DECATUR, Ill. (DTN) -- Last fall, you might have noticed an odd looking scab on soybean leaves. A new virus disease, soybean vein necrosis, ramped up this past season. First identified in 2008, the virus has since been spotted in Alabama, Arkansas, Delaware, Kentucky, Kansas, Illinois, Indiana, Maryland, Michigan, Missouri, Mississippi, New York, Ohio, Ontario, Pennsylvania, Tennessee, Virginia and Wisconsin.
The initial symptoms involve small light-green to yellow patches near main leaf veins. As the disease progresses, large, brown blotchy lesions run the direction of the leaf veins. Suzanne Bissonnette, University Illinois plant clinic and Integrated Pest Management coordinator, reports that it looks a bit like the leaf was scratched and the scratch tried to scab over.
"What's alarming is how quickly this virus has spread," Bissonnette told DTN. "At least 98% of the samples we tested in Illinois for it this year were positive. We still aren't sure what that translates to in terms of yield."
Soybean vein necrosis virus (SVNV) is transmitted to the soybean by thrips -- minute insects that feed on the underside of leaves and especially along veins. Dry, hot weather increases the threat of damage. Portions of the plant canopy may be killed in susceptible varieties.
Ioannis Tzanetakis, the University of Arkansas plant pathologist who first identified the virus, told DTN in an interview that the impact of the disease is genotype-dependent. So some soybean varieties are going to be very susceptible and others more tolerant. Scientists are still working to understand the problem.
"Depending on winter conditions, volunteer soybeans or soybeans left standing can be a reservoir for SVNV," said Tzanetakis. "We have also found common weeds can carry the virus.
"The virus presence was much more obvious this year than last," he added. "The environmental conditions seem to play a role, but I'm not sure if it is the drought or the high temperatures."
Pamela Smith can be reached at Pamela.Smith@telventdtn.com
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