Indiana just announced its first soybean rust ever this afternoon, 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 in Knox, Posey counties 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. That county and later county Posey don't show yet on www.sbrusa.net due to a technical delay, but it's official. Shaner got word from USDA a couple of hours ago that the rust pustule 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 out over the coolbean.info listserv this afternoon and that is now posted online on the Purdue site. He's also putting a message out on the Purdue soybean rust hotline later today: 866-458-RUST (7878).



"Asian soybean rust has reached Indiana. Karen Rane and Gail Ruhl, diagnosticians in Purdue's Plant and Pest Diagnostic Lab, found one rust pustule in a sample of 100 leaflets collected last Thursday by Dan Egel, from late-maturing double-crop soybeans in Knox County. The diagnosis was confirmed by Dr. Mary Palm, a mycologist with the USDA. Early this week, we found a second instance of rust from leaves collected in Posey County by Gibson County Educator Jim True.



"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.



"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.



"In North America the fungus only survives below the frost zone: southern Florida, perhaps along the Gulf Coast, and in northeastern Mexico. Regardless of how far north the disease reaches each year, in the following year the fungus must once again migrate north from its over-wintering sites.



"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. It was not until late August through September that the disease became widespread in the Mississippi Delta. Even then, rust was detected in only a few fields or kudzu patches and was not severe. By late September, rust had not progressed beyond the southern two-thirds of Louisiana.



"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



Per the Tennessee commentary on www.sbrusa.net:



"Asian soybean rust was found in West Tennessee on soybean leaf samples taken from several fields in Gibson, Obion and Weakley counties on Thursday, Oct. 12. After the soybean plants were sampled, a hard frost occurred in West Tennessee, and most remaining green leaf tissue was destroyed.



"The disease samples -- a few rust pustules -- were found on soybean leaves and visually identified with a microscope at the UT Extension lab at Jackson. The samples were then tested with the "QuickStix" method by Dr. Melvin Newman, Department of Entomology and Plant Pathology in Jackson. Final confirmation that the pustules were Asian soybean rust was determined by polymerase chain reaction (PCR) testing in Dr. Kurt Lamour's lab at UT Institute of Agriculture in Knoxville."



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



"UT Extension personnel have monitored for rust in soybean sentinel plots and spore traps across the state all summer and only found these few rust lesions on soybean leaves last week. Dr. Newman speculates that the lack of rain in West Tennessee during critical times in the growing season prevented soybean rust from developing earlier.



"'Several rain fronts passed by West Tennessee, but they developed and caused rain in Western Kentucky," Newman said. "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 also said, "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. 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."



The Tennessee rust announcement new release can be found online. It mentions that there were no rust finds in Tennessee during the 2005 growing season. Asian soybean rust was first found in the United States in November 2004. The disease was confirmed at that time in samples across nine southern states, including one sample from Shelby County, Tenn.



SOURCE: Article on StopSoybeanRust.com based on e-mail from and interview with Greg Shaner, Purdue; e-mail and news release from University of Tennessee, plus www.sbrusa.net.