As an update to the article below, reports of multiple thrips per plant are becoming more common. This is expected as seedling plants get larger. Once past the third true leaf, there is generally little or no benefit to treating for thrips except under unusual circumstances. One of these circumstances would be when thrips infestations were not previously well managed (e.g., when infestations should have been treated during the 1-2 leaf stage). The benefits of foliar insecticide applications for thrips control are sporadic, and almost all the data would suggest that any positive impact on yield is observed when these applications are made by the second true leaf stage. Once this application is made, the value of a second application is questionable, though evidence of thrips injury will often persist. There are possible exceptions. We are again seeing indications that Cruiser (thiamethoxam) seed treatments are not performing particularly well, and this would be a situation where I wound consider making two foliar insecticide application by the time the third true leaf is emerged.
Many people have commented about a perceived lack of control, where thrips numbers rebound quickly after treatment regardless of the insecticide used. This should be expected when populations and movement are high. Keep in mind that “knocking thrips back” for just a few days is often all is takes to get seedlings past the very susceptible 1-2 leaf growth stage. Be comforted that these application do have a benefit.
As more and more cotton is coming out of the ground, thrips management will be on people’s mind. Most folks are currently reporting that thrips pressure is average. Because of concerns about the performance of insecticide seed treatments, my standard recommendation will be to make a foliar application to cotton, preferably by the time the second true leaf has emerged. There are several options listed in the table below. Radiant would be a preferred choice if western flower thrips are present in substantial numbers. However, this product is relatively expensive, and I have no reason to think western flower thrips are more common than usual. I would consider using Radiant for follow-up applications, when needed, because this product appears less likely to flare secondary pests like aphids and mites. Also, western flower thrips will be usually be a bigger portion of the thrips population following an application of other products.
Many of these applications will be tank mixed with herbicides. UT data suggests that Dimethoate will cause some leaf burn/spotting, similar to Dual products. Thus, I would avoid Dimethoate if spraying products such as Dual or Sequence because they may add to any leaf burn caused by the herbicides. Similarly, I would avoid Dimethoate if spraying Ignite on WideStrike cotton. Larry Steckel and I have done several tests which indicate there is very little risk of compounding leaf injury by adding Acephate or Bidrin to Ignite or herbicides containing Dual. However, the herbicide injury will often still be apparent. Radiant should also mix with these herbicides without any additional risk of injury.
Suggested insecticides for foliar applications to control thrips.
|acephate 90S or 97SP (Orthene)||0.18 – 0.25 lb ai/acre|
|dicrotophos (Bidrin 8)||1.6 – 3.2 oz/acre|
|dimethoate 4||4 – 8 oz/acre|
|spinetoram (Radiant SC 1)*||1.5 – 3.0 oz/acre|
* For Radiant, the standard use rate is 1.5 oz of product per acre, but the use of a adjuvant/surfactant is strongly suggested for this product (see label). The surfactant load present in many herbicides such as Round Up, Sequence and Liberty may suffice, but this has not been extensively tested.