Asian rust spreads to more states

In mid-November, with Louisiana and Mississippi having confirmed Asian soybean rust within their borders, scout teams and researchers fanned out across the South to see how far the wind-borne disease had spread. It didn't take long to add more states to the list of infected.

Nov. 19 the USDA confirmed soybean rust had been found in Florida, Georgia and Alabama.

“When I heard Louisiana had confirmed soybean rust I thought, ‘Well, if they've got it, chances are we do, too,’” said David Wright, Extension agronomist at the North Florida Research and Education Center in Quincy, Fla.

The rust was found Nov. 15 by plant pathologists in a Group 5 research field on the Quincy station. Later, pathologists also searched kudzu — another host of the rust — near the infected soybeans. They did find rust on the invasive vine, although the infection was not as great as it was on the soybeans.

Wright said infected soybean plants were found on row ends that deer had been grazing. “There was some regrowth due to the grazing. It was on those green leaves that we found the lesions. It was very important to have that regrowth, actually. Without it, all that we'd have had to look at were dried leaves on the ground.”

In Alabama, a suspicious soybean sample from a field in Mobile County tested positive for the rust.

At the same time, a county Extension agent in extreme southwest Georgia found the disease in soybeans nearing harvest. It was only the first of many suspicious samples pulled in the state.

“Our diagnostician suspects, based on samples brought in, that we've got the rust in a wide swath across the coastal plain,” said Bob Kemerait, Georgia Extension plant pathologist. “It appears to be widespread. In fact, in most places it was looked for, it was found.”

The rust hasn't been confirmed on Georgia kudzu yet. However, a sample from Seminole County looks “very likely” to be infected.

The question Kemerait is asked: How is Asian soybean rust being found in so many different scenarios and areas in the state so late in the year?

“The first thing is we believe it came in on a hurricane. Second, numerous hurricanes and storms pounded us in a short time. That kept us out of the fields. Soybeans are a fairly minor crop for Georgia, and when growers were able to get back in fields, it was time to harvest peanuts and cotton. Third, soybean rust symptoms late in the year are almost exactly what growers expect to see in a healthy crop — drying and defoliation. Had it been earlier, we'd have been more concerned.”

Arkansas was added to the list Nov. 22 when a West Memphis-area soybean plant was confirmed to be hosting the disease. Since that initial confirmation, the disease has been found widely in the state.

“Most (infected) fields are along the eastern edge of the state. We've found suspect samples — not confirmed — as far north as Paragould (near the Missouri Bootheel) and as far south as Chicot County (bordering Louisiana),” said Rick Cartwright, Arkansas Extension plant pathologist.

The rust is being found on “old, late plants waiting for a frost to kill them,” said Cartwright. “Everyone needs to remember that after the first frost the rust will be over for Arkansas this year. It'll be killed back farther south.”

The unfortunate thing with the disease is no one “has any idea what it will really do” in the Mid-South, said Chris Tingle, Arkansas Extension soybean specialist. “We're basing our decisions on what's been seen in South America. It could turn out to be much worse than what they have there. Then again, it could be a very minor disease for us. We just don't know. This is the beginning of our information gathering.”

Tingle said his initial surprise at finding the rust so far north diminished after he considered shifting soybean systems in the state. “When we got the word on rust in Louisiana, I contacted agents in southeastern Arkansas. You know, ‘Let's get out and make sure we're clear.’

“They didn't find anything. But we've seen a tremendous push in that area towards an early-planted system. So the crop in the southeast was mostly out of the field by mid-September. That meant there were fewer chances to find (rust) there. On the flip side, as we move north, there are more opportunities for the disease to be expressed late. It isn't so shocking, therefore, that the rust was found farther north first.”

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