Understanding mechanisms of imidacloprid failure for controlling white grubs in turfgrass

open_access
Open Access
Author:
Huling, Andrew
Graduate Program:
Agronomy
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
March 25, 2019
Committee Members:
Dr. Ben McGraw, Thesis Advisor/Co-Advisor
Dr. Ed Rajotte, Committee Member
Mary Ann Victoria Bruns, Committee Member
Keywords:
White grubs
turfgrass
imidacloprid
ELISA
Abstract:
White grubs, or larvae of scarab beetles (Coleoptera: Scarabaeidae), are the most widely distributed and destructive turf insect pests of both warm- and cool-season turfgrasses in North America. If left uncontrolled, root-feeding larvae can cause extensive damage to a turfgrass stand, impacting the plant’s ability to absorb water and nutrients, decreasing surface stability, and in the case of sports turf, increasing the probability of footing-related injuries. While cultural and biological control methods exist, chemical insecticides are favored by most turfgrass managers due to the relative effectiveness, reliability, and ease of application. Since the mid-1990s, the neonicotinoids (particularly products containing the active ingredient imidacloprid (e.g. Merit ®)) have been the most widely used white grub control products in turfgrass. However, reports of imidacloprid failures have been steadily increasing in recent years in the northeastern United States. Currently the cause of the failures is unknown, yet the managers of the affected sites have applied imidacloprid annually for a minimum of 10 years, applied controls within consistent time periods between years, and have not used other preventive insecticides for white grub control. Experiments were conducted to evaluate two factors that may contribute to imidacloprid failure for controlling white grubs, microbial degradation and thatch barriers. Microbially-mediated degradation of imidacloprid was observed in greenhouse trials. However, the relatively small amount of degradation of the active ingredient is unlikely to explain inadequate control in the field. Spatial analyses of affected sites revealed strong associations between thatch and white grub spatial patterns at most sites. In greenhouse trials, thatch did not seem to affect imidacloprid uptake. However, significantly more accumulation is occurring early in leaf tissue than root tissue/soil. The findings from this project demonstrate that multiple factors contribute to imidacloprid field efficacy and thus the degree of white grub control achieved.