Soybean Rust Update

Bob Mulrooney, Extension Plant Pathologist;

Since January of 2008, soybean rust has been reported in four counties in Alabama; six counties in Georgia, 18 counties in Florida; four counties in Louisiana; three counties in Mississippi, and five counties in Texas. Rust was also reported in three states (five municipalities) in Mexico on yam bean and soybean. These were destroyed or are no longer active. Recent and upcoming hurricane disturbances are likely to move spores northward.

In DE soybean maturity ranges all over the board with the Group III varieties almost mature in many areas. Most of the non-irrigated double crop beans are very small and have not formed a canopy which would be unfavorable for soybean rust. Once soybeans reach R6 (full seed development) they are not affected by soybean rust. Most of the crop will be in the later growth stages in 3-4 weeks and again would be unaffected by SBR. The soybean rust fungus is beginning to show up now in a few commercial fields in FL, and GA which was predicted several weeks after Hurricane Fay hit the area. Weather in the Gulf Region will continue to be favorable for infection and sporulation due to the aftermath of Hurricane Gustav and now Hanna on its heels. There still is not much soybean acreage infected but kudzu infections are increasing as well. It is hard to predict if there are enough spores in the South to have much impact if a significant transport event occurs like Hurricane Hanna might provide. The other ingredient to add to the mix is that many of the GA producers and now SC growers have sprayed their soybeans with fungicides for other diseases and may spray specifically for rust if they think they are at risk. This protects their crops and does not provide added spores for transport north. There is a very low risk of rust appearing on late maturing full season irrigated soybeans and possibly some irrigated double crop soybeans after wheat or barley, but as stated earlier it would in all likelihood occur too late to affect yield. Spraying is not recommended.

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