Cotton farmers and the agencies and industries that support them have three to four years to come up with new products, techniques or a combination of currently available strategies to manage nematodes before they lose Temik, a mainstay for crop protection for some 40 years.

Resistant cultivars may be the best option but currently less than a handful of varieties with only moderate resistance are available and putting resistance into a variety with the yield and quality traits growers demand will not be easy.

In the meantime, those varieties moderately resistant to root knot nematodes may be a better option than some believe.

“They may be more beneficial than some folks have given them credit for,” said USDA-ARS nematologist Richard Davis, Tifton, Ga., during a panel discussion at the recent Beltwide Cotton Conferences in Atlanta.

 “Moderately resistant varieties will not be the sole solution to replacing Temik,” he said, “but may be part of a program.”

The advantage can be significant, said Terry Wheeler, Texas AgriLife research pathologist at Lubbock.

“Partial resistant cultivars have enormous advantages,” she said, “and may add as much as a 500-pound-per-acre yield advantage in heavily infested fields.”

Wheeler and other panelists cited ST 5458, Phy 376, ST 4288 and DPL 174 as moderately resistant to the Southern root knot nematode.

“Resistance has several advantages,” Davis said. “It’s not an additional expense and has no effects on the environment. Resistance offers season-long control and is more consistent than other treatment methods. Plant resistance also limits nematode reproduction.”

A highly resistant cultivar is defined as one that reduces nematode reproduction below 10 percent in susceptible stands. Moderately resistant cultivars lower reproduction but not below 10 percent.

Davis said a resistant variety, Auburn 623, was released to breeders in 1970. “But we still do not have highly resistant cultivars. We’ve made progress but resistance is a multi-gene trait; that’s why it’s hard to breed nematode resistance.”

Several possibilities are in development, including Acala NemX, which Davis said is “unproven if it has different resistance genes from Auburn 623.”  

LONREN-1 and LONREN-2, two reniform resistant breeding lines, were released by USDA in 2007. “It takes time to get resistance into lines with acceptable yield and quality traits,” Davis said. “But we know the tools are there. Within two years we will have other resistant genes.”

Resistance will not be the end-all for nematode management, however. “We do see limitations for resistance,” Davis said. “Resistance is species specific and other nematodes might emerge as problems. Also, as we move away from nematicides we may encourage other nematodes to emerge.”

He said moderate resistance and a combination of chemistry and other practices may help limit population spikes. Cultural controls also may play a role.

He said continuous selection pressure could cause nematodes to break resistance.