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With more cotton starting to square, ALL cotton in the state should be scouted so that we maintain acceptable square load to bring us into blooming (see this previous article for how to scout and use thresholds for plant bugs prebloom). Dr. Sally Taylor, VA Tech, has been performing bioassays with tarnished plant bugs from Virginia and Northeast North Carolina. Her results confirm my insecticide trial results and what growers and consultants see in the field. Insecticide performance is variable across our region, making it hard to prescribe a program with a broad brush. Even though I think that growers and consultants should design a program that works for them, here are some general guidelines for selecting an insecticide.
Prior to bloom, we recommend an insecticide in the neonicotinoid-class, such as Centric, but growers should avoid Admire Pro and Trimax Pro (imidacloprid; discussed later). The advantage to using these products is that they generally do not flare secondary pests, such as spider mites, and may preserve some, but not all, beneficial insects. In general, a product that is killing a plant bug will likely kill related beneficial insects such as minute pirate bug and insidious flower bug, damsel bugs, assassin bugs, and big-eyed bugs. However, these products are still much less harsh on the system than pyrethroid and organophosphate-class insecticides. Don’t forget that an apparent “spray failure” early season could be a situation where you are chasing adults. That is to say that adults could have re-invaded into the field after spray, making it look poor, when in fact it worked. Check sprays as soon as it’s safe to enter the field.
Some folks have been choosing Admire Pro as a first insecticide, but our data do not support the efficacy of this insecticide over Centric. In my screening trials, Admire has always looked as good as other alternatives or, in other cases, worse. Furthermore, in a recent trial in South Carolina alfalfa, Admire was especially weak on plant bug nymphs. Finally, using an insecticide that exceeds the labeled rate is not only illegal, but it increases resistance in the target pest and non-target pests (we already have populations of neonicotinoid-resistant aphids). To be clear, our recommendation is Centric as a first insecticide prior to blooming. Do not spray neonicotinoids as stand-alone treatments after June.
Later in the season, neonicotinoid efficacy tends to fall off. While our past recommendation has been a pyrethroid, resistance to this class of insecticides is becoming more widespread. Therefore, to be certain of efficacy, pyrethroids should be avoided or tank mixed with other classes of insecticides.
If nymphs are present, you should consider mixing in Diamond at 6-8 oz. Diamond is an insect growth regulator and only directly active on immatures (hatch rate is reduced in eggs from adult females exposed to Diamond), so it needs to be paired with an insecticide for knock down of adults. Data from the Midsouth shows that it can extend the time that they have to make their next spray and is worth the investment. In areas that are pyrethroid resistant, mix Orthene with Diamond, except before a bollworm flight.
Another tool in our arsenal is Transform. My trials support the use of this product at 2 oz or higher, but not at 1.5 oz or lower. A huge advantage of this insecticide is that it is softer on beneficials than many other products- don’t be tempted to tank mix other chemicals with this insecticide that might hamper this benefit! Transform is the insecticide that growers should reach for prior to a bollworm flight.
Finally, don’t forget about other insecticides and mix combinations that might be helpful post-bloom and later season, such as Bidrin, Vydate, and tank mixes of pyrethroid and Orthene, pyrethroids and neonicotinoids, etc. As we’ve learned time and time again, pesticide rotation is a major key to long term success.