No easy button for controlling nematodes in cotton

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You might say it’s more of an art than a science when it comes to controlling root-knot and reniform nematodes in Mid-South cotton fields.

More farmers are learning they need to soil sample to determine how much of an impact the underground pests may be having on their yield. But then they have to be able to relate those numbers to the treatment thresholds for the region’s soil types.

“You have to remember that taking a soil sample is one of the most important things you can do to determine what your nematode population is,” says Tom Allen, Extension plant pathologist with Mississippi State University. “You can’t tell just by looking at your field.”

Dr. Allen, a speaker at the annual National Conservation Systems Cotton and Rice Conference in Tunica, Miss., a displayed a slide showing the recommended treatment threshold levels for lance, reniform and root-knot nematodes on light, medium and heavy soils in the Mississippi Delta and other parts of the Mid-South.

“For nematodes we do have some pretty cut and dried numbers,” he said. “But I will tell you that a lot of these numbers were decided by a group of people sitting around a table. There is not a lot of scientific information that really suggests that either over or under that population number will cause any yield loss, and it is difficult to wrap your mind around what number you have to have.”

Allen also noted that the thresholds can vary considerably between the season of the year and the soil type, a fact which can cause issues since many times all three soil types can be found in a single field in the Delta region.

“In certain areas, you will have pockets of high numbers. So from a site-specific management purpose, that’s important.”

The situation is also complicated by the fact that Temik or aldicarb, one of the leading nematode products for decades, is no longer available despite the efforts of some would-be manufacturers to bring it back on the market.

Growers are left with seed treatments; side-dressing of Vydate; applications of soil fumigants like K-pam or Vapam or Telone II, a by-product from the automotive industry; non-host crop rotation or planting resistant varieties to try to address their nematode problems.

Telone II has proven to be highly effective in controlling all types of nematodes, especially when used in combination with other control measures. It is expensive in that it costs $15-$16 per gallon and requires an application rate of three gallons per acre to be effective. Some problems with supply have also occurred.

Allen and other Mississippi State researchers have been working with producers like Kenneth Hood of Gunnison, Miss., to develop systems for delivering Telone II precisely where it is needed to have the greatest impact on nematodes.

Some of the results of the research have been mixed, but, in areas where the scientists, have matched the Telone applications with high populations of root-knot nematodes, they have observed yield increases of more than 150 pounds of cotton lint per acre.

“The major reason we use that product (Telone II) and do a pretty good job of using it is we have to use it from a site-specific management practice,” he noted. “So you’re only applying it in a small part of a field because when you’re talking about $16 a gallon at a three-gallon-per-acre rate you’re talking about $50 an acre for one input.

“It is fairly easy from an application standpoint, and it does a spectacular job of controlling nematodes if you combine additional management practices with Telone.” 

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