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 5^th true leaf stage. Research shows that foliar applications are usually most effective when made at the 1^st 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 5^th 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.

What Did We Learn about Cotton Insect Management in 2021?

Several cotton insects presented unique or unusual infestation patterns in 2021. The following is a discussion of insects as they occurred during the season and what we may want to consider as we enter the 2022 crop year.

Cotton seedlings showing varying thrips injury in 2021.

Thrips, for the second season in a row, reached their peak injury period in late May to early June. Therefore, the heaviest damage was to cotton planted after about May 10-15. Growers should be alert and protect all seedlings from thrips injury until plants reach about the 5th true leaf. This can be done by applying a timely foliar spray when seedlings are at the 1st true leaf. The Thrips Predictor Model, developed by NC State with research data from all Southeastern states, is very useful in alerting to potential injury in this late planting window, especially when it is run weekly until all seedlings are safe from injury. This phenomenon of thrips damage on late planted cotton is likely driven by frequent rainfall in the early to mid-planting window. Excessive rainfall tends to sustain and keep lush wild host plants that harbor thrips, thus delaying their movement to cotton.

Plant bug infesting 7 node cotton in Belle Mina, AL in 2021

A second pest that presented an unusual infestation pattern last year was tarnished plant bug. A heavy, statewide movement of adult plant bugs from wild hosts to cotton occurred between June 13-15. Reports and observations about plant bug migration came from Central Alabama, Tennessee Valley, Gulf Coast and Wiregrass during this 72-hour period. This movement, had it been from one specific area, would have been expected, but the fact that it occurred statewide within a short time had never before been observed or reported. All available media, social, electronic and telephone hotline, were employed to alert agents, field advisors and farmers. These early season adult plant bugs immediately began feeding in young squaring cotton, causing pinhead square loss in the early fruiting window. At the same time, female adults were depositing eggs into the tender stems of cotton, producing a hatch of immature plant bugs 3 weeks later in cotton between weeks 1 and 3 of bloom. Where timely controls were not made, “dirty” blooms resulted, and yields were reduced.

Stink bugs can cause damage until bolls are ~25 days old.

One other insect, stink bugs, should be part of this discussion. Stink bugs were more numerous than expected last season following what we thought was a colder than normal winter, including a particularly cold week that occurred in mid-February. We realize that though stink bugs have been our number one most damaging insect in cotton for the past 25 years, we are still refining or fine tuning our control strategies. One observation made in 2021 was that mid to full season varieties may require an additional late season application as compared to early maturing varieties. Basically, stink bug controls are warranted until the uppermost bolls – top bolls that are expected to be harvested – are about 25 days old and hard to the touch. During boll fill, a stink bug application should give about 2 weeks control or suppression except in field borders adjacent to corn, peanuts, pecans or other alternate stink bug hosts. After stink bugs enter cotton, beginning about the 3^rd week of bloom, any applications targeting plant bugs should include an insecticide or tank mixture that controls both pests.

Take Home Point:

The take home message from these occurrences is that growers and other ag advisors must be aware of more than just what they see in local fields. They must be “in the loop” from a bigger perspective in order to be alerted to unusual insect outbreaks. The Alabama Extension Cotton Entomology team has lots of eyes and ears throughout the state and receive daily and weekly feedback that can be passed along to all involved.

Ways to stay in the loop:

Syngenta Pest Patrol Hotline

Alabama Crops Report Newsletter and Podcast

Alabama Cotton Shorts Newsletter

AgFax Seasonal Crop Reports (Subscribe to Southeast Cotton)