"Fortunately for our soybean producers in Virginia, this year's crop is out of danger," said David Holshouser, associate professor and Extension soybean specialist. "Once soybean seeds reach their full size in the pod, the crop will mature before rust affects a significant amount of leaf surface. Our May-planted crop is now being or is close to being harvested. Those soybeans planted after small grains are well on their way to maturity and should not be affected either," asserted Holshouser. Therefore, the likelihood of soybean rust reducing the Virginia yield in 2006 is almost nonexistent.
This is the first identification of the disease in Virginia since Asian Soybean Rust was first detected in the United States in 2004. The disease, which extensively reduced soybean yields in Brazil, has been confirmed this year in 15 states, including Louisiana, Florida, South Carolina, North Carolina, Georgia, Alabama, Kentucky, Texas, Illinois, Mississippi, Missouri, Indiana, Tennessee, Arkansas, and Virginia.
Visual detection was part of the weekly scouting routine conducted at various locations across the state by Virginia Tech faculty and staff, soybean growers, and volunteers.
Pat Phipps, Virginia Tech plant pathologist at the Tidewater Agricultural Research and Extension Center in Suffolk, Va., examined the suspect leaves collected in Chesapeake and Suffolk under a high-power stereoscope and noticed some rust-like pustules on the leaves.
"Without the stereoscope, I would have never been able to detect the fruiting bodies," said Phipps. Not only did the detection of the disease require microscopic observation, the incidence was very low. "The Chesapeake sample of 100-plus leaflets showed only seven leaflets with pustules, which ranged from one per leaflet up to seven or eight on one leaflet," said Phipps. "Most (in the Chesapeake sample) had either one or two pustules. The Suffolk sample of 100-plus leaflets had pustules on only two leaflets; two on one leaflet and one on another leaflet."
Samples were sent overnight on October 16 to the USDA laboratory in Beltsville, Md., to confirm his suspicion. Phipps also ran an immunoassay test, commonly referred to as an ELISA test. This test was positive for presence of soybean rust. A positive confirmation was received from the lab in Maryland on October 18.
Although Virginia's soybean crop is out of danger, scouting for the disease continues.
"There is still much to learn about this disease. Ideally, we would like to be able to predict where the disease will occur and how severe it will be," emphasized Erik Stromberg, Virginia Tech plant pathologist located in Blacksburg. Models are currently being developed to do this and the data provided by Virginia and other states will be used to validate the accuracy of those models.
"Our goal in the few remaining weeks of this growing season will be to sample double-cropped soybeans for rust in other counties to determine the scope of incidence," said Phipps. "These data along with hourly environmental data from our weather network should be very helpful in understanding the epidemiology of soybean rust this year and developing predictive models for the future."
According to Stomberg, the pathogen will not overwinter in Virginia. It can only survive on a live host. He believes that it is likely that it will overwinter along the Gulf Coast in kudzu, and perhaps volunteer soybeans, and it is likely that it will survive in the Caribbean and Mexico.
The farm-gate value of soybeans in Virginia has ranged from $75 million to $100 million annually. Several years ago when the danger from Asian Soybean Rust became imminent, Virginia agriculture leaders formed the Soybean Rust Task Force. It created a plan that includes educational programs for Virginia Cooperative Extension agents, crop advisers, growers, and others to understand what the disease looks like and what action to take if it is found. It established a monitoring system to identify soybean rust as well as the soybean aphid, also a major problem.
In addition, Virginia Tech has established the Virginia Soybean Rust website at: www.ppws.vt.edu/ipm/soybeanrust/index.htm and a phone hotline where growers and agribusiness can get weekly updates and recommendations.
Dick Atkinson, executive director of the Virginia Soybean Association, summarizes, "These programs have provided Virginia growers with a peace of mind in knowing that we are out there actively looking and won't let these pests sneak up on us. Although our recent discovery will not affect this year's crop, it does prove that our scouting efforts were effective in detecting a very low level of a potentially destructive pest. And detecting a disease such as soybean rust at this low level is important in keeping Virginia's yields up and maintaining a strong and healthy industry."
Lori Greiner | EurekAlert!
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