CENTRAL CITY, Neb. (Dow Jones)--Asian soybean rust has been found in Virginia, Arkansas and Indiana, bringing the total number of counties found to be infected with the plant disease to 158, in 15 U.S. states.
The airborne fungus has moved rapidly from the Deep South into the heart of the Corn Belt during the past week, and is now found as far north as Knox County, Ind., just 50 miles south of Terra Haute.
"Perhaps the most important thing we have learned from the appearance of soybean rust in Kentucky, Illinois and Indiana is that southerly winds can carry spores long distances," said PurdueUniversity extension plant pathologist Greg Shaner. "Winds carried these spores more than 500 miles before they landed, and these were still viable after the long journey."
Although Wednesday's discovery was the first ever found in Indiana, Shaner says the airborne fungus poses no threat to the 2006 Indiana soybean harvest, as more than 90% of the crop has already been picked or reached physiological maturity.
Shaner adds that with little green, leafy plant tissue remaining for rust to infect, the disease is unlikely to overwinter into next season as well.
"The soybean rust fungus only survives on living host plants, so here in the temperate region where we have winter and killing frost, it will be eradicated," Shaner said.
In order for soybean rust to return to the Midwest in 2007, he said the spores would need to build up again in regions where no killing frost occurs this winter, allowing spring winds to carry the spores northward.
"So the soybean rust fungus will only survive in North America in the far South - Florida, perhaps along the GulfCoast and maybe northeastern Mexico. It just depends on how far south the frost extends," he said.
This week's Indiana outbreaks occurred in fields of double-crop soybeans and likely originated from spores from infected fields in western Kentucky and southeastern Illinois.
Soybean rust has most recently also been reported in seven counties of eastern Arkansas - Ashley, Chicot, Desha, Jefferson, Lincoln, Lonoke, and Prairie - and in Suffolk and Chesapeake Counties of southeastern Virginia as well.
An infection forecast issued Wednesday by USDA said "all counties close to infected areas in the South - as well as Illinois and Kentucky - are at risk for soybean rust spread, as southerly winds become steady and periods of rainfall enter the area."
Asian soybean rust (Phakopsora pachyrhizi) produces premature defoliation of infected plants and has caused significant crop losses in many soybean-growing regions of the world, and particularly in Brazil. In addition to soybeans, the ASR fungus is able to infect over 30 legumes, including edible bean crops and kudzu. The plant pathogen flourishes in mild, damp, overcast weather.
Source: Gary Wulf, Dow Jones Newswires; Gary.Wulf@dowjones.com