SALEM, Ohio – The USDA’s Animal Plant Health Inspection Service reported that Asian soybean rust (Phakopsora pachyrhizi) was found on soybean leaf samples collected from two research plots near Baton Rouge, La.
This is the first confirmed report of the fungus in the contiguous United States.
Aggressive fungus. The presence of the disease in other countries, such as Brazil, has caused significant yield losses and high fungicide costs. There are concerns that the disease could present similar issues for U.S. growers.
Soybean rust is an aggressive fungus similar to the rust fungi that cause wheat leaf rust and corn leaf rust. It poses no health risk to humans or animals.
In the field. Soybean rust attacks the foliage of soybean plants causing the leaves to drop early, which inhibits pod setting and reduces yield.
Host plants infected with soybean rust first exhibit small lesions that gradually increase in size and turn from gray to tan or brown.
Once lesions appear, defoliation is rapid, resulting in fewer pods, fewer seeds per pod, lower seed weight and early plant maturity.
No resistant varieties. “There are currently no rust-resistant or tolerant soybean varieties,” said American Soybean Association President Neal Bredehoeft. “Research is ongoing, but such varieties still are five to 10 years away.”
Bredehoeft said fungicide treatments currently represent the only option for containing soybean rust by lessening the spread of spores.
Don’t rush purchases. Anne Dorrance, an Ohio State University plant pathologist with the Ohio Agricultural Research and Development Center, said this is not the time for growers to rush out and stock up on fungicides.
“The thing that we’ve learned from other countries is that this disease is manageable with fungicides, but there are still many questions that need to be answered,” said Dorrance.
“Questions such as will the disease survive and overwinter and which fungicides are the most cost-effective. Growers should go and enjoy the holidays and by January we should have a lot of these questions answered.”
Other hosts. Soybean rust can infect a variety of other legumes that could serve as an inoculum reservoir with potential for winter carryover. In addition to soybeans, there are also more than 100 other plant species reported to be hosts for soybean in nature.
What’s registered? Currently, there are registered fungicides that work well against soybean rust and U.S. Environmental Protection Agency Section 18 Quarantine Exemption requests have been submitted by several states to expand the number of fungicides available. Ohio is one that has submitted a request.
The products, however, are expensive; Ohio State researchers are currently studying ways to help producers save on application costs.
Ohio State plant pathologists, the Ohio Department of Agriculture, and the USDA Plant Protection and Quarantine have drafted a management plan to combat the spread of soybean rust.
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