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.

Gene mapping and sequencing

In the future, Davis expects to see refinements in nematode resistance breeding techniques with improved gene mapping and gene sequencing. “We will develop more and better genetic markers and new sources of resistance, especially to root knot nematodes.”

Scott Monfort, University of Arkansas, said until better tools come along nematode management will include a combination of practices. “We have to bring ideas and tools together,” he said.

Top of that list of tools will be sampling. “That’s the most important thing,” he said. “We have to identify the species and the population density. Then we can make management decisions.”

Resistance and rotation will play key roles. “And we have to learn the limitations of available chemistry. We have to bridge the gaps among the tools available. Field identification will be a key. Research and Extension recommendations will blend with historical data to develop precision agriculture techniques.”

Mapping will be important, Monfort said, to assess damage, identify multiple species and to determine where to apply chemicals. “We need to assess thresholds across soil types and learn how to manage multiple nematode species. We need better laboratory extrapolation, increase breeding efforts and (learn to use) a combination of nematicides.”

Growers, industry, and universities have to buy in to make the programs work, he said. “Growers may need to become more aggressive with nematode control. We need to understand that nematodes may not be the only problem in a field. We should use a holistic approach that considers water, fertility, weeds, tillage practices and rotation.

“But all that will be lost if we don’t sample. It’s not that expensive and is essential for precision agriculture. We have to know where the population is. We don’t predict, we sample to make sure.”

Monfort said growers must fix other problems as they manage nematodes. “Yield monitors and mapping will help. But we have to determine if maps reflect only a nematode problem.

“Biological controls may help but we will need to use them with other products. They will not replace Temik.”