Monday, March 21, 2022

Thinking About Thrips in 2022

Insect management is different from all other aspects of cotton production. With most insect pests, the situation changes year to year, week to week, and sometimes field to field. However, one insect that we can plan on being a consistent threat every year is thrips. This pest will infest 100% of the cotton planted in Alabama every year. What we cannot always predict, however, is when thrips pressure will peak. In a “normal” year in Alabama, we expect thrips pressure to be worse on early planted cotton and to be less later in the planting window as weather conditions improve. In 2021, this was not the case. Spring rains kept weedy hosts viable for a longer period, resulting in thrips pressure being the greatest on cotton planted after the middle of May. Much of our cotton was planted in this window and nearly 75% of our acres required a foliar treatment to supplement at-plant insecticides.

We have several options for at-plant management of thrips including insecticide seed treatments, and in-furrow liquid or granular materials. There are pro’s and cons of each approach, so deciding which strategy to use may make sense for one situation and not for another.

At-Plant Insecticide Options

Insecticide seed treatments
(ISTs) are currently the industry standard for thrips control, due primarily to the ease of application. However, under certain conditions control is variable. If conditions are not conducive to seedling growth, particularly if nighttime temperatures are cool, seed treatments alone may not provide adequate control. Due to developing resistance, particularly to thiamethoxam, we recommend seed be treated with an imidacloprid based seed treatment. There are several brand names, and some include additional insecticides, but imidacloprid should be a component. Under light to moderate thrips pressure, ISTs may provide adequate control. Seed could also be treated with acephate (e.g., Orthene) or acephate could be added to imidacloprid, however in most cases a bag of over-treated cottonseed cannot be returned if not planted.

Liquid or granular in-furrow insecticide applications are another at-plant option to manage thrips. These can be used to replace or supplement an IST. In many cases, in-furrow applications provide better control of thrips, however using them requires extra equipment, proper calibration and time when planting. Imidacloprid at the highest labeled rate has consistently provided good results in our trials across Alabama in recent years. Acephate has provided more sporadic control, likely due to the wet springs we have faced over the past 2 years and leaching out the chemical before the roots can uptake the needed amount to provide control. Aldicarb, now available as AgLogic15G, is another in-furrow option. This granular product provides excellent control of thrips and provides control of nematodes as well. Keep in mind that aldicarb is a restricted use pesticide and additional training may be required to use this product.

Foliar Insecticides

Foliar insecticides may be needed to supplement at-plant treatments. However, foliar applications should never replace an at-plant insecticide. Thrips can injure seedling cotton until around the 5th true leaf stage. Research shows that foliar applications are usually most effective when made at the 1st true leaf stage. The Thrips Infestation Predictor for Cotton is a reliable tool that predicts the relative risk of thrips injury for cotton planted at a given location and planting date. To maximize the accuracy of the model, it should be run for several days before and after planting, as unpredicted weather patterns may alter the prediction. This tool should not be used to determine planting dates, but rather to help plan out fields or planting dates for cotton that will likely need a supplemental foliar application. Several options are available to use to supplement at-plant insecticides.

·         Acephate (3 oz/A) is an effective and relatively inexpensive option, however it has the potential to flare secondary pests such as spider mites and is the least rainfast of the available recommended options.

·         Bidrin (3.2 oz/A) is another option that is effective and less likely to flare spider mites and is more rainfast than acephate, however it is more likely to cause crop injury when tank-mixed with herbicides.

·         Dimethoate (6.4 oz/A) is another cost effective and efficacious product with good rainfastness, however it is the most likely to cause crop injury when tank-mixed with herbicides.

·         Intrepid Edge (3 oz/A) is another effective option. Intrepid Edge is less likely to flare secondary pests but may need the addition of a surfactant to help with efficacy.

·         Pyrethroids are not effective and should not be used to manage thrips.

Effective thrips control is critical to get the 2022 crop off to a good start. When considering areas to cutback on costs, do not skip out on at-plant (IST or in-furrow) insecticides. We cannot manage thrips without having protection for the seedlings as soon as they emerge. If planting into cool, wet conditions, be prepared to make supplemental foliar sprays to help seed treatments get seedlings to the 5th true leaf stage. More information about thrips can be found in Pests of Alabama Cotton: Thrips (ANR-2718). For more information on thresholds and insecticide recommendations, visit the Alabama Cotton IPM Guide (IPM-0415). To stay up-to-date on the Alabama cotton insect situation, subscribe to the Alabama Cotton Shorts Newsletter, Alabama Crops Report Newsletter and Podcast, and the Syngenta Pest Patrol Hotline.