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Indiana, Tennessee join states with Asian soybean rust infections

Indiana officials just announced the state's first soybean rust ever, while Tennessee made the list today with three counties, first rust there since 2004. There are now 13 U.S. states infected with soybean rust in 147 counties and parishes.

Indiana rust may have blown in from Louisiana
The first rust in Indiana was found in Knox County, per an e-mail from and interview with plant pathologist Greg Shaner of Purdue University. That county and later county Posey don't show yet on the U.S. Department of Agriculture's Asian soybean rust monitoring Web site,, due to a technical delay, but it's official.

Shaner says he got word from USDA earlier today that the rust pustule was found last Thursday and sent to the Beltsville Lab for confirmation was indeed Asian soybean rust.

Both counties are in the extreme southwest corner of Indiana, adjacent to rust-positive White County in Illinois and Union County in Kentucky.

Here's the text of Shaner's e-mail sent this afternoon. He's putting a message out on the Purdue soybean rust hotline 866-458-RUST (7878) later today.

"This infection probably arose from the same introduction of spores that infected soybean in several counties in western Kentucky and southeastern Illinois. The rust found in Kentucky, Illinois and Indiana poses no threat to this year’s crop. The disease arrived much too late. Most soybean fields are mature and many have already been harvested. Late-planted soybeans that are still green will be killed by frost before rust has a chance to spread much in them," Shaner says. "Does the arrival of rust in Indiana increase the risk of rust next year? No. The soybean rust fungus can only grow and produce spores in living host plants. Unlike many other disease-causing fungi, rusts cannot survive in crop residue or seed. Once all soybean plants have matured and hard frosts kill any volunteers and kill leaves of kudzu, the fungus will be eradicated here."

While these latest rust discoveries offer no danger to the 2006 soybean crop, much of which is already out of the field, it does demonstrate how quickly and easily rust can move on wind currents.

"Perhaps the most important thing we have learned from the appearance of soybean rust in Kentucky, Illinois and Indiana is that southerly winds can evidently carry viable spores long distances. The disease spread slowly this summer in southern states until late in the season," Shaner says. "A weather-based model for dispersion and deposition of spores of the rust fungus suggests that spores may have been carried from this area into Kentucky, southeastern Illinois, and Indiana from Sept. 22 to 24. If this was the spore dispersal event that gave rise to the infections up here (about two weeks are required for infections to develop into rust pustules), then winds carried spores more than 500 miles before they landed, and these were still viable after this long journey.

"If rust were to develop in the southern Mississippi Valley earlier next summer or in some subsequent year, spores could be carried into Indiana and adjacent states when our soybean crop is still vulnerable."

Rust found in several W. Tennessee fields in three counties
Tennessee officials urge growers to continue to monitor any areas in fields for rust pustules where soybean or kudzu plants still have green leaves.

"Several rain fronts passed by West Tennessee, but they developed and caused rain in Western Kentucky," says UT plant pathologist Melvin Newman. "This may be why soybean rust was recently found in 13 western Kentucky counties while none was found in Tennessee until last week."

In an e-mail to colleagues today, Newman said the very few pustules sighted were "hard to find with a hand lens, but with a low power microscope it was possible. The QuickStix method and polymerase chain reaction (PCR) methods both gave a strong positive reaction for soybean rust.

"On the leaves that were collected on Thursday of last week (Oct. 12), there were 1-10 pustules on every 5-10 leaves that were examined. The pustules were sporulating very profusely and seemed to be very recent infections. No rust was found on kudzu," Newman added.

Newman says some damage is expected to this year's soybeans, but it will be limited in both severity and geographic scope.

"Of course, there will be no real damage to soybeans in Tennessee, but some of the other more Southern states will probably have some damage because they have had rust infections for some time now," he says. "Other counties in Tennessee may have rust infections that we don't know, about so county agents will be submitting samples to me if they can find any green leaves left after the heavy frost on Oct. 13."

Indiana officials just announced the state's first soybean rust ever, while Tennessee made the list today with three counties, first rust there since 2004. There are now 13 U.S. states infected with soybean rust in 147 counties and parishes.

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