Date of Graduation

12-2023

Document Type

Thesis

Degree Name

Master of Science in Entomology (MS)

Degree Level

Graduate

Department

Entomology and Plant Pathology

Advisor/Mentor

Thrash, Benjamin C.

Committee Member

Bateman, Nicholas R.

Second Committee Member

Lorenz, Gustav M. III

Third Committee Member

Studebaker, Glenn E.

Fourth Committee Member

Butts, Thomas R.

Keywords

Insecticides; Efficacy; Tarnished plant bug; Corn earworm

Abstract

Insecticide efficacy often varies by location and year. Many factors can influence an insecticide’s efficacy, but an often-overlooked factor is the quality of water in a carrier solution. Water quality includes many parameters, but two important ones are water hardness and pH. Research has shown that water hardness and pH can affect some pesticides. Multiple experiments were conducted to evaluate the impact of water hardness and pH on insecticide efficacy. Experiments were conducted to evaluate the impact of water hardness and pH on the efficacy and residual control of chlorantraniliprole for the control of corn earworm, Helicoverpa zea (Boddie). Leaf dip assays were conducted using 6 ng/ml concentrations of chlorantraniliprole in water samples that had three water hardness levels (11ppm, 178 ppm, 430 ppm) and three pH levels (6.5, 8.3, and 9.1). In these trials, it was observed that as water hardness and pH increased, the percent mortality decreased. Additionally, a trial was conducted in the greenhouse to determine the impact of water hardness on the residual control of chlorantraniliprole for the control of corn earworm. There were no differences observed in soft water (11ppm) and hard water (178ppm), but with very hard water (425 ppm) there was a decrease in residual after 21 days. A field trial was conducted using chlorantraniliprole, methoxyfenozide + spinetoram, emamectin benzoate, and chlorantraniliprole + lambda-cyhalothrin. No differences were observed in the field. Tarnished plant bugs, Lygus lineolaris (Palisot de Beauvois), are the most economically important insect pest in Arkansas cotton, causing major losses in yield and increasing costs for growers. Multiple experiments were conducted to determine the impact of water hardness and pH on commonly used insecticides for the control of tarnished plant control. Leaf dip assays were conducted with sulfoxaflor, acephate, thiamethoxam, and dicrotophos that were mixed with three water hardness levels (11 ppm, 178 ppm, and 430 ppm) and three pH levels (6.5, 8.0, and 9.3). A decrease in efficacy was observed for acephate as water hardness increased, however no differences were observed for the other insecticides tested regardless of water hardness or pH. A field trials were conducted to determine the impact of water hardness and pH on the efficacy of sulfoxaflor, acephate, thiamethoxam, and dicrotophos. The tarnished plant bug population was observed at 4 and 7 days after application. As pH increased dicrotophos efficacy increased 4 days after application. No other insecticides tested were impacted by water hardness of pH. Additionally, a field trial was conducted using water conditioners that were added to water with pH levels of 6.4 or 9.1 or water hardness levels of 11 ppm and 430 ppm along with dicrotophos to determine the effect of water conditioners on dicrotophos for tarnished plant bugs. No differences in efficacies were observed at 3 days but 7 days after application Diversify had an improved efficacy compared to standard water.

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