Arkansas' Prairie County has a history with nematodes, so it didn't surprise Chris Tingle that first reports of the pest came from there.
“But now we've got them in Lonoke and Woodruff counties as well,” says the Arkansas Extension soybean specialist. “Those are counties where we've definitely confirmed cyst problems. This week, I feel we'll get a bunch more calls. Right now, I'm in Cross County and it's hot and dry. Hot and dry conditions are what cyst nematodes normally use to turn symptoms on.”
So far, other than in the three aforementioned counties, the calls have been limited. But driving through the state, Tingle says he sees plenty of fields with “hot spots and defoliation that look like nematodes could be doing damage.”
The symptoms arise from a plant being drought-stressed due to a poor root system, says Tingle. Because of the abundant rains experienced earlier this season, many soybeans fields already have shallow root systems. The roots didn't have to explore deep into the soil to get moisture — it was easily available at the surface. That led to ill-defined root systems, and cyst nematodes are jumping on and making the problem even more acute.
By far, the Prairie County nematodes have been the worst, says Tingle. The damage in the other counties took longer to confirm and find.
“There aren't quite the populations on roots we've looked at in Lonoke and Woodruff counties. A lot of that is based on the cultural history of the individual fields.”
How bad a field is affected by nematodes has a lot to do with crop rotation.
“We see that in our verification fields where we've taken nematode samples over a period of years. Where rotation practices were employed, gradual nematode populations have declined annually. The decline isn't at a rapid rate, though, which is a bit disheartening.”
“Because crop rotation has been one of the cornerstones we've pointed to for dealing with nematodes. Of course, even a gradual decline is better than leaving a field in soybeans for years on end while nematode numbers grow uninterrupted.”
But that doesn't change the facts, says Tingle.
“If we're in a one-to-one rotation with rice, populations won't be affected much. You have to rotate to a non-host crop like grain sorghum. Or, in the case of cyst nematodes, corn can be brought in.”
In dealing with cyst nematodes, variety selection is the key recommendation the Extension Service can make. But before a variety can be recommended, the nematode race must be known. Fields must be sampled and race analysis conducted.
“Too often, the races we're picking up now have no variety defense. Regardless, you must know the races in a given field. Any farmer who thinks he's got a problem needs to grab a soil sample and some plant roots and send them in. The cost is minimal compared to the losses we'll see in some Arkansas soybean fields,” he says.
Race analysis takes a while — typically four to six weeks — and utilizes a process of elimination. It's an old method that's sound and true, but takes time. Another quicker method using genetic markers is being developed but is still in the preliminary stages.
Trying to stay up with the problem, Tingle has compiled nematode information for agents and producers. The data can be found in Extension offices and also in the soybean section of the www.uaex.edu Web site.
“The document explains symptoms, the proper way to sample, the proper way to check roots, and other nematode details,” says Tingle. “To tell you the truth, there's little new — no new recommendations — but it's in a reader-friendly format and should help producers. And there are plenty of pictures illustrate it.”