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Mid-South: Wet conditions create crop concerns

Like many Louisianans, Clayton Hollier is watching Tropical Storm Gustav with a wary eye. Deep into the cropping season, his waterlogged state is already experiencing a stop-and-go harvest and “the last thing we need is more rain,” says the LSU AgCenter plant pathologist.

“Growers are trying to get crops cut as quickly as they can. Even if Gustav doesn’t hit Louisiana directly, it could still exacerbate current, or looming, problems.”

Among those problems are increasing disease concerns, including Asian soybean rust. Although the rust has yet to show up in soybeans, it has been found in south Louisiana in several kudzu patches.

“One was in Iberia Parish, on the coast, at a site that had rust for the past two seasons. We’d been surprised it hadn’t shown up there yet this year. But, finally, it has.”

The leaves were collected Aug. 21 and Aug. 22 by Hollier’s associate, who confirmed the disease on Aug. 25. On Wednesday, “she found some rust in kudzu in Baton Rouge along some railroad tracks. I sent out an alert: ‘No rust has been found on soybeans in Louisiana during the 2008 growing season. But with the rain events of the last month, observations of soybean rust on soybeans are likely. But there is no immediate need to make applications of fungicide for rust management.’

“There’s been no widespread finding of rust. However, the weather conditions over the last month — rains from Hurricane Fay, and afternoon showers regularly — have added to worries about rust picking up. We’ll keep farmers fully informed about any new threats that pop up.”

The story is much the same in Mississippi, where the disease has been found at several sites.

“Rust is in Florida, Georgia, south Alabama, Louisiana and Texas,” says Billy Moore, Mississippi Extension plant pathologist emeritus. “Based on current weather conditions, we’ll be seeing it pick up here in Mississippi. But by then, the bulk of our soybeans will be out of danger.”

In a recent scouting trip through south Mississippi, Moore and colleagues “walked through some Jackson County hot spots, four abreast. It just so happened, after we’d looked and looked, that Malcolm Broome (a retired researcher with Mississippi Extension) pulled a leaf and said, ‘Hey, this is rust.’

“But that was it. We searched all over and couldn’t find more. It was the luckiest thing. I’m sure there’s more rust than that there, but it’s very rare.”

The team then headed to Wilkinson County.

“There’s a kudzu patch there that was heavily infected with rust last year. Tom Allen (plant pathologist stationed at the Delta Branch Station in Stoneville, Miss.) found a few pustules on one leaf. And that was it.

“So, these latest finds are at extremely low levels of inoculum. We’re really not concerned about what’s coming out of Mississippi’s infected sites and we’ve not changed our recommendations: a fungicide is not warranted yet.”

However, Moore says Hurricane Fay brought in conditions that favor the rust.

“Temperatures have cooled and there’s plenty of moisture. I’m more concerned about what might be coming out of Florida, where rust has been reproducing rapidly over the past week, or so. Fay could easily have moved rust spores into the Southeast and Mid-South.

“But even with that situation, most of the soybeans in Mississippi are close to being out of vulnerable stages. That doesn’t include 500,000 acres of wheat-beans in the state, of course. If rust does hit, some of those beans could be hurt.”

The risk for rust moving into Arkansas’ soybean crop is “quite high,” says Scott Monfort, Arkansas Extension plant pathologist. “Of course, that’s based on current, and expected, weather conditions and those could change. Another thing to consider is the inoculum levels in neighboring states is low.”

What is “kind of scary” according to Monfort: Hurricane Fay moved across Florida — which has rust — and then traveled towards the Mid-South. “Extreme eastern Arkansas was touched by a couple of bands off Fay. Those could have brought (rust) spores. We’re keeping up with monitoring efforts and if anyone finds something suspicious, please let us know.”

Other issues are beginning to develop in the Arkansas soybean crop.

“Frogeye, cercospora leaf blight and aerial blight are hitting some areas. Interestingly, one of the biggest problems showing up in soybeans is nematodes. A lot of that is attributable to acres moving from cotton to soybeans. Lots of that former cotton ground has serious issues with rootknot nematodes and now those have shown up in soybeans.”

Hollier says Louisiana growers are also facing “a range of things. We have soybeans that were planted in late March, April and May. Those are maturing and, in some areas, farmers have been able to dodge rains and cut them.

“However, we also have a lot of full-season soybeans that were planted later — say in late May and June — along with double-cropped beans behind wheat. Those are the beans to be concerned about. We have beans from late vegetative stages all the way to full maturity.”

The frequent rains have also hurt other crops in the state. “Corn is showing typical stalk rot — wet rot issues with fusarium and whatnot, especially in pockets in the south. Further north, we’re finding a lot of charcoal rot. It was dry in some of those ridge soils for a long time and some of the corn was either dryland or irrigation was a little late. Once the infection process begins, adding irrigation water doesn’t really inhibit the charcoal rot infection process. It’ll continue to develop.”

Reports of sprouting in both corn and sorghum are also picking up. “I just talked to a northeast Louisiana consultant who said he was seeing that in his area.”

Currently, Moore says he’s more concerned about Mississippi’s soybean crop “in general than about rust. The soybeans have had a lot of moisture in the last few days and Gustav could bring even more.”

Monfort says if more rain arrives in Arkansas the corn crop will inevitably suffer. “There will definitely be some stalk rot and corn will begin lodging quickly, if it isn’t already. That’s to be expected where there’s been 8, 9, 10 inches of rain in the last few weeks.”


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