• By Amanda Huber,
Southeast Editor •
Thrips are the most consistent pest in cotton each year. So, it was a surprise to University of Georgia Extension Entomologist Phillip Roberts when he found out some farmers looking for ways to cut input costs were not protecting the crop from thrips.
“We see such a reliable yield response to using something at planting for thrips that I thought it was a given,” he says. “It’s just a good idea to put something out to protect the crop early.”
Support From Yield Studies
Thrips feed on leaves and terminals of seedling plants, thereby stunting growth and delaying maturity. Damaged leaves appear crinkled on top, and lower surfaces will often have a silvery sheen. Leaf margins become cupped, and terminal buds may be destroyed.
Economic damage from thrips rarely occurs once seedlings reach the four-leaf stage and are growing rapidly. Therefore, it is important to make thrips decisions at planting or very early on.
“Thrips are the most consistent pest you’re going to have in cotton,” Roberts says. “You’re going to have them every year. Use something at planting for thrips.”
The Georgia entomologist has years of field trials to back up his recommendations.
“In 44 out of 50 trials conducted between 2002 and 2014, we saw a yield increase for an average of 195 pounds of cotton per acre. If I updated the trials, it would be the same — an at-plant treatment for thrips increases yield.”
Scouting A Must
Preventive insecticides are recommended at planting to reduce thrips infestations and seedling injury. Supplemental foliar insecticides are needed in some environments, and applications should be based on scouting and thresholds. Seedlings become more tolerant to thrips feeding in terms of yield potential with every true leaf they put on. One-leaf cotton is much more susceptible to yield loss than three-leaf cotton.
“The most important dollar you can spend managing pests is to hire yourself a scout,” Roberts says. “If you’re not going to hire a scout, you’ve got to make the time to do it yourself, and you’ve got to be disciplined about doing it.”
Weather Affects Seedling Growth
Weather also plays a part in thrips pressure. If conditions are warm and moisture is adequate, seedlings should grow through the thrips susceptibility window and to the four to five true leaf stage quickly.
“If conditions are dry and plant development slows,” says Keith Edmisten, North Carolina Extension cotton specialist, “preventative control measures may be necessary.
“We recommend protective treatments of acephate at 4 ounces or Radiant at 3 or more ounces on susceptible cotton at cotyledon or first true leaf stage.”
Once cotton has put on five leaves, thereby exiting the susceptibility window, foliar applications have limited benefit to reduce damage caused by thrips.Like Roberts, Edmisten says there is more bang for the buck when sprays are applied earlier in the susceptibility window.
“It should be a given to use something at planting for thrips. Seed treatments have their place, but if thrips numbers are significant, seed treatments aren’t enough,” Roberts says.
“AgLogic 15G is an option for granular aldicarb applied in the furrow. In-furrow liquid options include Velum Total or other imidacloprid products, such as Admire Pro, or acephate products.”
Roberts says the need for supplemental foliar insecticide depends on the severity of thrips infestations, the at-plant insecticide used and the rate of seedling growth. The threshold for thrips is two to three thrips per plant with immatures present. The presence of numerous immature thrips suggests the at-plant insecticide is no longer providing control. Foliar spray options include the systemic insecticides Orthene, Bidrin and dimethoate.
Because thrips are a predictable pest in cotton and application of an at-plant treatment nearly always offers a yield increase, Roberts says this is one area growers should not eliminate to reduce costs.