Two species of nematodes — the reniform and the root-knot — cost Alabama producers about $37 million annually, says Bill Gazaway, Auburn University Extension plant pathologist.
“Most of the damage — about 92 percent of it — comes from the reniform nematodes,” says Gazaway. “But in regions of the state, such as east Alabama, we've also got to be concerned with the root-knot nematode.”
The root-knot nematode, he adds, is found mostly in sandier soils. “Normally, whenever you have cotton root-knot, you'll also have fusarium wilt. For controlling root-knot nematodes, we recommend rotating with peanuts. Do not rotate with corn. It's very susceptible. Many years ago, we'd recommend corn as a rotation, but we've discovered that it's very susceptible,” says Gazaway.
No currently available corn hybrids are resistant to root-knot nematodes, he says. “Talk to your plant breeders about developing a package that's resistant to root-knot — it's very much needed,” he says.
For cotton fields with heavy root-knot pressure, Gazaway recommends the use of a nematicide with a cotton variety that is resistant or tolerant to the root-knot/fusarium wilt complex.
“We look at about 15 commercial varieties each year in Alabama, and we screen for resistance to fusarium wilt. We usually find those varieties that are tolerant to wilt also have fairly good root-knot resistance. You might want to look at varieties like Fibermax 991, Stoneville 5599, DPL 491 and DPL 555. There also are others, and they all have fairly good resistance,” he says.
Rotating with peanuts is an excellent choice too for helping to control root-knot nematodes, says Gazaway, especially two years of peanuts followed by one year of cotton.
“Peanuts also are a good rotation crop for reniform nematodes. But do not rotate with corn for root-knot nematodes. You might as well be growing continuous cotton for the good corn will do you in a rotation,” he says.
Several years of research have proven the value of rotation for controlling reniform nematodes in cotton, he says. “We get a tremendous boost whenever we grow peanuts. And corn actually is a good rotation crop for reniform nematodes. But if you have a mixed population in your fields of both reniform and root-knot nematodes, don't stay too long with corn because it'll flare the root-knot problem. In north Alabama, we've caused some root-knot problems by growing two continuous years of corn,” he says.
In south Alabama, producers need to be aware that they can cause problems other than nematodes if they grow more than one year of continuous peanuts, notes Gazaway. “We're down to corn and peanuts as far as rotation possibilities for controlling the reniform nematode,” he says.
Gazaway recommends that cotton producers use a nematicide in fields that have shown a history or a problem with nematodes.