Evaluation of Aerial Delivery Systems for Spray Deposition and Efficacy against Sweet Potato Whitefly on Cotton

Abstract

Sweet potato whiteflies (SWF), Bemisia argentifolii, live on the bottom surface of cotton leaves. Except crawlers, nymphal stages of the insect will not move about to contact insecticides. Aerial sprays to suppress SWF require improved application techniques designed to increase spray deposition and penetration to the lower layers of cotton canopy. Using Rotary atomizers, Winglets, and Trumpet nozzles with combination of air speed and boom heights, fenpropathrin 2.4E + acephate 90S at 0.22 + 0.56 kg active ingredient/ha, respectively, were applied at 46.7 L/ha on furrow-irrigated cotton near Maricopa, Arizona. Deposition of active ingredients and season long efficacy against SWF were determined and compared with conventional CP-03 nozzle. Neither spray deposit nor percentage coverage of active ingredients significantly varied consistently between aerial delivery systems. Rotary nozzles produced significantly smaller droplet size and higher droplet density compared to Winglets, Trumpet, and CP-03 nozzles. There was no consistent trend favoring one aerial delivery system over the other treatments against suppression of B. argentifolii on cotton. Further improvements in aerial delivery systems are needed to achieve increased control of insects that live and feed on the bottom surface of cotton leaves.

Aerial electrostatic‐charged sprays for deposition and efficacy against sweet potato whitefly (Bemisia tabaci) on cotton

“…Leaf samples for immature whiteflies were collected 3 days after sprays were applied, and sent via overnight mail to USDA Laboratory, College Station, TX, for processing. Populations of whitefly eggs and large nymphs were counted according to leaf‐plug sampling methods described earlier 13, 14…”

Quantitative impact assessment of spray coverage and pest behavior on contact pesticide performance

“…A water‐sensitive spray card (26 by 76 mm; Syngenta, Basel, Switzerland) was placed in a horizontal position immediately adjacent to each cotton plant. These yellow cards turn blue when in contact with water, and have been used mainly in research projects to obtain quantitative data on spray coverage 17, 24, 27, 35. A spray bottle (947 mL; Sprayco, Detroit, MI) containing one of the miticide solutions was held vertically above the cotton plant and water‐sensitive spray card, and the distance was varied to allow spray coverage to vary.…”

“…Many important factors affect the obtained spray coverage when pesticides are applied in field crops, including type of spray nozzle,15–17 use of adjuvants,17–21 type of carrier,22 spray volume,15–17, 23 type of spray application24, 25 and timing of pesticide applications 25, 26. Spray coverage studies involving water‐sensitive spray cards have shown that it is not uncommon, especially with aerial fixed‐wing applications, for leaf deposition to be below 1% in the lower portion of a sprayed crop canopy 24, 25, 27. Several studies have shown how weather conditions, in particular, can markedly influence the actual coverage when pesticides are applied 25, 28…”

The Performance of Insecticides – A Critical Review

“…On average, the bottom portion of the canopy received about half the spray coverage of the top portion, and only one of the nine applications provided over 10% average spray coverage in the bottom portion of the canopy. Published spray coverage studies using water sensitive spray cards have shown that it is not uncommon, especially with aerial spray applications, to obtain spray coverages below 1% [15][16][17].…”