Research Report
Effects of Common Turfgrass Insecticides on Earthworms Virginia Tech Researchers: Sudan Gyawaly, Graduate Student; Curt Laub, Research Associate; and Tom Kuhar, Ph.D., Professor, Department of Entomology Research Sponsor: Virginia Turfgrass Foundation
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nsecticides are commonly applied in turfgrass systems to primarily control white grubs and to maintain a good-quality turf. The most common insecticides applied on Virginia turfgrass include imidacloprid (Merit), chlorantraniliprole (Acelepryn), clothianidin (Arena) and trichlorfon (Dylox) (see Figure 1). Additional insecticides used in Virginia include thiamethoxam (Meridian), dinotefuran (Zylam) or combination products such as clothianidinplus bifenthrin (Aloft). However, because many of these insecticides have a broad spectrum of activity and persist for a long period in soil, there is concern among people about their negative impact on nontarget organisms, including earthworms, which play an important role in the soil function of litter breakdown, soil fertility and soil microstructure. Although all insecticide products
are evaluated for their toxicity to the “red wriggler” compost worm (Eisenia fetida) in the laboratory as part of the ecotoxicological-testing requirements of the U.S. EPA for pesticide registrations (Table 1), such tests may not exactly represent the actual impact of these insecticides to other species of earthworms that typically inhabit the soil under turfgrass. The EPA Ecotoxicology Tests are only a gauge of potential negative impact on nontarget organisms.
Our research
Therefore, in 2015, we conducted a field study in Virginia to determine the effects of various turf insecticides on Lumbricus terrestis L. Although an introduced species from Europe, this is the dominant earthworm found in turfgrass in the Mid-Atlantic U.S., including Virginia (Photo 1).
Figure 1. The most widely used insecticide products on Virginia turfgrass, based on a survey we conducted in 2014 at the Virginia Tech Turfgrass Conference (Laub 2016).
14 | Virginia Turfgrass Journal May/June 2016 www.vaturf.org
Three separate field experiments were carried out during the spring, summer and fall of 2015 at the Virginia Tech Campus Golf Course in Blacksburg, VA, where the soil is a Groseclose loam, and the grass composition is a mixture of fescues, ryes, annual bluegrass and bermudagrass. Treatments used in the field experiments included several commonly used insecticide products at highlabeled application rates, plus a water control (Table 2). For spring and summer experiments, insecticides were applied on plots (5' × 5' size) arranged in a completely randomized block design, with four replications of each treatment. For spring and summer experiments, all liquid-insecticide treatments were applied as foliar sprays using a CO2 backpack sprayer. The backpack sprayer was equipped with 4,8002VS
Product
Active ingredient (AI)
Designated toxicity to red wigglers
Acelepryn 1.67SC
chlorantraniliprole
Acute toxicity
Arena 50 WDG
clothianidin
Super toxicity
Zylam (Safari) 20SG
dinotefuran
Acute toxicity
Merit 75WP
imidacloprid
Acute toxicity
Aloft GC SC
clothianidin plus bifenthrin
Extreme toxicity
Meridian 25 WG
thiamethoxam
No toxicity
Dylox 6.2 G
trichlorfon
Moderate toxicity
Table 1. List of common turf insecticide products and their EPAdesignated toxicity to earthworms, based on lab bioassays with the “red wriggler” compost worm, Eisenia fetida.