The thrips calls have begun now that some cotton is starting to put out a true leaf. There are reports of multiple thrips per plant from several individuals, and I am expecting a spike in the action that often comes near the end of May. No one wants to hear it, but multiple thrips per plant or evidence of injury on the first true leaf should trigger an insecticide application. The presence of immatures at this stage should certainly trigger action. It is better to be aggressive early (before the third true leaf) than once the damage is done.
There have been several questions about what to spray. The products listed below are all labeled for thrips control in cotton. All typically provide good control. The data collected over the years suggests that, when a foliar application is necessary on top of insecticide treated seed, only one application is typically needed and it is best to make this application before the third true leaf has emerged. Making two foliar applications should be unusual and greatly increases the chances of creating secondary problems with spider mites or aphids.
- Acephate (e.g., Orthene 90S or 97SP) at 0.2 – 0.25 lb/acre: Often my first choice because it is effective, cheap, and mixes well with other pesticides without risk of significant injury.
- Bidrin 8E at 2.5-3 oz/acre: Also a good choice, although there is a little more risk of “heating up” injury caused by some herbicides. There may be less chance of flaring aphids or spider mites with this product than with Acephate.
- Dimethoate 4E at 6 oz/acre: Another option that may be less likely to flare aphids or mites. This product sometimes causes burn similar to Dual or Liberty, so I typically don’t recommend tank mixing with these herbicides.
- Radiant SC at 1.5 – 3 oz/acre: The common use rate is 1.5 oz/acre, and it should be applied with an adjuvant as suggested by the label. There is some indication that adjuvants may not be necessary if mixing with herbicides such as Roundup or Liberty, but we need more data. Radiant is the best choice if western flower thrips are common, but it is also more expensive. It may be less likely than the other products to flare secondary pest problems. Thus, I often recommend this product if a second application is required.