Earthworm castings
Lumbricidae (e.g., Lumbricus terrestris, Aporrectodea spp.)
Soil-dwelling earthworms are beneficial below ground but deposit muddy surface mounds (casts) that disrupt closely mown, high-value turf.
Identification
Earthworm castings are small mounds of muddy, excreted soil deposited at burrow entrances on the turf surface, not a pest in themselves. They are recognized as gritty, granular soil piles that smear into muddy slicks when crushed by mowers, tires, or foot traffic, most conspicuous on closely mowed greens, tees, and fairways. The night crawler (Lumbricus terrestris) is the chief casting-forming species.
Symptoms & Damage
Numerous soil mounds that disrupt ball roll, dull and damage mower bedknives and reels, and, when smeared, smother grass and reduce photosynthesis, creating muddy, uneven, weak-spotted surfaces. The turf itself is not fed upon — the injury is mechanical and aesthetic.
Biology
Earthworms are soil-dwelling annelids — not insects — that ingest soil and organic matter such as decaying turf tissue and deposit the processed material as surface casts. Casting activity tracks soil moisture and temperature rather than a pest life cycle, intensifying when soils are cool and saturated. Earthworms are long-lived and active in the upper soil whenever conditions are favorable.
Occurrence & Spread
Casting is heaviest in early spring and again in fall when soils are wet and workable, and is worst on fine-textured clay or silt soils. It is primarily a playability and maintenance nuisance on golf courses and sports fields rather than a turf-health problem.
Favorable Conditions
Cool, moist soils with abundant organic matter or thatch and near-neutral pH. Surface casting slows in hot, dry conditions and during drought.
Cultural Management
Earthworms are beneficial soil engineers that improve aeration, drainage, and thatch breakdown, so the goal is to manage the nuisance, not eliminate them. Topdress with sand to make casts easier to break up and disperse, improve drainage and regulate soil moisture, and switch to light dragging/brushing to disperse casts; raising soil pH where appropriate can reduce activity. No insecticides are registered or recommended to target earthworms.
Further Reading
University extension resources — open in a new tab.
Related Reports
No published reports yet for this pest.
Reports will appear here as they are peer-reviewed and published.