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 carefully 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 aphid problems, 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.”