of the main page of the soybean rust pipe website (

In Western Illinois, fields with double-crop beans or any fields where green leaves remain might be a good place to look for soybean rust. Dr. Ortiz-Ribbing suggests to, "Look at the underside of the leaves in the lower canopy of the soybean plant and check to see if you observe any clusters of SBR pustules in small tan or red groupings. A 20X hand lens would be very helpful in this process."

"Even though soybean rust is not an economic problem right now, we would like to continue monitoring it's spread, so we can confirm and verify models used to predict SBR spore movement." Please let Dr. Ortiz-Ribbing know if you think you may have found any suspect leaves.

In addition, any leaves that are suspect for soybean rust should be taken to the nearest Illinois Extension Office. The Digital Distance Diagnostics Imaging (DDDI) system will be used to help evaluate suspicious leaves for soybean rust. Leaf samples can also be sent overnight directly to the University of Illinois Plant Clinic, 1401 W. St. Mary's Road, Urbana, IL 61802 (217-333-0519).

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