Root-knot or reniform — either nematode species will play havoc with cotton yields, but options for control may make the former a bit more manageable.

Cotton farmers have available some varietal tolerance for root-knot nematode, says Texas Research Plant Pathologist Terry Wheeler at the Lubbock Research and Extension Center.

“Stoneville 5599 BR has tolerance to root-knot nematode,” Wheeler said at the recent Concho Valley Cotton Conference at San Angelo, “but we have no variety tolerance for reniform nematode.”

Chemical treatments have not been particularly effective either, based on Wheeler’s recent research.

“Last year (2006) was a disappointing year for pesticide performance on root-knot nematodes,” she says. “We saw no average yield increase across all 5 test sites with Temik 15G. Two sites gave some yield increase, but the overall test response in 2006 was not good.”

She believes it was due to the unusually hot, dry spring which made it difficult to get the chemicals into solution in the top four inches of soil.

“At our reniform test site, we got no yield increase at all from Temik 15G or nematicide seed treatments.” Typically she expects a 10 percent yield increase when the material is applied at planting.

Reniform nematode is expanding in the Southwest. Wheeler says a Lubbock research field has had a population for several years.

“On our irrigated land with reniform nematode infestations, yields dropped initially to 800 pounds, then 600, and now they are at 200 pounds per acre, even with Temik 15G applied.”

Materials in Wheeler’s tests include Temik 15G, Avicta Complete Pak, Aeris, Telone II, and Vydate CLV. She says Vydate CLV typically provides a “very good response in severe root-knot nematode infestations. With lighter infestations we see less response.”

She applies the material over the top, at the fifth-leaf stage, in two applications (8.5 ounces per acre for each application,17 ounces total) two weeks apart.

Wheeler advises cotton farmers contemplating adding subsurface drip irrigation to their farms to test for reniform nematodes first.

“Don’t install drip in reniform-infested fields, especially if the drip tape is laid in every other furrow,” she says.

Tests show nematodes will congregate in the bed and drip tape areas, with highest concentrations fairly deep, from one to two feet down.

She says fumigant treatments with Telone EC, applied at a depth of 1 foot through drip on 80-inch centers, was not successful, though knifing Telone II into the bed at a depth of 20 inches has been successful.

“We just can’t move the fumigant from the drip tape all the way over to the dry furrow.”

Rotation offers the best control option for reniform nematodes. When extremely high reniform numbers are present, Wheeler recommends a grain crop for two years and then cotton.

“After the numbers drop, then one year in cotton and one in a grain crop should reduce losses to manageable levels —but the rotation should be maintained forever,” she says. “Wheat is a good rotation, but make sure to control weeds during the summer because some weeds can host reniform nematodes. Fallow and dry is not a good option because, in the absence of a host, they survive better in dry soil than in wet soil.”

Research on variety tolerance for root-knot nematode has shown a good response with Stoneville 5599 BR.

“Water stress at flowering may be a factor,” she says. “Some years, in our test site, we could only provide 30 percent of the water demands at flowering.”

She says Stoneville 5599 BR has proven to be “less sensitive to water stress during flowering compared to the susceptible varieties in the test (FiberMax 989 BR and Paymaster 2280 BG/RR). Cotton infested with root-knot nematodes because of the galled roots is less effective at pulling water out of the soil.”

Wheeler says Stoneville 5599BR, compared to a FiberMax variety, was best “during drought conditions, meaning the differences between its yield and the more susceptible varieties were largest under dry conditions. Situations with better water during flowering “favored FM 989 BR, partly because of better productivity, but also due to better loan value.”

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