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Soybean rust spreads slowly across Mid-South

Wind and rains generated by a trio of recent hurricanes pushed Asian soybean rust deeper into the Mid-South. However, despite the list of soybean rust-hit counties seeming to grow by the day, most of the region’s soybeans are nearly out of danger.

“We’re almost out of the woods although the state does still have some soybeans between R-1 and R-5,” said Scott Monfort, Arkansas Extension plant pathologist, in late September. “We’re only worried about very small acreage.

“A week ago, we did put out a recommendation that growers have a good look at their soybeans and make an educated decision about whether to apply a fungicide. We did that because the rust was popping up everywhere.”

So far, the northernmost Arkansas county with confirmed rust is Woodruff.

“Most of the counties below I-40 have rust. I believe there are 12 counties total with the disease currently.”

Most of the infections have been at low levels, although the rust is beginning to increase in some fields. The situation is likely to get worse only in fields already infected.

“Right now, soybean rust won’t move very far — or from field to field — because of the warm, dry weather,” says Monfort. “We have clear skies and the rust spores won’t be able to remain viable and travel far.”

Reached in Mississippi’s Holmes County where he was scouting for rust, Billy Moore said around 25 counties in the state had the disease.

“Truth is, you can walk into the majority of fields in the Delta and find soybean rust,” said the Mississippi Extension plant pathologist emeritus. “Rust is all over the state but I’m not concerned about it too much. The beans are maturing and, with rare exception, it’s too late for it to do damage.

“This morning, we did find rust in some R-5.4 soybeans and suggested the farmer consider a fungicide. The fields had also sustained some stinkbug damage. Hopefully, he’ll knock out two problems with one stone.”

However, as far as soybeans needing a fungicide treatment for rust, that was an outlier. The area of the state that’s especially threatened by the disease “is from Vicksburg down to Fort Adams and Wilkinson County. There, they had early floods of the Mississippi River and planted extremely late.”

Even with the problems this cropping season, Mississippi has some of the “best wheat-beans I’ve ever seen. This fall has been unusual and some of the double-cropped beans got rainfall at just the right time. If things continue and wet weather doesn’t set in and cause rot, some of those beans will be outstanding.”

For Midwest growers, “there are still concerns with rust,” said Moore. “Growers in that area should be watching the Delta — hopefully, they’re treating us like their sentinel plot. That’s particularly true for farms around Iowa that planted so late after spring floods.”

Moore said a variety trial near Parchman, Miss., is of great interest. “For some reason, a tremendous amount of rust has shown up there. I don’t know I’ve ever seen as much rust anywhere. You can pick up a leaf — any leaf — and there are hundreds of pustules. I’d like to know why that one spot is so hot with rust.”

Back in Arkansas, Monfort said not many fungicide applications have occurred “for soybean rust alone. Applications that have taken place — and I’m talking about a tiny percentage of our soybean acres being sprayed — are typically targeting other diseases, as well.”

How did the rust arrive? “It was probably a combination of hurricanes Fay and Gustav. I don’t think Ike had much to do with it. Low-level inoculum appears to have come in with the first two. It took about two weeks to build up enough for us to find rust.”

Other diseases are also popping up. “A little bit of frogeye is showing up along with aerial blight. We’re seeing some late-season anthracnose, some stem blight and little bit of charcoal rot.”

Even so, when comparing all the crops after the trio of powerful weather systems, “soybeans appear to be faring best. A lot of our rice and corn has been laid on the ground. Some soybeans have lodged, but not like the other crops. If we can get some good, dry weather from here on, maybe the soybean-growing season can end on a positive note. I know that’s what we’re all hoping for.”


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