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Nematodes slash Arkansas soybeans

The first calls from concerned farmers came in mid-May. It wasn't long after that Lannie Ashlock realized how bad nematode pressure would be in Arkansas soybeans.

“There's a lot of this showing up in our rice/soybean rotation. That rotation is great for both crops, but it doesn't help us keep nematode populations down,” says Ashlock, the Arkansas Extension soybean specialist. “It seems like we're seeing a whole bunch of it on the western side of Crowley's Ridge. If we're not very careful, nematode troubles will explode.”

A contributor to this is that many of the high-yielding varieties — whether Roundup or conventional — have gone to the same genetic source of nematode resistance. That means varieties' resistance is typically targeted to only a select number of nematode races.

“You might change variety companies, but the resistance genes are coming out of the same parent. Over time, even though we originally had good nematode resistance, we've allowed certain races of nematodes to grow to devastating levels.”

In response to the problems, Ashlock is putting together an Aug. 30 tour of affected fields. “We want breeders to know the level of our distress. Hopefully they're already aware of it and have varieties in the pipeline to address this.”

There is hope. Ashlock says there is a public variety — Hartwig — that's resistant to all known races of cyst. Hartwig isn't a high-yielding variety, but if you've got a bad cyst problem, it could be a your best choice, Ashlock says.

“I hope breeders have already captured Hartwig resistance and are getting it into their varieties. These nematodes aren't just going to go away. They'll definitely be back next year. Farmers are wondering how close we are to getting some genetic help.”

Cliff Coker, Extension plant pathologist, agrees with Ashlock's assessment. “Cyst nematode is definitely the big story in soybeans this year. It's working some fields over. Actually, it's removing some fields from production,” says Coker.

Currently, Coker is involved in a program asking county agents to provide 20 samples from 20 fields in each county growing soybeans. The program is running soybean cyst race analysis free of charge through the end of the month. Normally, it costs between $10 and $15 to run a sample.

“We're asking agents to pull samples a little differently. They need to pull root samples with a little soil attached to the roots. This isn't a program to determine if cyst nematodes are in a field. We need samples of plants obviously affected by nematodes. This is a program to help determine what type of nematodes are in a given field.

“There are a lot of fields across the state — we're guessing 1.5 million acres — having problems with soybean cyst nematode. This problem isn't going to be short-lived.”

Many of the varieties planted in the state have a background that's resistant to Race 3, 6, 9, or 14. Coker says those four races probably aren't what's causing trouble.

“We're fearful it's Race 4 that's everywhere. That hasn't been determined, but we're suspicious. Hopefully we'll know for sure by the tour date.”

Things can get blown out of proportion, and Ashlock wants it known that this isn't a statewide epidemic. But there are areas that are affected terribly.

“Farmers are going to take huge hits. Some farmers will take a 25-bushel loss on irrigated land. That means they'll lose $100 per acre.”

And this isn't over. Ashlock says the state may soon see a lot of Sudden Death Syndrome. “Other diseases may manifest themselves due to the injured root system. And one thing is for sure: the soybean root systems are hurting. It'll take a couple more weeks to know if something else will pop up.”

Coker says he's already seeing SDS across the state. “This is happening on 45- to 60-bushel soybean ground. Some fields affected by this also have cyst nematodes. There's also some stem canker scattered about. But for the most part, disease pressure has been light.”

One way to deal with nematodes next year? More milo. “I think we need milo for a lot of reasons. Reducing nematodes means more will be in the state next year. It's not the most attractive crop for several reasons, but some farmers won't have much choice,” says Ashlock.

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