With the soybean crop in the midst of its growing season, researchers at Virginia Tech’s College of Agriculture and Life Sciences have begun the painstaking effort to monitor Virginia’s fields for Asian soybean rust.
Asian soybean rust was first detected in the United States in 2004 and most recently was detected in several fields of soybeans in eastern Virginia in 2006.
Fortunately, the disease occurred when the crop was past the point of incurring any significant yield losses from the rust. Soybean rust can reduce yields as much as 50 percent or higher if left untreated when soybeans are at a vulnerable stage of growth.
According to Erik Stromberg, Virginia Tech plant pathologist, producers might not be as lucky this year. “The good news is that the dry weather conditions have not been favorable for soybean rust and the current threat of disease development is low.
The bad news is that growing conditions have not been favorable for soybeans either,” explains Stromberg. The drought conditions that growers have been experiencing across the state have been detrimental to many crops.
Stromberg is quick to point out the situation could change quickly. Weather conditions and wind currents are key factors to the movement and survival of soybean rust spores.
A network of plant pathologists at universities across the United States, in conjunction with the U.S. Department of Agriculture, is monitoring soybean rust movement, weather and wind currents very closely.
A tropical storm or hurricane could accelerate the movement of the rust spores into Virginia and create environmental conditions favorable for development of soybean rust.
The disease has been confirmed in eight Southeastern states in 2007 including Alabama, Louisiana, Florida, Georgia, Mississippi, Texas and most recently, Arkansas and Oklahoma.
Virginia Tech faculty and staff, soybean growers and volunteers began scouting for the disease in early July in commercial fields and in 10 USDA-sentinel plots.
Plant Pathologists Pat Phipps at the Tidewater Agricultural Research and Extension Center and Steve Rideout at the Eastern Shore Agricultural Research and Extension Center are examining leaves from sentinel plots in their part of the Commonwealth.
Stromberg and Diagnosticians Mary Ann Hansen and Elizabeth Bush at Virginia Tech examine leaves from four other USDA-sentinel plots.
The sentinel plots are funded by the USDA and are strategically located to track rust movement throughout the state.
Soybean rust cannot over-winter in areas such as Virginia that experience freezing temperatures. Each year, it migrates northward through air currents.
This year, Virginia researchers, in an effort to track the movement of soybean rust spores into the state, have strategically located spore traps designed to collect spores deposited during rainfall (wet-deposition traps) in addition to spore traps that collect spores that settle out of the atmosphere.
Wet-deposition traps are processed using a nested real-time PCR assay. This method amplifies DNA from soybean rust spores collected in the traps and is extremely sensitive and rapid.
The spore trap monitoring efforts will be used to direct scouting efforts to areas in the state where the spores have been detected, in addition to revealing more information about this wind-borne pathogen.
There are no soybean cultivars with resistance to soybean rust at this time. Therefore, the only defense against this pathogen is fungicides.
Stromberg points out that application timing is critical to effective fungicide treatment. “The sooner we can let growers know that there may be soybean rust in their area, the sooner they can take the appropriate action,” says Stromberg.
There are a number of approved fungicides available to fight soybean rust, but farmers do not want to use them unless necessary. Fungicide treatments can cost growers more than $25 per acre to purchase and apply.
“We are providing soybean growers with disease management recommendations based on the best biological information available,” says Stromberg.
“We are striving to keep farmers from spending money that does not improve the profitability of the crop and to insure that fungicides are used judiciously.”
Growers are encouraged to visit the Virginia Soybean Rust Web site at http://www.ppws.vt.edu/ipm/soybeanrust/index.htm or call the soybean rust hotline (757-657-6450, ext. 130) to receive weekly scouting updates and recommendations.