North Carolina Cotton: Check for Plant Bugs at 1st Square

    Tarnished plant bug. Photo: University of Georgia

    Cotton should be scouted for plant bugs from the time it squares until the last harvestable boll is formed. You can visit the cotton scouting guide for detailed information, but below are some quick recommendations for scouting and treatment in cotton prior to bloom:

    Last year Dr. Mohammad Amir-Aghaee’s experiment showed the value of protecting squares early. These data also highlight the fact that you cannot afford to leave plant bugs untreated when they are above threshold.

    Using an insecticide that wasn’t particularly effective, it was still more profitable to spray early and often for this insect in this trial.

    Number of insecticide sprays for tarnished plant bug and timing of treatment (note that both low and high thresholds were triggered and these treatments received 6 total sprays). Click Image to Enlarge

    Prior to blooming, use both a sweep net and monitor square retention to make a treatment decision. No point treating for squares that are dropping with no plant bugs or treating plant bugs that aren’t knocking off squares. Use the threshold of BOTH 8 plant bugs in 100 sweeps AND 80% square retention to treat.

    Don’t just monitor squares in the terminal. Be sure to check squares farther down the plant, as bugs will move up and down in the canopy.

    Check probable hosts near your cotton to get a feeling for what might move into your field. Plant bugs can develop on hundreds of plants, but big hosts in our environment are corn, weeds, like daisy fleabane, and in the northeast, potatoes and clary sage.

    Check field edges and field middles. Plant bugs are notorious for spotty distributions and moving around even within a single day.

    If you must spray, use a full-labeled rate of a chemical in the neonicotinoid insecticide class at this point in the season. Common active ingredients in this class include clothianidin, imidacloprid, or thiamethoxam. CHECK THE LABEL to find out the active ingredient and rate.

    A quick note on insecticides. Neonicotinoids work early season, but fall out later. Usually “spray failures” from neonicotinoids early season are not actual failures, but are adults that remigrated in right behind a spray. This would’ve happened with any insecticide that was used.

    By using neonicotinoids as an initial application, it allows us to rotate to pyrethroids later in the season. This is one of the big ways we can prevent insecticide resistance.

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