The 2002 crop marks the 50th year the National Cotton Council will track yield losses due to nematodes. The long-standing effort has raised grower awareness and reduced the negative economic impact of nematodes. However, nematodes remain a significant problem, and researchers see room for improvement in managing it.
The Council's Nematode Education Committee includes nematologists across the Cotton Belt. The workgroup meets once a year to report research efforts and update strategies and recommendations to better manage infestations in cotton. Don Blasingame, a plant pathologist from Starkville, Miss., leads the group.
“After so many years of studying this pest you would almost think at this point that we would know everything there is to know about it,” says Blasingame. “It's simply not true. Even though we have a tremendous database of knowledge about nematodes from years of studying the problem, we're constantly learning something new.
“Every year, that knowledge enables us to refine our strategies for dealing with this pest and helps us update management recommendations to minimize losses.”
Beltwide nematode losses for 2000 were estimated at 4.3 percent — $307.7 million. That includes $157.8 million for rootknot nematode, $129.1 million for reniform nematode and $20.8 million for all other species.
Reniform nematode, in particular, is continuing to spread and is causing considerable concern. Reniform nematode is often difficult to detect without soil sampling and is potentially more devastating than other species.
Charles Overstreet, nematologist with the LSU AgCenter, reports that reniform nematode is indeed becoming a bigger problem in Louisiana. “Most cotton-growing areas already have at least some level of reniform infestation,” he says. “We're continuing to find it at more locations and at higher levels.”
In Tennessee, Melvin Newman, professor of entomology and plant pathology, with the University of Tennessee at Jackson, also confirms that reniform is spreading in that state. “We first detected reniform nematode in Tennessee in 1992,” he says. “Of course, that doesn't mean it wasn't there previously, but there's no doubt it is spreading. Last year, we found it in about 100 fields in Crockett, Madison and Dyer counties. We're conducting much more intensive sampling now to try to pinpoint where the infestations are, and we'll continue that effort this season.”
Extensive nematode sampling in Mississippi has been conducted for years where the pest has been a common problem. Last year, a targeted sampling program conducted by Blasingame in three Mississippi counties showed that reniform nematode is being found in an increasing percentage of cotton acres.
“We took samples from random fields in Sharkey, Leflore and Coahoma counties,” Blasingame says. “Compared to data from 1986, we found that reniform nematode had increased 15 percent in Coahoma and 11 percent in Leflore. We didn't have 1986 data from Sharkey county, but our survey results from last year showed that 89 percent of the cotton acreage in that county is infested with reniform nematode. That's significant.”
In Arkansas, Terry Kirkpatrick, plant pathologist with the University of Arkansas, reports that both reniform and root-knot nematode continue to be the cause of considerable economic concern throughout the state. “Reniform nematode continues to be very widespread, and it's quite severe in several southeastern counties,” he says. “We've detected it in 10 Arkansas counties, and it's particularly problematic in Jefferson and Monroe counties.”
Only the Bootheel of Missouri seems to have escaped serious problems thus far. Al Wrather, plant pathologist with the University of Missouri's Delta Center, reports that reniform nematodes have been detected in a few fields in the state, but populations were low and did not cause yield loss. “That doesn't mean we're not going to get damage some day,” he says.
Growers are urged to sample for nematodes, particularly if yields have declined for no readily apparent reason. If nematodes are detected and exceed treatment thresholds, researchers recommend treating with the insecticides Temik or Vydate or a fumigant such as Telone.
Gary Lawrence, associate professor with Mississippi State University's Department of Entomology and Plant Pathology, says that his nematode research trials have shown the best results from an at-plant application of 3.5 pounds per acre of Temik plus two 8-ounce applications of Vydate. If growers opt for a split application of Temik, he says the best results have been 5 pounds of Temik at plant followed by 5 pounds at sidedress.
“These are our best control options in Mississippi,” he says. “Last year, the addition of Temik gave us about an 8 percent to 11 percent increase in yields. One of the benefits of using Temik at planting is the additional insect control that you get. We also generally see cotton start fruiting at a lower node where Temik has been applied at planting.”
In the presence of nematodes, a treatment almost always increases yields, according to researchers. “The growers in Tennessee that have gone to Temik are getting better yields now,” Newman says. “I think there had been a certain level of nematode infestation that had slowly built up in a lot of areas that was largely responsible for the general decline in yields. Now, that more growers are adding a nematode treatment, we're seeing yield increases.”
In Arkansas, Kirkpatrick says, growers use either Telone II or Temik to manage nematodes. “In extreme Southeast Arkansas, growers routinely apply Telone II at 3 gallons per acre at preplant for nematode control,” he says. “In the rest of the state, and particularly where reniform nematodes are prevalent, growers routinely apply Temik at 5 pounds per acre at planting followed by a sidedress application at 5 pounds at or just slightly before pinhead square.”
Grower awareness of the problem has certainly increased due to the efforts of the Nematode Education Committee. Each year, Aventis CropScience supports the efforts of the Committee through a grant to the National Cotton Council. The results continue to benefit growers across the Cotton Belt. In addition to research on treatment options, nematologists are now looking at various factors that impact how nematodes infest fields and what can be done to alter that pattern.
“There's some very interesting research being conducted about how nematodes move within the soil profile,” Blasingame says. “For instance, Gary Lawrence is working with a remote sensing project to see how easily nematodes are spread by such things as equipment and water. By developing a better understanding of where nematodes are and how they move around, we hope to ultimately be able to manage infestations more effectively.”