Mother Nature’s freezing January temperatures reduced nematode buildup in southern Georgia fields. But warmer temperatures this spring could spark nematode activity, according to University of Georgia Cooperative Extension plant pathologist Bob Kemerait.
“The great thing about this cold weather was that the soil temperature fell below 60 degrees (Fahrenheit) and even approached 40 degrees during much of January. As the soil temperature decreased, nematode activity started to drop to the point that they were not active anymore,” Kemerait said. “Now, as we enter spring and as soil temperature climbs above 60 and 65 degrees, the nematodes are happy, they’re feeding and reproducing. That’s what growers need to be concerned about.”
Root-knot nematodes cause the most problems for cotton farmers. They feed on cotton roots and cause swelling, or “galls,” to develop. The galls disrupt the function of the roots, which stunts the plant’s growth. Further, female nematodes feed and lay eggs at the galls.
Georgia farmers welcome the cooler start to 2018. Through the final days of last year, unseasonably warm temperatures enabled the growth of volunteer, or unintentionally planted, peanuts and regrowth in some corn and cotton fields. Nematodes feed at these sites in the winter if temperatures are warm enough.
“The bottom line is, if the nematodes have something to eat, whether it’s a susceptible winter crop or a suitable weed, and the soils get warm earlier than we want them to, the nematodes may be waiting when we plant seed in April and May,” Kemerait said.
Georgia growers also face a restricted supply of the nematicide Telone II, a soil fumigant, this year.
“My advice is, if you want to use Telone, make sure you know your source. Make sure you can get the supply you need,” Kemerait said.
He suggests that growers reduce Telone use through “site-specific applications,” or by applying Telone only in parts of the field that really need it. Other nematicides can be used on the remainder of the field, he said.
Where southern root-knot nematodes are a problem, cotton growers should consider planting resistant varieties that don’t need nematicides. Resistant varieties sustain minimal damage from the nematodes, and they minimize the buildup of nematodes.
“Growers sometimes balk at planting the resistant varieties because, when they look at UGA Extension variety trials, they see that the susceptible varieties yield more than the nematode-resistant varieties. I tell growers that our highest-yielding cotton varieties are probably not the nematode-resistant ones, but we’ve got great yield potential in our resistant varieties if you plant them in fields where they belong,” Kemerait said.
“With cotton, if you plant resistant varieties in a heavily infested root-knot-nematode-infested field, they will outshine the susceptible variety. When you look at resistant varieties, where they shine is where the grower is struggling to make yields because of nematodes.”