How to Nail 2024 Thrips Management (Reisig, Huseth)

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With planters rolling soon, we urge growers to think about thrips management now. The best source of information for timely thrips activity is the Thrips Infestation Predictor. This online tool forecasts risk for thrips damage throughout the spring. Based on which planting dates are at greatest risk, it can help growers know where to aggressively use in-furrow or foliar insecticides and where to hold back, as well as where they might want to start scouting first on the farm.

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. We also want to demonstrate why it’s so important for growers to check the tool for their farm.

Here is the risk forecast for planting cotton near Roanoke Rapids (model run 4-23-24):A chart showing increased Within-Season Risk in late may.Cotton risk for thrips damage ranging from green (low risk) to red (high risk)

However, the model we ran for Red Springs was very different on the same date:A graph showing increased risk between 5/11 and 5/21.Cotton risk for thrips damage ranging from green (low risk) to red (high risk)

These differences highlight the fact that predictions for locations can vary, depending on the year. In this case, the timing of thrips pressure in Red Springs (near Fayetteville) was very different from Roanoke Rapids, a distance of approximately 150 miles. Based on the forecast on 4-23-24, cotton planted at the beginning of May is at less risk for thrips injury than cotton planted in the middle of May (green = lower risk, red = higher risk) at Roanoke Rapids, but almost all May planting dates are high risk at Red Springs. Also, this forecast is based on expected weather, which we all know can rapidly change. We do know that the accuracy of weather forecasts improve considerably within approximately 7-10 days. As a result, it really pays to check this tool frequently to get up-to-date information for different planting dates.

Growers planting in higher-risk conditions 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). 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.

This article provides a good overview of how seed treatments, environmental conditions, and thrips populations interact in relation to efficacy. Note that acephate (Orthene) resistance was documented in northeastern North Carolina during 2023. Therefore, growers in other parts of the state should use acephate with caution this year and check behind sprays. Growers in the Northeast should follow these recommendations listed under “a suggested plan forward”. Note that if growers choose to use spinetoram, they should add a non-ionic surfactant to improve control.