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Waging war on microscopic pests

Although it is admittedly an unusual claim to fame, Ken Middleton has become accustomed to being known as the farmer researchers can count on for field test plots brimming with record high nematode populations.

Middleton, who farms cotton near Glen Alan, Miss., battled reniform nematodes for a decade before joining forces with researchers at Mississippi State University to try to control the microscopic pests.

According to Gary Lawrence, a nematologist at Mississippi State University in Starkville, Miss., reniform nematodes have been documented in 51 counties in Mississippi, with a total of at least 414,720 acres infested with the pest.

“In one of our fields this year, researchers found more than 60,000 nematodes in just one pint of soil. I believe that’s a new record,” says Middleton. “The only farmers in my area without nematodes, though, are the ones that aren’t testing for nematodes.”

Lawrence says cotton growers are often unaware of the reniform nematode populations present in their fields because nematodes are nearly impossible to scout for, and it is often difficult to see any symptoms of injury caused by the pest.

“Often cotton yields go down over a number of years and you’ve tried everything you can think of but you can’t seem to boost them back up. In these cases, if you take a nematode sample from the soil you’ll usually find a high population of reniform nematodes that are to blame for the yield decrease,” Lawrence says.

Five years ago, Middleton began a collaborative study with Mississippi State University testing the use of fumigant soil treatments to control the nematodes making their home in his cotton crop. Researchers are also testing alternative control methods on the Washington County cotton farm, but Middleton says the “most troublesome” method of a fumigant application still seems to work the best.

Middleton injects 1.6 gallons per acre of the liquid fumigant, Telone II, into his cotton ground three weeks to a month before planting. Using a modified eight-row ripper hipper, he knives the fumigant down 15-inches into the soil using nitrogen-powered pressure while bedding his rows. His estimated cost for the treatment is $18 per acre.

Another control treatment that Middleton says shows promise is an application of Vapam. He is currently testing the fumigant product at set rates of 3-, 5- or 8 gallons per acre and at adjusting rates in that range made with a variable rate applicator. Application costs for Vapam, he says, are running between $15 for the low rate of 3 gallons per acre to $40 for the highest rate. “The variable rate, if it works, can save you a pile of money as expensive as these products are,” Middleton says.

“We’ve seen tremendous yield increases with the Telone II treatment, even at a reduced rate of 1.5 gallons per acre,” says Lawrence. “We’re also seeing nematode reductions with Vapam as compared to our Temik control treatment method.”

Other control methods being tested on Middleton’s farm include: Temik, Vydate C-LV at 4 ounces per acre followed by Temik at 3.5 pounds per acre, three consecutive applications of Messenger, and Messenger in combination with Temik.

One of the more recent projects researchers have initiated on Middleton’s farm is the study of the horizontal and vertical movement of reniform nematodes.

“This is the most important and relevant research I have ever seen. We’re finding over 2,000 nematodes per pint of soil as deep as 4 feet into the soil,” Middleton says. “We didn’t know until we began this study that we have a perpetual supply of nematodes 4 feet down in the soil. It shows us that we will never get rid of nematodes and the most we can hope for is adequate control.”

Early results from the study show that reniform nematodes apparently move deeper into the soil during, for example, a corn rotation, and then move back up in the soil depth to the plant roots when crops such as cotton are planted.

Lawrence has found that there is virtually no reproduction of reniform nematodes during a corn rotation, with the exception of any weed areas present in the field. However, despite this fact, the nematode populations down about 3 feet into the soil remain present in high numbers.

“If we sample at shallow depths it looks like we are doing a good job reducing populations, but deeper into the soil the nematodes may number about 20,000 per pint of soil,” he says. “We’ve found that reniform nematodes are very resistant and move more than we previously thought. They simply move deep into the soil during a corn rotation, waiting for that next cotton crop.”

While Middleton hasn’t rotated corn into his cotton fields for two years, he says that next year may be the year to add corn back to his crop mix, assuming the economics are right. “The best program, if you can afford it, is to rotate into corn for two years and then start a fumigant program to continue controlling the nematodes.”

Reducing nematode populations with a corn rotation and then not beginning a chemical control program, he says, “is like taking antibiotics and then as soon as you feel better, throwing the bottle away.”

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