Allison Tally says she feels sorry for the first farmer who finds soybean rust in the United States. “It will be like a circus,” says Tally. “Police and Homeland Security people will be there because of the terrorist aspects not to mention all the university and chemical company representatives.”
The prospects for notoriety notwithstanding, Tally says farmers need to be vigilant and quick to report disease symptoms because of the importance of early detection and treatment in stopping the spread of soybean rust.
Speaking at a media event in New Orleans, Tally said soybean rust can be devastating — some untreated fields in Zimbabwe lost 80 percent of their yield. But early, effective fungicide programs have kept losses in the 20-percent range.
“The key is acting early to minimize the impact of the disease,” says Tally, who as technical brand manager for fungicides for Syngenta Crop Protection has made numerous trips to Brazil and recently returned from an international soybean rust meeting in Basil, Switzerland.
Soybean rust started in Japan and spread slowly. It was discovered in Paraguay and Brazil in 2001-02 and by 2003-04 was in all of the soybean areas of Brazil. The disease cost Brazilian farmers $600 million in yield and fungicide applications in 2002-03, and, in 2003-04 losses may have exceeded $1 billion.
USDA estimates U.S. losses could be in the range of $640 million to $1.3 billion in the first year and $240 million to $2 billion in subsequent years, depending on the severity and extent of spread.
USDA plant pathologist Roger Magarey has prepared a map of the United States that shows areas where the probability of having at least 15 consecutive days of suitable conditions for the development of soybean rust are highest. Delta states and Missouri, Iowa and Wisconsin figure prominently on the map.
Symptoms start deep in the lower plant canopy and move upward. Farmers will see a yellow mosaic on the leaves followed by a brown, stippled appearance. Leaves turn completely yellow within a few days and brown, reddish pustules appear.
“If the disease occurs late in the season, it is not as effective,” says Tally. “But if it occurs during pod fill, it can be very destructive. Farmers who practice early planting in the South might miss the disease entirely, but soybeans planted behind wheat could get hurt.”
The disease has more than 50 other host plants, including kudzu — no, it won't kill it — which could complicate control in the South. It could overwinter in southern Florida and south Texas and could be spread by southerly winds into the Mid-South and Midwest.
How soon will it reach the United States? Tally believes farmers have two or three more years to prepare. “Once it reaches the United States, it could move from the South into the Midwest because we saw it travel 2,000 miles in Brazil in one season.”