Masters Theses

Date of Award

12-2018

Degree Type

Thesis

Degree Name

Master of Science

Major

Entomology and Plant Pathology

Major Professor

Scott D. Stewart

Committee Members

Mike Buschermohle, Heather Kelly

Abstract

Aphid (Hemiptera: Aphididae) feeding may cause substantial loss of yield and grain quality by transmitting barley yellow dwarf (BYD) in wheat, Triticum aestivum L. Neonicotinoid seed treatments and foliar-applied insecticides are the two most common methods to manage aphid infestations and BYD. The overall goal for my research was to refine recommendations on the management of aphids in wheat to provide a consistent return on investment. An analysis was done across 33 insecticide efficacy trials in west Tennessee during the last eleven years to determine how neonicotinoid seed treatments and a late-winter foliar insecticide application affected aphid populations, incidence of BYD, and yield. A significant decrease in aphid populations and incidence of BYD was observed where an insecticide seed treatment, foliar insecticide, or both were used. Average wheat yields were increased by 280 – 381 kg/ha if an insecticide seed treatment or when a foliar insecticide application was made. A factorial experiment was repeated at four locations to examine how variety tolerance to BYD, a neonicotinoid seed treatment, and a foliar insecticide application affected populations of aphids, the occurrence of BYD, and yield. Similarly, experiments with various neonicotinoid seed treatments and foliar insecticide spray regimens were repeated to evaluate treatment effects on aphids, BYD, and yield. Aphid populations and BYD symptomology were consistently reduced by the use of insecticides, particularly foliar insecticides. Quantitative ELISA assays confirmed the presence of BYD in leaf tissue and was also able to detect some treatment effects on the concentration of BYD. Varieties considered tolerant to BYD had reduced symptoms of BYD, but this difference was not reflected in yield responses, and ELISA assays detected no difference between varieties in the concentration of BYD in leaf tissue. In these tests, foliar applied insecticides provided more benefit than neonicotinoid seed treatments. Collectively, my data show that insecticides should be used to manage aphids and BYD, and foliar-applied insecticides appear to provide more benefit and flexibility than insecticide seed treatments.

Comments

Portions of this document were previously published in Journal of Economic Entomology.

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