Recommendations For Thrips Management In The Missouri Bootheel

CHASE FLOYD

COLUMBIA, MISSOURI

 The majority of Bootheel cotton acreage has emerged, and phone calls are coming in with inquires on how to manage thrips. Sadly, 2024 has not been an ideal year for thrips management due to the consistent overcast during the daytime hours. This restricts thrips movement, and in hand can increase injury. Hot and sunny conditions are ideal not because thrips are more active, but because cotton and growth development occur more rapidly, and we can reach the 4th true leaf stage where our cotton can out run thrips injury.

I just wanted to highlight some management options for thrips control in 2024.

ThryvOn varieties

ThryvOn is Bayer’s Bt technology designed to have activity on thrips and plant bugs. ThryvOn varieties are highly efficacious against thrips and foliar applications for thrips will likely not be warranted. If scouting ThryvOn varieties be aware that thrips, both adult and immatures will both be present, but insecticide applications should not be considered on thrips numbers, but damage level (Fig 1.). Applications should be initiated when plant damage resembles the damage rating 3 in the figure below. With that said, my colleagues and I across that cotton belt have looked at ThryvOn varieties for several years, and no one has yet to recommend a foliar application to any ThryvOn.

Insecticide Seed Treatments (IST’s)

ISTs are the primary control method for thrips in cotton. Weather conditions and thrips pressure greatly influence the variability of IST performance. High thrips pressure and poor growing conditions will often warrant foliar sprays to cotton implemented with IST. In the Bootheel the use of wheat as a cover for sand blasting naturally puts us in a higher thrips pressure scenario. Typically, preemergence herbicides whether behind the planter or an over-the-top application will begin the process of drying wheat down making it an unfavorable host for thrips right as cotton begins to emerge. Thrips will then move directly to the closest favorable host. Seed treatment packages commonly come in a base (storage rate of imidacloprid + fungicide) and field rates of imidacloprid + fungicides, other may include various nematicides and or biologicals. Base seed treatments including the small stored product rate will offer almost no control of insects in field scenarios. At minimum, imidacloprid at a rate of (0.375 mg ai/seed) are the minimum needed to have any sort of control in field cotton.

In-furrow thrips applications

We see higher success across the belt with in-furrow liquid applications of imidacloprid compared to our seed treatments. However, thrips resistance development to the insecticide class of neonicotinoids is beginning to diminish the efficacy for imidacloprid in-furrow. It is likely that in-furrow imidacloprid applications will require a foliar spray in the Bootheel. Prior to ThryvOn release, in Mid-South in-furrow thrips trials, granular Aglogic (aldicarb 15G) was the gold standard for thrips control. In my 2023 trials, AgLogic was significantly greater in controlling thrips than all other applications of insecticide whether applied in-furrow or as a seed treatment. Only plots implementing a ThryvOn variety were able to reduce thrips populations numerically lower, but no significant differences were observed. Lack of utilization of Aglogic in-furrow today, is the lack of dry insecticide boxes equipped on newer planter setups. Its price per acre can also be a downside.

Foliar thrips applications

There are limited foliar options that are efficacious for thrips control in cotton. We sampled a population of thrips near Holcomb, Missouri in 2023 and had bio-assays performed to monitor thrips resistance to organophosphates (OPs). Results from these populations showed that our commonly applied Ops, Acephate and Bidrin could only reduce thrips populations by 37% and 80%, respectively. Note that this is only one population, and other areas may have greater success or failures with these OP applications. The biggest issue with OP applications in the Bootheel is there is always a chance, to flare spider mites. Due to our higher sand content in the Bootheel’s cotton growing soil types, precipitation can move through our soil profile making our environment dry and conducive to spider mites. If we have spoken about applying OPs for thrips control this year, note that I typically check the forecast during our call. This is due to the likelihood of higher humidity post application if precipitation is in the forecast. Humidity can play a role in the suppressing thrips. If forecasts predict hot and dry weather conditions in the near future, I typically I will avoid applying OPs if possible.

With that being said, I have very little stipulation when wanting to utilize Intrepid Edge for control of thrips. Price needs to be taken into consideration when applying Intrepid Edge since it is a more costly application compared to the OPs. The benefits of an Intrepid Edge application is no risk of spider mite or aphid applications when applied, and was the only product tested in bio-assays to provide 100% control regardless of where you are in the cotton belt. Adding a surfactant preferably and oil has shown to increase efficacy, this applies to herbicide surfactants if you are tank mixing. If you are applying Intrepid Edge standalone, consider selecting a finer droplet nozzle to increase the number of droplets per area to increase efficacy.

If considering making an Intrepid Edge application regardless of tank mix 3 fl oz/a need to be applied.

The biggest question I am asked is the residual of Intrepid Edge, I will say 3-4 days of protection is all you are going to get. Which is much greater than only getting initial knockdown with an OP application.

One of the more critical points of managing thrips in cotton is understanding Recolonization vs failure of a foliar thrips application. If you are picking up adult thrips following a foliar application, this does not mean the product failed. Adult thrips will always be on seeding cotton due to constant wind dispersal which we are familiar with in the Bootheel. When immature thrips are identified following applications, this means adults are actively feeding and laying eggs on the plants, and your foliar application is no longer providing benefits.

If you have any questions concerning thrips management decisions, please do not hesitate to reach out at (901) 493-2377. We can discuss any scenario; I am here to help! Let’s get to 4th true leaf and start preparing for plant bugs! ∆

CHASE FLOYD: University of Missouri