Evaluating Optimal Spray Timing, Planting Date, and Current Thresholds for Lygus lineolaris (Hemiptera: Miridae) in Virginia and North Carolina Cotton

Economically damaging infestations of Lygus lineolaris (Palisot de Beauvois) (Hemiptera: Miridae), the tarnished plant bug, have been increasing in North Carolina and Virginia cotton since 2009. We conducted experiments to compare prophylactically timed sprays based on cotton phenology and current action thresholds based on sweep net and drop cloth sampling. In the second year of the study, we included planting date as a factor, with early and late-planted cotton. We found L. lineolaris nymph densities were reduced by at least 60% in North Carolina and 74% in Virginia in threshold plots when compared with the untreated control. Protecting the crop from first square through the fourth week of bloom afforded at least 30% control across planting dates in Virginia and at least 40% control in North Carolina. Economic returns were two to three times greater in early-planted cotton than in late-planted cotton. Treating cotton at action threshold or using prophylactic sprays from first square until the sixth week of bloom in early-planted cotton yielded over $500/ha in net returns in both North Carolina and Virginia. This study supports previous research that shows controlling L. lineolaris infestations during squaring and early weeks of flowering is critical for maximizing yield potential. Our findings also suggest that prebloom and bloom thresholds based on adult and nymphal density devised in the Mid-South may need revision in North Carolina and Virginia.