Reevaluating Lygus lineolaris Thresholds and Spray Times in North Carolina Coastal Plains Cotton

Action thresholds for tarnished plant bug (Lygus lineolaris) have never been systematically evaluated in the Southeast. Current North Carolina treatment recommendations are based on those from the Mid-South.  Given the increase in plant bug pressure in the last five years, a reevaluation of those thresholds would be prudent. Reevaluation of previous thresholds in the Mid-South showed that their 8 plant bugs per 100 sweeps threshold was too conservative (Musser et al. 2009). North Carolina growers will benefit greatly by having a target threshold for plant bug in cotton. These thresholds will be more relevant to nearby Southeastern states and target plant bug at the most effective time.

This paper will present two experiments addressing two different issues. The first addressed treatment thresholds. There will be seven treatments: pre-bloom, early bloom, late bloom, pre-boll, low plant bug, high plant bug, and an untreated control. The main purpose of these treatments will be to create differential populations at different locations during different times of cotton phenology to evaluate thresholds. A secondary goal of having these treatments is to isolate the time when cotton in NC is most susceptible to plant bug injury.

The second experiment we compared the efficacy of selected insecticides registered for TPB in North Carolina: Strafer, Belay, Admire Pro, Centric, Transform, Orthene, and Diamond. We tested them using the recommendations from the Mid-South that sequential sprays are most effective in lowering populations of plant bug nymphs below economic thresholds (Gore et al. 2015). The methods listed below will not test the hypotheses of insecticide susceptibility across space or time, but will serve as more detailed preliminary data to better target future experiments and, hopefully, improve insecticide control in the short term. Data will be presented with appropriate statistical comparisons.