Toxicity of Pesticides to Earthworms (Oligochaeta: Lumbricidae) and Effect on Thatch Degradation in Kentucky Bluegrass Turf

Abstract

Earthworms are important, beneficial invertebrates in turfgrass, where their burrowing and feeding activity enhances soil structure and fertility and incorporates thatch and other plant residues into the soil. The comparative toxicity of 17 commonly used turfgrass pesticides and recovery of earthworm populations following exposure were studied for 2 yr in Kentucky bluegrass turf. A single application of the fungicide benomyl or the insecticides ethoprop, carbaryl, or bendiocarb at labeled rates reduced earthworm populations by 60-99%, with significant effects lasting for at least 20 wk. These compounds also significantly reduced the rate at which earthworms incorporated mineral soil into buried pieces of thatch. Other insecticides, specifically diazinon, isofenphos, trichlorfon, chlorpyrifos. and isazophos caused less severe, but significant earthworm mortality in some tests. None of the herbicides tested significantly affected earthworm populations. The abundance of Cryptostigmata, Collembola, and ants also was drastically reduced by some treatments. Preservation of earthworms and other beneficial soil invertebrates may be critical to long-term stability of the turfgrass ecosystem.