Virginia Turfgrass Journal - May / June 2016

Page 14

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


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

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


Active ingredient (AI)

Designated toxicity to red wigglers

Acelepryn 1.67SC


Acute toxicity

Arena 50 WDG


Super toxicity

Zylam (Safari) 20SG


Acute toxicity

Merit 75WP


Acute toxicity

Aloft GC SC

clothianidin plus bifenthrin

Extreme toxicity

Meridian 25 WG


No toxicity

Dylox 6.2 G


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.

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