Rotation is limited, says Terry Wheeler, Texas A&M plant pathologist at the Lubbock Research and Extension Center. "Grain sorghum is a host. Peanuts help, but farmers can’t put peanuts on enough acres to do much good."
On top of that, nematodes, primarily root knot species, possess an incredible ability to survive. "We can reduce numbers with rotation and chemical options," she says, "but a fair number of eggs left in the soil can hatch and create a population explosion. In fact, following a five-year stretch with a non-host crop, we still get blasted by root knot nematodes."
Dry soil is the key, Wheeler says. "But we can’t afford to leave irrigated fields fallow. We have a long history of root knot infestation in cotton.
"Farmers routinely use Temik to reduce populations, but that only works for a few weeks. That’s why we’ve been interested in developing a resistant or tolerant variety."
Wheeler says Stoneville’s new 5599 BR could be a good first step. "We started looking at this variety in 2000," she said during a recent tour of the Stoneville research plots in Idalou.
"Tests show this variety produces top yields, from 100 to 291 pounds more than the standards. Even under bad field conditions, poor management and bad weather, 5599 BR maintained a yield advantage. It’s done well under all conditions. Although not as resistance as its parent, it shows good tolerance."
Steve Calhoun, research station manager for Stoneville, says 5599 BR "routinely tops yield tests. With limited Temik rates, yield damage is still relatively minor."
Farmers need the help.
Gaines County farmer Ronnie Wallace has noticed weak spots in his cotton fields for years. "I usually see areas where cotton gets only about one foot high. I did not see that this year in a field of 5599 BR."
Wallace also uses Nemacur to reduce populations. "I apply it as a liquid at planting," he says. "It seems to work better than other materials for nematode control. Sometimes I’d need a second shot to do the job."
A tolerant variety would improve his odds, he says. He normally rotates, often with peanuts, but says in fields where he’s forced to plant cotton behind cotton, a tolerant variety would be ideal. "We have no other nematode tolerant options."
"Temik helps, but I need at least five pounds," says Steve Furlow, Terry County farmer. "Nematodes are a significant factor in this area. I can’t find a field without big populations, especially in sandy soils.
"Also, in fields that have been in cotton for 40 years the risk from nematodes increases. A lot of folks are looking for a nematode tolerant variety."
Furlow likes to plant late to avid cool weather and seedling vulnerability to nematode damage.
Edward Fisher, Sudan, Texas, uses 3.5 pounds of Temik under cotton. "That’s about all we can do," he said. "We don’t rotate. We used to raise corn but we have too little water. A few farmers have tried sesame to reduce nematode numbers and some have had good results."
Without Temik, Fisher says, yields would drop by a half-bale or more.
"We don’t plant cotton without Temik," says Dennis Flowers, manager of the Farmers Co-Op Association of Sudan, and Fisher’s crop consultant. "With heavy pressure, we add five pounds."
Fisher and Flowers also are looking at 5599 BR.
Walter King, Terry County farmer, says rotation once played a more important role in his cotton operation. "We used wheat, watermelons or grain sorghum," he says, "but market conditions have changed. We don’t follow a strict rotation. Instead, crop selection depends on program options, cash flow needs and markets."
"A tolerant variety would be an advantage," King says. "We’ve been hurt in the past by nematodes. We always apply 3.5 pounds of Temik and give the cotton the best shot we can."
Wheeler says the best shot farmers have may come from resistant or tolerant varieties.
"Fumigants work in some locations, but I have questions about whether we can do a lot with them," he says. "For one thing, we don’t have much experience applying fumigants. We could have trouble finding applicators with enough experience to apply the materials properly."
She also says the trend to minimum or no-till cotton makes fumigation less useful. "The process shows a benefit in clean-field production," she says. But getting the chemical into the soil through a cover crop poses difficulties.
"And we encourage reduced tillage systems here, especially on sandy soils that blow in the spring and damage cotton seedlings."
She says applying fumigants in cool temperatures also minimizes efficacy.
Wheeler says she has seen evidence of another potentially devastating nematode, Reniform, but believes potential for significant damage is less than for root knot.
"It’s (Reniform) around, especially in the New Home area, and it can spread all over the High Plains. But it prefers heavier soils, so it’s a low priority for research."
Wheeler says fields with Reniform populations can be "stunted severely."
She says infestation levels remain less than 1 percent, compared to 40 percent to 50 percent for root knot. "It’s been here for decades but it has not spread the way it has in the Mid-South."