Unlike pigweeds or plant bugs, nematodes are an out-of-sight, out-of-mind pest. Left untreated, however, this parasitic organism in the roots of a cotton plant can substantially reduce cotton yield. Resistant cotton varieties are becoming more critical in combatting this pest.
In west Texas, variety choice is more important than chemical control of nematodes because variety response is more consistent year after year than chemical response, according to Terry Wheeler, Texas A&M University plant pathologist. “Root-knot nematode occurs in about 40 percent of our cotton acreage, and reniform occurs in less than 1 percent. Our resistant cotton varieties are resistant to root-knot.
“Several partial-resistant cotton varieties have been available for several years, including ST 4946GLB2, PHY 367 WRF, and FM 2011GT,” Wheeler says. “Additionally, several newer varieties offer the full resistance package, including PHY 417 WRF and the PHY 427 WRF. I have yet to test Deltapine’s full season varieties, DP 1454NRB2RF and the DP 1558NRB2RF, in a full season environment.”
Wheeler describes partial resistant varieties as having a 50 to 70 percent reduction in nematodes relative to susceptible varieties. The full package of resistance decimates the nematode population dramatically by the end of the season. “If you have a serious root-knot nematode problem, you probably should consider planting the fuller resistant varieties,” she says.
“However, you can’t just consider varietal nematode reduction. Some of the partial resistant varieties can give growers a better yield potential and fiber package than some of the newer resistant varieties in some cases. You need to consider nematode reduction, yield potential and fiber quality when considering variety selection.”
If growers are not having success growing some of these nematode-resistant varieties, they can try a unique cultural method. With water being so light the last few years, several west Texas growers are windshield wiping their pivot circles, concentrating their limited water on cotton planted to half the circle.
“Some rotate the other half of the circle to winter wheat and harvest it, fallow the land the next summer and come back with cotton the following year,” Wheeler says. “It’s a terrific way to reduce nematode populations, and it allows you to plant essentially any cotton variety you want coming out of that wheat rotation.”