Don’t Wait to Control Thrips in Cotton

Left unchecked, thrips can slash several hundred pounds from cotton yield potential. Both common tobacco thrips and the increasingly prevalent western flower thrips can be controlled for up to three weeks with insecticide seed treatments. Acceleron® Applied Seed Solutions for cotton contain imidacloprid for early-season control of thrips. Over-the-top insecticide treatments may be necessary to control thrips until cotton reaches the fifth true leaf stage. Entomologists across the Southeast encourage growers to begin scouting for thrips as soon as cotton seedlings begin to emerge.

“Thrips will start infesting cotton the day it emerges,” says University of Georgia entomologist Phillip Roberts. “They start feeding on the lower surface of cotyledons and then in the terminal bud of developing seedlings. We encourage using a preventive seed treatment at planting, followed by an over-the-top insecticide as needed.” (P. Roberts, personal communication, April, 2013)

For Georgia cotton growers, Roberts recommends two different approaches to spraying for thrips on cotton seedlings. “If growers plant before May 10 and use a seed treatment in conventionally tilled fields, they should spray to control thrips when the first leaf emerges,” he says. “When cotton is planted after May 10, or in conservation-tilled fields, we encourage growers to scout for thrips before spraying. Systemic foliar insecticides should be applied to cotton which had an at-plant systemic insecticide when 2-3 thrips per plant are counted and immatures are present. The presence of immatures suggests that the at-plant systemic insecticide is no longer active. If no at-plant thrips insecticide was used, multiple well timed foliar applications may be needed.”

Roberts encourages growers to make insecticide applications as soon as thrips reach threshold levels. “Don’t put it off so you can piggy back the insecticide with a herbicide application,” he cautions. “If you have threshold numbers of thrips at the one-leaf stage, waiting only 3-5 days until the second leaf emerges can result in significant loss of yield potential. Scouting and insecticide applications as needed should continue until cotton develops the fourth true leaf.

North Carolina State University entomologist Dominic Reisig also encourages cotton growers to be particularly vigilant in scouting for thrips in April and early May planted fields. “Cooler soils and slower growing cotton allow thrips to feed longer on slowly developing seedlings,” he says. (D. Reisig, personal communication, April, 2013)

Reisig also encourages growers to carefully monitor how effectively any over-the-top insecticide controls thrips. “Orthene® will take out tobacco thrips. If the Orthene does not seem to be effective, then western flower thrips are probably in the field. Growers should then spray with Radiant® to control the western flower thrips. Remember, too, that pyrethroids are ineffective against thrips.”