Effect of aerial application parameters simulated on a spray table on insecticidal mortality of cotton aphids and stink bugs

Authors: Lopez, Juan De Dios; Latheef, Mohamed - Ab; Hoffmann, Wesley; Kirk, Ivan

Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/8/2003
Publication Date: 1/8/2003
Citation: Lopez, J., Latheef, M.A., Hoffmann, W.C., Kirk, I.W. 2003. Effect of aerial application parameters simulated on a spray table on insecticidal mortality of cotton aphids and stink bugs. Proceedings of the Beltwide Cotton Conference, January 7-10, 2003, Nashville, TN. p. 1490-1493.

Interpretive Summary: Cotton aphids and stinkbugs are important cotton pests that frequently require aerial applications of insecticide for timely control. There is very little information available on the effect of some of the major aspects of aerial application such as spray volume and concentration on insecticide efficacy. The problem is that it is very expensive to conduct these evaluations under field conditions because of the cost of operating the aircraft and the large amount of crop area that has to be treated. Therefore, we simulated aerial applications on a laboratory spray table to determine the effect of spray volume and insecticide concentration on greenhouse cotton plants infested with cotton aphids or with adult stink bugs which were confined after the plants were treated. The insecticides, acetamiprid and dicrotophos, were evaluated at 3 different concentrations and 2 and 5 gallons per acre (gpa) for cotton aphids and southern green stink bugs, respectively. Because all 3 concentrations at 5 gpa were more effective in killing both pests, these results indicated that insecticide coverage on the plants is important for these insecticides to be effective. Therefore, there may be potential for reducing the concentrations of these insecticides to save money for cost of control while using the higher spray volumes. More studies are needed with the spray table and then in the field to verify that this approach will work.

Technical 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, 0.038 and 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. 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. However, additional evaluations are needed.