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New cases of Asian soybean rust popping up

Now that southern soybean farmers are putting the finishing touches on the 2005 crop, Asian soybean rust has begun showing up in fields from Louisiana to North Carolina, prompting experts to ponder whether this is part of a pattern with ASR in the United States.

As southeast soybean crops dry down, Asian soybean rust is becoming easier to find, leading to new reports of the fungal disease popping up all over the Southeast. In late October, 10 new cases were announced in Alabama, some 30 cases had been located in South Carolina and, for the first time, a handful of cases were found in North Carolina. Georgia also continues to find new incidences of the fungal disease regularly.

Asian soybean rust has also moved further west. On Oct. 28, Ray Schneider found the first incidence of the disease in Louisiana this year. Schneider, a professor of plant pathology with the LSU AgCenter in Baton Rouge, has a good eye for the disease. On Nov. 6, 2004, he was the first to find Asian soybean rust in the United States. “We’ve had sentinel plots out since March and have checked them at least weekly,” said Clayton Hollier, Louisiana Extension plant pathologist. “We’re at 98 percent harvested so this isn’t a concern for our crop. But we’ll continue to monitor things because people further north of us haven’t harvested yet. They need to know if this rust is moving and is a threat to them.”

In Alabama, Ed Sikora, the state’s Extension plant pathologist, has been checking many kudzu patches for the disease. “(On Oct. 23), I was heading home from a meeting in Tallahassee. Going home, I drove up the eastern edge of Alabama and stopped to check 14 random kudzu patches along the road. Of the 10 new incidences I found, seven were on kudzu. The infection rate, except for one case, was low.”

Most Alabama farmers are happy with their soybean yields. “Harvest is nearly done. I’ve heard some excellent yields. Depending on the area, farmers report 50-, 60- or 70-bushel yields. As far as I can tell, there hasn’t been any significant soybean rust damage to a commercial field. I’ve traveled back to fields where rust showed up at mid-season. The crops still looked good. The impact of soybean rust has been negligible in Alabama - at least from what I’ve been able to document.”

With foliage dropping, soybean rust is getting easier to find. Any remaining green leaves get attention.

“Sometimes there are still some beans at the field edges that have green foliage,” said Sikora. “The three fields I found rust in on Saturday were all that way – rust on a few green leaves.”

In Georgia, soybean harvest is nearing full swing. “There are some good beans and some sorry ones,” said Phil Jost, Georgia Extension soybean specialist. “The August/September drought we experienced really hurt. The good beans are cutting 40 to 45 bushels. The bad beans won’t do much better than 20 bushels.”

USDA has the state average pegged at 30 bushels, down from earlier this summer.

Towards the end of the season, soybean rust has become widespread in Georgia. It’s yet to be determined if the disease has had any yield consequences.

“Our gut feeling is there are very few, if any, fields with enough rust infestation to hurt yields,” said Jost. “Some of our untreated trials, especially in the southwest corner of the state, will probably see yield drop. But as far as commercial fields, we don’t think there’s much damage. It’s safe to say it’s more widespread now than it was a year ago when the hurricane brought the rust in. But it hasn’t hurt much.”

Jost suspects a “large majority” of farmers likely sprayed a fungicide at least once. “No doubt that has something to do with low infection rates.”

Georgia Extension agents have aided in finding the new cases of rust.

“Right now, the disease is easy to find. So agents are out pulling a couple of leaves and sending them in. We want to know how far north the rust has traveled. It’s almost to the Georgia/Tennessee line. Most of the new finds are a pustule here and there, nothing major.”

Still, the new finds are interesting and disturbing due to the dry conditions Georgia has experienced since mid-August.

“It’s been extremely dry,” said Jost. “Yet, the rust has moved and progressed. That worries me.”

Both Jost and Sikora are also concerned about what an increased rust spore load will mean for crops next year. Soybean producers have yet to see what the disease is truly capable of.

“The fact it has grown to the level it has this year is, in my opinion, just an indication we’ve increased the innoculum source,” said Jost. “That means there will be a greater potential for trouble with soybean rust next year. If we have early-season wet conditions, this disease could be much, much worse than we’ve seen.

“Of course, it’s all weather dependent. If 2006 is dry, rust may not be an issue. But if we find rust early in the season, knowing what it can do to our crop, we’ll recommend fungicides again.”

Does Sikora see any reason to tweak fungicide recommendations?

“At this point, they’re solid. And they’d better be. I believe innoculum will continue to build in south Florida. I’m not trying to alarm anyone but that’s my fear. “What I don’t want to have happen is producers look only at this year and not take soybean rust seriously. This isn’t just a one-year problem. We must remain vigilant.”

Due to high input costs, expectations in many states are for a larger soybean crop next year. While harvest may be keeping such talk to a minimum, Jost hasn’t heard much along those lines.

“With input costs being so expensive, we’ll probably see some increase. But I’m not hearing a huge shift. If a shift occurs, though, there’s no doubt the extra acres will play a part in how this disease moves across the state.”


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