Virginia Tech researchers monitor crop-killing soybean disease
Blacksburg, Va. -- Asian Soybean Rust, an aggressive fungal disease that has caused major yield reductions in the soybean-growing regions of Brazil is being carefully monitored by Virginia Tech scientists and is not expected to cause any major problems in Virginia in 2004.
Scientists at Virginia Tech are taking this new threat seriously, said plant pathologist Erik Stromberg, interim head of the university's department of plant pathology, physiology, and weed science in the College of Agriculture and Life Sciences at Virginia Tech.
Researchers are checking the state's soybean fields, and many agencies are cooperating in a system to warn growers.
Soybeans are an important agricultural product in Virginia. Land planted to soybeans in the state exceeded 500,000 acres in 2004, making it the largest row crop in the state. The most recent official information shows cash receipts of $65.2 million. Strong prices and a potentially high-yielding crop have growers throughout the state looking forward to harvest.
"The disease is still south of the equator, which is a formidable barrier due to high temperatures and ultraviolet light levels," Stromberg said. "Until it gains a foothold in the northern latitudes, I would not expect the disease to move in early enough to cause a problem in Virginia soybeans." David Holshouser, Virginia Tech soybean specialist, said although he is concerned about the effect of soybean rust on Virginia's soybean industry, he's more concerned about the level of anxiety over the disease among farmers.
"This is the most concern over a disease that I've experienced, and this disease is not even present in the U.S.," Holshouser said. "Growers are very aware of the rapid spread and the economic impact that the disease has caused in Brazil. The growers hear of yield being reduced by 80 percent, that the disease can completely defoliate the crop within two or three weeks, and that there isn't enough fungicide to treat all of the U.S. acreage."
"I think that Virginia is as prepared as any state in the U.S.," said Ames Herbert, Virginia Tech entomologist and State Integrated Pest Management coordinator. "We are monitoring for soybean rust in more than 70 fields throughout Virginia on a bi-weekly basis. We have been monitoring fields since June and expect to continue through mid-September when soybeans mature."
The monitoring program is part of work funded by the Virginia Soybean Board, an organization charged with distributing "check-off" funds collected from Virginia producers to conduct research and promote soybeans.
"Virginia's soybean producers did not want to be caught off-guard by soybean rust," said Ronnie Russell, chair of the Virginia Soybean Board. "Dr. Herbert's expertise and experience with monitoring other pests such as corn earworm and soybean aphid led us to request that he include soybean rust in his pest monitoring program."
The soybean rust monitoring program is only one step that Virginia is taking to avert problems with soybean rust. A Virginia Soybean Rust Task Force was formed by Holshouser earlier in the summer and is now drafting a detailed action plan for responding to the threat.
"Our team consists of individuals from Virginia Tech, the Virginia Department of Agricultural and Consumer Services, the Virginia Soybean Association, the Virginia Farm Bureau, the crop protection industry, certified crop advisors, and the insurance industry," Holshouser said. "Our action plan describes our educational goals, the development and certification of a group of 'first detectors,' our pre- and post-confirmation communication plan, and how Virginia will respond once rust is confirmed in Virginia or other parts of the U.S."
Virginia soybean growers need to stay informed about this potential problem, Holshouser said. If any growers suspect there is rust, they should contact the local Virginia Cooperative Extension agriculture and natural resources agent or a certified crop adviser. That person will take a sample of the suspected area to the nearest Virginia Diagnostic Center. If experts suspect rust, the sample will go on to USDA-APHIS for confirmation.
"This past March, Dr. Stromberg and I participated in a 'soybean rust scenario exercise' – a trial run of a communication plan to diagnose soybean rust," Holshouser said. "Within four days after I sent in the mock sample, I received a confirmation. The system works."
Currently, there is no plant resistance to soybean rust, so growers will have to depend initially on fungicides to control the disease. However, research is underway to develop varieties that resist soybean rust.
In actuality, the 80 percent yield reduction is the maximum recorded and is not likely to occur throughout all soybean-producing areas of Virginia or the United States The disease is very dependent on environment, the amount of initial inoculum of the fungus, and the stage that the disease infects the plant.
"The way I see it is that there is one big difference between Virginia's and Brazil's yield loss potential. Brazil maintains a continuous source of the fungus year round. In Brazil, the disease never dies out because there are no freezing temperatures. Virginia's winter freezing will prevent the fungus from over-wintering," Holshouser said.
The lack of freezing temperatures affects soybean rust in a couple of ways. First, the fungus itself survives. Secondly, plants that harbor the disease grow in Brazil year round.
"When I was studying the problem in Brazil last spring," Holshouser said, "I saw soybeans in the seedling stage, soybeans green and producing pods and seeds, and soybeans that were being harvested. In Brazil, the growing season is really spread out. In addition, many areas contain kudzu, an alternative host. Even in areas growing one soybean crop per year, soybean rust will over-winter on the kudzu."
Because the fungus is always present in Brazil, it attacks the crop earlier and has the potential for causing large yield losses. Argentina has not had the same problem with the disease although its acreage is similar to Brazil's. Argentina's climate is similar to America's.
"We don't think that soybean rust will be nearly as devastating as it has been in Brazil," said Pat Phipps, another Virginia Tech plant pathologist. "However, it could still be a future problem for Virginia. It's a manageable problem, but still a problem."
Models have been developed to predict which regions in the U.S. the disease is most likely to first enter and experience rust problems.
"Unfortunately, these models indicate the Mid-Atlantic and southeastern states are at most risk," said Phipps. "Wind patterns, our warm and humid climate, and significant acreage of soybeans and other hosts make Virginia an ideal location for the disease to become established."
Still, all evidence indicates that the fungus will not be able to over winter in Virginia, Phipps said. "This fact will produce a different disease picture for Virginia. This means the fungus must be re-introduced each year by winds from more southern areas of soybean production that border the Caribbean and the southern-most areas of the U.S. Other rust diseases such as peanut rust and corn rust are similar in biology, occur infrequently in our region, and almost never cause significant yield losses."
Source: Eurekalert & othersLast reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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