Article by Jack Bacheler, NCSU Extension Entomologist
Thrips ”Season” over for most: Thrips beat some folks up (cotton seedlings, that is) pretty bad this year, with most damage hitting producers who used a seed treatment but didn’t respond quickly enough when the seed treatment residual ran out early after only about 2 or 2½ weeks of residual activity following a stretch of warm very dry weather. This weather pattern served to dry down thrips weed hosts surrounding cotton fields, resulting in large incoming adult flights that were on the late side but into generally late cotton. Add in some herbicide injury and heavy rainfall, and many cotton fields got off to a rough start. It’s nice to see our present good moisture conditions and warm weather – at least for many.
Chill: With the thrips season over (or almost past) for most NC cotton growers, we often have a period when insects leave us alone. Hopefully that will be the case this year. We have only had a few calls about spider mites and plant bugs – so far nothing yet treatable has been brought to our attention. Judging from a random sampling of cotton field drive-bys, weed management looks like significant challenge for many
Big year for plant bugs? Based on a few corn field assessments and some ditch bank sweepings, we seem to have more that our usual level of plant bugs so far this season. A large eastern NC consultant (not overweigh – just many grower clients), notified us with the same observation on corn. Many wild flowering weeds are good early hosts for plant bugs. Once these hosts and corn silks dry down, adult plant bug movement into cotton can materialize quickly.
Square retention assessments: With some cotton fields now squaring, square retention monitoring should be underway in those fields. 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. If upper square retention is less than 80%, we recommend sweeping 6 to 8 or 10 locations in the field away from the edge, looking for live adult and immature plant bugs (see Cotton Information, page 126-127 for more details). In most years in North Carolina, square retention is very high – often in the mid-90’s. A threshold of 8 or so plant bugs per 100 sweeps usually indicates that a spray is needed at that time (see related North Carolina Field Crop Blog article by Dominic Reisig). Remember that when cotton is approximately 1 week into blooming, a 5-foot black beat cloth is a more accurate sampling devise than the sweep net for plant bug, especially immatures. We’ll discuss this sampling option in the coming weeks.
Call or email us: It’ll be interesting to find out what we all see in the way of cotton aphids, spider mites and plant bugs in the coming weeks. We’ll try to keep you posted. Please feel free to send us your observations (firstname.lastname@example.org or 919-333-0766).
Cotton/Soybean Scouting Schools: Beginning with the next issue of Pest News, we will begin posting upcoming cotton/soybean scouting schools. Indoor and outdoor training will be offered for both crops. Presently we plan to have schools in Onslow, Greene and Bertie counties during the week of July 15-18. The details of these, and hopefully other schools, will follow.