Posted 23 June 2008. PMN Crop News.
University of Illinois at Urbana-Champaign. aces.illinois.edu
Urbana-Champaign, Illinois (June 5, 2008)--By now it is common knowledge that soybean rust (SBR) was identified in four Illinois counties last fall. Dates of detection ranged from September 25 in Massac County (far southern Illinois) to October 30 in Bureau County. The infected soybean plants were well past the point of yield being impacted by the disease.
Does last fall's occurrence increase the odds of the disease being present in 2008? No, not really. Rust does not overwinter in Illinois and the disease has to re-establish every year from wind-blown spores coming from the southern states. So, the incidence and severity of SBR in areas to the south, wind patterns, regional and local weather, and the growth stage of the soybean are factors involved in the risk of rust moving into northern Illinois.
Soybean plants are most susceptible to rust during growth stage R1 (beginning flower) through R5 (beginning seed). Once plants reach R6 (full seed), yield losses are minimal, the benefits of applying a fungicide are uncertain, and in fact many fungicides have restrictions that do not allow application past R6.
State reports and SBR observations from across the country, including management and strategies for Illinois, are shown on this web site www.sbrusa.net Using foliar fungicides to manage rust are explained at oardc.osu.edu/soyrust