**Sod Webworms** (*Crambus* and *Pediasia* species) are the larvae of small, tan-colored lawn moths, and they are a serious, widespread pest of **turfgrass** (lawns, golf courses, and sod farms). The conflict is aesthetic and economic: the caterpillars feed by **chewing grass blades** near the soil surface, causing thin spots and large, unsightly **brown patches** of dead grass. In severe cases, they can completely destroy large areas of turf, requiring expensive replacement.
Taxonomy and Classification
Sod Webworms belong to the order Lepidoptera (Moths and Butterflies). They undergo complete metamorphosis. The larvae are nocturnal feeders, hiding during the day in silken tunnels or burrows near the soil line, often mixed with grass clippings and feces (the “web” that gives them their name).
Physical Description
The destructive larvae are $3/4$ to $1$ inch long.
- **Adult Moth (Key ID):** Small, buff, or tan moth that flies erratically in a zig-zag pattern just above the grass when disturbed (the “lawn moth”). They often rest on walls with their wings folded tightly around their bodies.
- **Larva (Key ID):** Grayish-brown, slightly spotted caterpillar with a dark head. Found curled up in the upper thatch layer.
- **Damage Sign (Key ID):**
- **Brown Patches:** Irregular, yellowish-brown dead patches in the lawn.
- **Silken Webs:** Small, tubular silken webs or tunnels found in the thatch, often with green pellets of frass (feces) visible.
- **Nocturnal Activity:** Birds feeding heavily on the turf in the early morning can indicate high webworm populations.
- **Conflict:** Turfgrass destruction and aesthetic loss.
Distribution and Habitat
Sod Webworms are widespread throughout North America. Their habitat is the thatch layer of turfgrass, where they feed on the grass blades at night, particularly favoring blue-grass and perennial ryegrass.
Behavior and Conflict
The conflict is dominated by the hidden, continuous feeding.
- **Damage Timing:** The most severe damage typically occurs during mid-to-late summer when the lawn is already stressed by heat and drought.
- **Control Difficulty:** The larvae hide during the day, making contact insecticide application less effective, and their presence is often not noticed until significant brown patches appear.
- **Multiple Generations:** They can have two to four generations per year, requiring repeated monitoring and control efforts.
Management and Prevention
Control is integrated pest management (IPM), with precise monitoring and well-timed treatment.
- **Drench Test:** Use a soap-drench test (mix $1$ tablespoon of dish soap in $1$ gallon of water and pour over $1$ square foot) to bring the webworms to the surface for counting. Treatment is usually warranted if $15$ or more caterpillars surface per square yard.
- Apply the biological insecticide *Bacillus thuringiensis* (Bt) or entomopathogenic nematodes (*Steinernema carpocapsae*) in the evening when the larvae are actively feeding.
- Apply granular or liquid insecticides (containing pyrethrins or carbamates) in the late afternoon/early evening and avoid watering immediately afterward, to ensure the chemical reaches the feeding larvae.
Conservation and Research
Sod Webworms are managed as high-priority turfgrass pests. Research focuses on improving monitoring techniques, developing resistant grass cultivars, and enhancing the efficacy of biological control agents against nocturnal feeders.