A multi-year research project has shown that a proper rotation will work just as well as a nematicide in keeping reniform nematode populations at manageable levels in Alabama cotton fields.
"We probably have the longest on-going rotation study of this type in the United States," says Bill Gazaway, retired plant pathologist and nematologist with the Alabama Cooperative Extension System. "We began the study in 1994, and we’re continuing it through this year in Huxford, located in southwest Alabama."
The initial study, he explains, was a four-year project — looking at one, two and three-year crop rotations with continuous cotton, and cotton treated with a nematicide and rotated with grain sorghum, corn, resistant soybeans and bahiagrass.
"Although reniform nematode populations were lowest at the end of the three-year rotation, we found that with non-host crops such as corn, grain sorghum and reniform-resistant soybeans, we could lower populations to a sufficient level to where we felt it would be practical to go back in with cotton after one year," says Gazaway.
In the second phase of the study, Gazaway took bahiagrass out of the rotation and added peanuts. "We also wanted to look at the effect of different cover crops on reniform populations. I selected vetch because it has shown susceptibility to reniform nematodes in greenhouse studies. I also looked at ryegrass and leaving the field fallow," he says.
The study has shown, he says, that the choice of a cover crop doesn’t affect reniform populations. "Vetch did not adversely affect yield nor did it greatly affect nematode populations over the winter. Since the test is located so far south, we probably can say this would be a safe bet anywhere in Alabama. If it doesn’t impact nematode populations in the southern part of the state, it certainly won’t in the north."
Gazaway concludes from the research that Alabama cotton producers can do a good job of controlling reniform nematodes by rotating one year with corn, peanuts, grain sorghum, grass crops such as bahiagrass or certain reniform-resistant soybean varieties. Many weeds — particularly broadleaf weeds — are good hosts and will increase reniform populations, he adds. Therefore, it is important to control weeds when growing non-host summer crops.
"This doesn’t mean we can do it in other states," says Gazaway. "We desperately need rotation studies throughout the South to see which crops will work and to see how nematode populations respond in other soils and at different temperatures."
Since the reniform nematode produces extremely large populations within a single growing season, remedial measures such as crop rotation or nematicides are effective for only one cotton growing season, he says. Crop rotation or a nematicide must be used the following spring where cotton has been grown the previous season.
The movement of peanut acreage to southwest Alabama makes peanuts a good rotation choice for managing reniform nematodes, says Gazaway. And, while peanuts also are a good rotation for root-knot nematodes, the same can’t be said for corn.
"Corn is a good rotation only for the reniform. It’s a dangerous crop to grow if you have root-knot nematodes. Previous studies have shown that corn can increase root-knot populations."
Nematicides do an excellent job of managing reniform nematode populations if the materials are applied properly and under the right conditions, says Gazaway.
"We’ve looked at various means of incorporating nematicides. In the case of Temik, we looked at broad-band applications or a T-band, where we put a little Temik in the seed furrow for thrips control and the rest in a 6-inch band lightly incorporated on the surface for nematode control. Although broad-band applications provided excellent reniform control, they were not safe because we could not incorporate Temik in the soil properly. We found that putting Temik in the seed furrow at planting was safer, provided good nematode control, and was easier for farmers to apply.
"Excessive rainfall at the time of application can be just as bad because Temik is a water-soluble compound, and it can be washed out of the root zone during heavy rains."
Gazaway also has tried in-furrow treatments with adequate results. "We’ve also looked at sidedress applications, and we’ve seen good results and bad results. We’ll continue looking at that this year."
The fumigant Telone works ideally under good conditions, he adds. "Because Telone is a fumigant, it must be put out a week or two ahead of time to avoid hurting the plants. In the past, we’ve had the best success with Telone by injecting into a well-prepared seedbed, free of clods and undecomposed plant material."
Telone works best, he says, in warm, dry conditions, with the soil temperature above 50 or 60 degrees. "We’ve looked at Telone as a spring and fall application in Huxford, and we’ve found that fall is as good as spring for applying Telone in that part of the state. In north Alabama’s Tennessee Valley, conditions often are wet and cold in the spring, so we’re trying to convince farmers in that region to apply Telone in the fall, after the crop is out of the field."
Gazaway also is looking at applying Telone with a Yetter rig for minimum or strip-tillage situations. "This will be a real breakthrough if we can make it work, considering the large amount of minimum tillage acres in north Alabama."
The fumigant Vapam also has done a good job controlling reniform nematodes in the Huxford, Ala., experiment, he says. Various seed treatments did not look good in Gazaway’s research.