North Carolina Cotton: Plant Bugs – To Spray or Not to Spray?

    "Black flag" terminal damage in cotton caused by plant bugs. Photo by Webster Harrell.

    Although it looks like plant bugs may be again be an issue in 2015, we don’t need to panic.  What I mean by don’t panic is that we shouldn’t spray if it’s not needed.  Growers in the Midsouth contend with plant bugs at much greater densities and frequencies than we do.  Managing plant bugs is as easy as any of our other pests if you have a scouting plan and stick to it.  At least go out and look to see what is in your cotton before you decide to spray or not spray

    I cannot urge how important it is to both monitor square retention and to check for plant bugs.  Plant bugs aren’t the only cause of square loss- other stresses in the environment can cause this.  So you don’t want to spray a field where bugs aren’t the problem.  Also, plant bugs are extremely mobile, and can rapidly move in and out of fields.  Sometimes they may be present (especially adults), but not causing square loss.

    Weekly checks of upper square retention is the most efficient way to assess if plant bugs can either be ruled out as an economic concern at that time or if sweeping for the adults and nymphs is needed.  An upper square retention rate of 80% of more usually indicates that plant bugs are not present at damaging levels.  Focus on first position squares.  If upper square retention is less than 80%, you should sweep six to eight or 10 locations in the field away from the edge, looking for live adult and immature plant bugs.

    In most years in North Carolina, square retention is very high – often in the mid-90’s.  Athreshold of eight plant bugs per 100 sweeps combined with loss in square retention usually indicates that a spray is needed at that time.  Remember that when cotton is approximately one week into blooming, a five-foot black beat cloth is a more accurate sampling devise than the sweep net for plant bug, especially immatures.  I’ll blog about this sampling option in the coming weeks. This article covers what you can spray.

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