Aphids survive in cotton fields on their ability as opportunists. Populations wax and wane depending on crop conditions, availability of predators and insecticides farmers choose to control other pests. Aphids like cotton with too much nitrogen and too thin stands.
At high levels, they can take a significant bite out of potential yield.
And this year, farmers may do well to sacrifice a little yield to the pests in exchange for efficient, economical controls that prevent heavy losses late in the season.
Wait and see may be the best advice farmers can follow in a year when profit, even with near perfect conditions, could be marginal, says Texas A&M Extension entomologist Jim Leser, at Lubbock.
“Rarely, do aphids become a problem in cotton until late July or early August,' Leser says. Scouting and judicious use of selected insecticides are keys to economical control.
Leser says farmers also should follow proven cultural practices to minimize aphid populations.
“Nitrogen plays an important role,” he says. “Farmers should address the crop's nitrogen needs through the growing season. If they apply more nitrogen than target yields justify, they may see more aphid problems in July and August.”
Leser says many farmers have neglected to soil test the last few years and added more nitrogen than the crop needed. “Many will try to economize this year and lower their yield target. If they do, they need to reduce nitrogen as well.”
Leser says a uniform stand also helps keep aphid populations down. “With low plant populations, we see more aphid problems.”
Leser says some cotton stands were not uniform early because of cool, damp growing conditions. “Most will achieve full stands as conditions improve,” he says.
The most important factor in reducing aphids, Leser says, is insecticide selection.
“Don't use pyrethroids for early-season pest control. That will affect aphid populations later. We see no reason to apply pyrethroids until August in the High Plains.”
He cautions against controlling beet armyworms or cutworms early with pyrethroids, “even though they are cheap this year. Some growers may consider using them for thrips control, but we have better options.”
Leser says Larvin, a good, effective insecticide when used at the right time, also may flare aphid populations if used early. “It's hard on lady beetles,” he explains. “We have research to back that up.”
Leser says growers have Provado and Furadan available for aphid control, if they reach economic thresholds in late July or August. “Centric also may be available this year.”
He recommends farmers scout thoroughly for the pests and be cautious about applying insecticides too soon. Current treatment threshold, 50 aphids per leaf, should not necessarily trigger a spray application this year.
“Scout frequently, at least twice a week when you know aphid populations are building. Also, 50 per leaf is not a magic trigger number. We don't recommend an automatic insecticide application when populations reach that level.”
He says aphid numbers change rapidly, up and down. “We may find 25 per leaf and then 50 four days later. In another four days, population may be up to 55 or 60. Still, wait for another three or four days. If it hits 100 per leaf, I would treat.”
He says some growers may be concerned that when aphid populations reach the 50 per leaf threshold they will not be able to control them quickly enough to prevent damage.
“At that level, they are not causing much loss,” he says, “maybe $8 to $10 per acre. I would want to see 50 per leaf in consecutive checks before considering an application.”
He still recommends caution. “If populations continue to hang around 65 per leaf, we can't justify spraying this year,” he says. “We're not getting that much damage in cotton that's beginning boll-fill.”
He says farmers also need to look at beneficial insect populations, especially ladybugs, when determining when to treat aphids.
Leser advises against spraying aphids to prevent sticky cotton this year. “We have to let rain take care of washing the honey dew off the lint,” he says. “Also, mills can blend cotton to eliminate the problem.”
Leser recommends careful scouting. “Look at the whole field, not just the trouble spots,” he says. “Growers may have a tendency to check the worst areas and then skew their judgment on what's actually in the field. That goes for aphids and other pests as well.”
He recommends walking through a field and selecting test sites at random.
“Check the top-most, fully expanded main stem leaf and one in the middle of the plant. Also, learn to get a visual idea of populations. We can't take time to count 50 aphids on each leaf, so learn to identify what a cluster of 10 to 15 aphids looks like on a small part of a leaf.”
He advises farmers who do not use consultants to evaluate a treatment soon after it's made.
“If control fails, contact the applicator and correct the problem immediately. Inadequate aphid control will cause populations to explode. Treatments remove beneficials and also knock aphid numbers down without eliminating them. That spurs reproduction. Crowding actually limits reproduction.”
Leser says proper nozzle placement and type also affect aphid control. “Make certain to set nozzles to apply material down the plant stem. Also, hollow cone nozzles provide better coverage for insect control than will flat nozzles, which are preferred for herbicide application.
“Don't skimp on spray volume. It is a false economy to reduce volume and jeopardize coverage. By ground, apply at least 10 gallons of spray volume per acre. For aerial application, use 3 gallons per acre.”
Leser says aphid pressure has not been an issue early this season. “But they have seen problems in south Texas where aphid populations appear heavier than usual. We don't know what that may mean later for the High Plains.”
Editor's note: This is part seven of our Cotton 101 series, focused on producing the most efficient crop possible under challenging economic conditions. Subsequent articles will deal with late-season insect control.
Sacrifice a little to save a lot
By Ron Smith
Farm Press Editorial Staff
High Plains cotton farmers looking for ways to reduce insect control costs on what will be a marginal crop, at best, have two options, says a Texas A&M Extension entomologist.
“First, they can try season-long control with lower rates, cheaper pesticides or nothing at all,” says Jim Leser, of the Lubbock Extension and Research Center.
“Or they can follow a control strategy to avoid big losses.”
The latter probably makes more sense in a depressed economy, he says.
On one hand, farmers can ill afford to lose much to insect pests, but, on the other, they can't afford to spend a lot of money to protect a crop that may not return a profit.
“It makes sense to let the little losses go and avoid the big ones,” Leser says.
He says if growers follow treatment thresholds “to the letter,” they protect the crop from small losses. “But we can't afford to treat insects at current threshold levels this year,” he says. “We can take a little more damage.”
Currently, bollworm thresholds kick in when scouts find 10,000 per acre. “But an infestation right at threshold will not cause much damage, perhaps $8 to $10 per acre. We can live with that, if we can avoid the big losses, 100 to 200 pounds per acre.”
Leser says growers can improve efficiency with better insecticide selection and application timing, better coverage, and accurate scouting.
“But this year, we can't afford to attempt absolute control.”