ABSTRACT

A spray table calibrated for spray rates of 2 and 5 gallons/acre (gpa) with 2 different nozzles was used to simulate aerial applications on cotton to determine effects on insecticidal mortality of cotton aphids, Aphis gossypii Glover, and southern green stink bugs, Nezara viridula (L.). Spray droplet characteristics for both spray rates were similar except for the number of droplets/cm². Acetamiprid (Intruder®) and dicrotophos (Bidrin®) at various active ingredient (ai) concentrations were evaluated for aphids and southern green stink bugs, respectively. Acetamiprid at 0.025, 0.038and 0.05 lb ai/acre (ai/ac) at 5 gpa significantly reduced aphid numbers per leaf compared to control by 3 days after treatment (DAT) and to essentially zero by 5, 7 and 14 DAT which indicates good residual activity. At 2 gpa, only the 0.038 and 0.05 ai rates significantly reduced aphid numbers by 3 DAT, but the decrease was significantly less than for all 3 ai rates at 5 gpa. A delayed effect for aphid control at 2 gpa was evident because by 5 DAT and thereafter, there were no significant differences in numbers of aphids/leaf at all rates for both 2 and 5 gpa; however, numbers were not essentially zero in the 2 gpa. Dicrotophos at 0.125, 0.25 and 0.375 lb ai/ac with exposures starting 1 DAT significantly reduced the percent of stink bugs alive compared to control by 2, 3 and 4 DAT for all ai rates at 5 gpa and all percentages alive were statistically equal except for 0.125 lb ai/ac at 2 DAT. For 2 gpa at 2 DAT, only the 0.375 ai rate significantly reduced the percentage alive and this was the only rate that reduced numbers to those not significantly different from all ai concentrations at 5 gpa. These results show that for both insecticides and pests, coverage is important for efficacy and that there is potential for using lower ai concentrations at 5 gpa to reduce control costs, but additional evaluations are needed.