Chemically Speaking - July 2006

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Asian Soybean Rust Living Up to Name

Asian soybean rust (ASR) has been confirmed in three groups of sentinel soybeans planted in Martin County, Florida, as of June 16.  This is the first occurrence of ASR on soybeans planted this season anywhere in the U.S.  Carrie Harmon of the Southern Plant Diagnostic Network at the University of Florida stated that while this infection is not going to have a major impact on inoculum levels in the state, given how much lower those levels are compared to 2005 at this time - it is the first positive ASR find in the United States since it was found on March 2, 2006, in Miller County, Georgia.  By the 10th of July, it was noted in soybeans in Decatur County, Georgia, which is on the border of Florida. 

However, the results of several experiments have questioned the validity of other hosts of ASR.  Snap peas, while listed as a host crop, did not develop symptoms or test positive for ASR even when interplanted with soybeans that developed significant disease symptoms, says University of Georgia extension vegetable pathologist David Langston in Tifton.  A similar trial that involved side-by-side rows of soybeans and snap beans yielded comparable results. 

Jim Marois at the UF/IFAS North Florida Research and Education Center in Quincy demonstrated in 2005 that a collection of legumes that included snap bean, kidney bean and runner bean could be infected naturally with ASR, but the disease has yet to be found in commercial non-soybean bean fields in the state.  “I think what we’re going to find is that other bean crops will not be affected by it very much.  A lot of the time, they are already being sprayed with fungicides to control common bean rust.  I would expect anything you are doing to control common rust will control soybean rust.”  said Marois.  (ProMED-mail posts 6/16/06 & 7/11/06, and The Grower, July 2006).