New rust find in northwest Louisiana

Asian soybean rust has been found in northwest Louisiana’s Natchitoches Parish. Discovered in a Group 4 production field on Aug. 11, the disease was confirmed on Aug. 14.

The field “was almost far enough along not to worry with rust,” says Boyd Padgett, LSU AgCenter plant pathologist. “I’ve heard nothing about more being found in surrounding areas. That doesn’t surprise me. It feels like it’s about 300 degrees, right now. And there’s been no rain.

“Honestly, I’m surprised with this hot, dry weather it’s even moving slowly. The conditions have been very prohibitive.”

In terms of potential impact of the find, David Lanclos says he “was much more nervous about the rust find in Alexandria three weeks ago. Nothing bad has come of that and ever since the soybean crop has advanced in growth. There’s just not much left for rust to jump on in the state.

“In the northwest region, drought is wearing the crop out, so this find is a minor worry,” says the LSU AgCenter soybean specialist. “Most of those beans are early and some are already coming out of the field.”

Soybean harvest in the state is going “full blast. We’re probably pulling 10,000 acres a day, right now.”

Lanclos, who walked the infected field, is “amazed” rust was found. “It’s so dry there are big cracks opened up. Regardless, he farmer has applied a triazole so the crop should be fine. The incidence was very low.”

Soybeans in the northeast are “at least R-5,” says Padgett. “Most are done or finishing out. Harvest is moving along. Yield reports are all over the board.”

There are “a few” beans still in susceptible stages.

“Those are mostly beans after wheat. Before treating any of those, producers need to consider yield potential. Anyone wanting up-to-date news on ASR should check the toll-free number (800) 516-0865.”

Arkansas reaction

“We don’t think (the Natchitoches find) is any cause for alarm,” says Trey Reaper, Arkansas Extension soybean verification coordinator. “It’s still 100 miles-plus from the state line. Even so, we’re continuing to scout intensely, especially in southern Arkansas.

“Remember, it was a good three weeks ago when it was found in Alexandria. In all that time, it only jumped a parish or two.”

If the Arkansas crop can escape the disease for another three weeks, “we’ll be out of the threat window. Many of our south Arkansas beans are already at R-4. They’re beginning to develop full seed and it won’t be long before they reach R-6.”

Judging from ASR’s progress in Louisiana this year, it doesn’t appear the disease “will blow up in our fields overnight. We’re not recommending growers spray for rust. If they want to treat with a fungicide for foliar diseases like frogeye or aerial blight, we recommend they stay with full-label products like Quadris or Headline. At this point, a rust material isn’t warranted for protection.”


The USDA recently forecast Arkansas to produce a 35-bushel state average.

“That’s optimistic,” says Reaper. “I don’t want to be pessimistic, but the crop is shorter and a 35-bushel average doesn’t seem plausible. The conditions the crop has been under all year — whether early-season or late-season fields — have meant a lot of stress from heat and/or drought.”

There are some highly productive fields that will cut 60 or 70 bushels.

“In general, though, we’re off from last year. It’s been very difficult to keep up with water demand. And as incredible as it sounds, it seems the heat — especially at night — is even worse than it was last year. That has taken a heavy toll on the crop.”

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