Asian soybean rust identified in southeast Mississippi field

Asian soybean rust has been discovered in a southeast Mississippi soybean field in Jackson County.

Malcolm Broome, a member of Mississippi's ASR team, found rust just north of Moss Point on Sept. 6, said Billy Moore, Mississippi Extension plant pathologist. “It's in a nice-size soybean field that we've been watching for a long time. We thought ASR might show up there because of its proximity to some positive finds in Alabama. They've found ASR in the Foley area of Alabama — that's probably less than 60 miles away.”

In the infected field, beans at bloom and pod-set were chest-high and had adequate rain. Under the canopy, “it was an incubator. That field, at 65 acres or so, is probably the largest that far south. It's not too far from the coast and ASR was found in a spot about as big as a car. The inoculum level was low.”

The field is a bit beyond R-6 and ASR won't hurt its yield. Most of the beans in the area are also mature enough that farmers will not worry about the find. Moore, however, is concerned about a few fields.

“There's a variety trial site down there that we're monitoring closely. Some of those beans are at R-1.

“There are also some extremely late-planted beans in Jefferson County near Collins, Miss. Most of those are in scattered, smaller fields. Farmers there had such incredibly dry weather that it led to late planting.”

Producers in the area with soybeans at R-5.5 or younger should consider a fungicide application, particularly a triazole or a tank mix. Soybean growers in north Mississippi and the Delta “have nothing to be concerned about at this time.”

Add a little moisture to cooler conditions Mississippi is currently experiencing “and ASR would have a perfect environment. But we're at least 65 percent harvested. There are very few beans ASR could jump on and damage.”

Still, the ASR team remains vigilant.

“We want to continue to learn what this rust will do in our environment. We need to gather as much data as possible. Those efforts will continue at least until first frost.

“We need to do that so we can develop predictive models. Those would help us with crop management and expectations. One of these days, we'll have a model that will predict when a producer should spray a fungicide. That's where this effort is ultimately leading.”

One thing already found is a tremendous difference in susceptibility between kudzu patches. That has become especially evident since ASR was found in southwest Mississippi earlier this summer.

“It's amazing. An infected site in the southwest has a big patch of kudzu right across the road. Down the road — maybe 100 yards away — there's another kudzu patch. Actually kudzu runs up and down the road in that entire region. In that whole area, we've found ASR in one patch. None of the rest has any and we've searched and searched.”

Tests conducted on kudzu seed collected from 50 sites around Mississippi bolster Moore's field observations.

“Genetic differences exist in our kudzu. That's lucky for us — not everything is just laying down for this rust. Based on what I've seen, we've probably got a lot more kudzu not susceptible to rust than we initially feared. I wish our soybeans had the same variability — all our beans are susceptible.”

Moore expects ASR will be a problem for the Mid-South crop only one or two years every decade.

“What happens next year — and don't forget there's rust in Mexico, now — largely depends on what happens in the overwintering sites. Will it be stable and stay at the same levels of last winter? If so, I don't anticipate much of a problem for us. But if the fungus is very active on alternative hosts in the overwintering sites, inoculum builds up, mean air currents are strong enough to bring it to Mississippi, and there are extended optimum conditions (including frequent rainfall), watch out. But that's a lot of hoops to jump through.”

Farmers need to remember that even though the crop is susceptible to rust at any stage, “it isn't until bloom and after that the susceptibility increases dramatically.”

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