Cotton farmers are encouraged to use follow-up sprays to control thrips even if they think they’re not seeing problems with resistance, and a new tool can help them determine when to make those sprays.

The Thrips Information Predictor developed by George Kennedy, a professor of entomology at N.C. State, uses weather data to make predictions of thrips dispersal, timing and seedling susceptibility occurring at the same time. Reisig, N.C State Extension entomologist, said it is a valuable tool because it allows cotton farmers to prioritize when and where to make follow-up foliar sprays to control thrips.

“The model uses several different things but the most important thing it uses is growing degree days and planting dates because we know that our injury from thrips is a function of how fast the plant is growing and what those populations of thrips are doing in terms of migration and development. You really want to time your sprays at the first true leaf of right before that true leaf is emerging,” Reisig said at the Blackland Cotton Field Day at Southland Farms in Belhaven, N.C. Sept. 21.

Research conducted in North Carolina and Virginia suggests that using a combination of treated seed along with imidacloprid liquid directed into the open furrow on the seed before closing may provide cotton producers a “one-and-done” option for thrips control, meaning no follow-up spray is required. However, since thrips have imidacloprid resistance, N.C. State in its official recommendations strongly recommends scouting to determine if a follow-up foliar spray is needed to avoid field failures.

In most cases, Reisig said the university is now recommending farmers use a follow-up foliar spray to control thrips. He notes that his research conducted at the Vernon James Center in Plymouth and at the Upper Coastal Plain Research Station in Rocky Mount that cotton with a follow-up spray of Orthene worked best for thrips control.

Reisig says it is vital for farmers to rotate chemistries in order to prevent resistance.

“Orthene can be used as a foliar spray, but we do have another chemical that is effective,” he said. “Radiant is a different class of chemistry than Orthene. Put it in the mix because we are concerned about resistance developing. If we go with a neonicotinoid  and Orthene spray, we’re going to develop resistance to Orthene.  We do need to rotate chemistries.”