Mixing Thrips Insecticides With Post Herbicides: Yes or No?

We have been getting a lot of questions the last 7 to 10 days about potential injury or problems associated with mixing thrips insecticides with POST herbicides over cotton. This will no doubt be controversial, but we are going to lay it out like we would if you called.

To start, we are primarily talking about three herbicides that are used most commonly over the top of cotton during the “thrips stages”. These are acetochlor (Warrant), glufosinate (Liberty 280), and metolachlor-based products (Dual Magnum, Sequence, etc.) applied alone or sometimes in mixtures with glyphosate.  Also, what comes into question is if the Liberty 280 and combinations are going out on true LibertyLink, Glytol/LibertyLink varieties or on WideStrike varieties.

We have evaluated numerous insecticide/herbicide combinations over the years across the whole Midsouth region for compatibility and crop safety. While we cannot guarantee every adjuvant/herbicide/insecticide combination, we have certainly evaluated the most likely combinations.

Take Home: Metolachlor-based products, Liberty 280 (on WideStrike cotton), and Warrant can and will often burn (injure) cotton without any insecticide in the tank. Burn is nearly always cosmetic and poses no risk to yield. The addition of an insecticide can sometimes enhance the burn but rarely above the herbicide’s own injury potential. There are four insecticides we recommend for thrips control; Acephate, Radiant, Bidrin, and Dimethoate. Acephate and Radiant are the safest followed by Bidrin. In fact, Dimethoate is the only one in the group that consistently causes any additional burn when mixed with herbicides, and this is rarely severe.

The reason herbicide/insecticide mixtures are controversial is everyone has a story about a time when they burned cotton when an insecticide was in the tank. Chances are you would have burned the cotton anyway from the herbicide alone.

One true exception is the addition of a metolachlor-based product or Warrant with Liberty 280 on WideStrike cotton. This is the hottest combination we have evaluated and IT IS worse when mixed with Dimethoate or Bidrin. However, we are perfectly fine with mixing the insecticide alone with either Liberty 280 or metolachlor/Warrant, but not in combination.

No one likes walking injured fields trying to determine the cause, so the simple answer you will hear most often is do not mix the insecticide with the herbicide. Fact is, I would not hesitate to mix one of these thrips insecticides from an injury standpoint and save the money on application fees, but for specific questions please give one of us a call.

Photos below by Dr. Jason Bond show examples of injury you may see with various herbicides and insecticide mixtures.

CLICK TO ENLARGE:

Roundup PowerMax at 22 oz/A + Dimethoate at 0.5 pt/A

Roundup PowerMax at 22 oz/A + Dual Magnum at 1 pt/A

Roundup PowerMax at 22 oz/A + Liberty 280 at 29 oz/A + Dual Magnum at 1 pt/A + Dimethoate at 0.5 pt/A