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Thrips predictor hones cotton plans

The N.C. State University Thrips Infestation Predictor is based on local weather forecasts, and accuracy improves closer to planting. Growers should check it just prior to planting.

Farm Press Staff

April 25, 2024

3 Min Read
Cotton seedling
Brad Haire

Cotton planting fast approaches North Carolina cotton farmers. Extension entomologist Dominic Reisig urges them to use the Thrips Infestation Predictor, an online tool that forecasts risk for thrips damage throughout the spring.

“Growers should check this tool now to get a feeling for thrips pressure for a given location and planting date. Also, since it’s based on local weather forecasts, the tool’s accuracy improves closer to planting, so growers should check it just prior to planting, as well as after planting to understand which fields are at greatest risk for elevated thrips pressure,” Reisig writes in an Extension posting.

Reisig notes that cotton farmers planting in higher-risk conditions for thrips may want to consider an in-furrow insecticide overtop their seed treatment. In contrast, growers planting in lower-risk conditions could consider using a seed treatment alone.

“In addition to driving resistance and hurting the wallet, unneeded insecticides can sometimes cause other problems later in the season, like aphids and spider mites. After emergence, all growers should scout all fields and be prepared to spray based on established thresholds (two immatures per seedling),” Reisig writes.

“We suggest scouting the fields at highest estimated risk first. Remember that the tool can be used to hindcast risk in the past, meaning you can reassess which fields were planted into risky windows when prioritizing scouting activities. Note that insecticide sprays for thrips typically work best when you can peel back the cotyledon and see the first true leaf poking out. After several true leaves have expanded, thrips sprays have diminishing benefit.”


Reisig notes that acephate (Orthene) resistance was documented in northeastern North Carolina in 2023 and he urges cotton farmers in other parts of the state to use acephate with caution this year and check behind sprayers.

For farmers in northeastern North Carolina, Extension Reisig recommends switching to spinetoram (Radiant) at 3 fluid oz plus a surfactant to ensure adequate coverage for thrips control. He notes this is one of the rare instances where a surfactant can boost insect control.

“In addition to being effective for tobacco thrips, this insecticide has the advantage of being very strong on western flower thrips that is sometimes present in our fields. Spinetoram is also in a different insecticide class than acephate (Orthene). Other insecticides like dicrotophos (Bidrin) and dimethoate are in the same insecticidal class as acephate and are not good rotational partners. This is especially true if we suspect resistance to organophosphates, like acephate,” Resig writes in a previous Extension posting.

Reisig urges all farmers to scout for  thrips before making an insecticide application and to check for efficacy after an application.

“Pull up seedlings and tap them against a white paper. Adult tobacco thrips are small and dark. Immature thrips are even smaller and cream colored. With good eyesight you can see them moving,” Reisig writes.

“Immature thrips are a potential indicator that the insecticide spray might not have worked well. Adult thrips could have moved into the field after the spray and are not good indicators of efficacy. Finally, even with our most effective insecticides, we often find immature thrips on the plant, but at vastly reduced numbers.”

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