Turfgrass Caterpillars

Species & Identification

Several species of caterpillars can damage turfgrass. Cutworms, sod webworms, and fall armyworm are three major groups of caterpillar pests in South Carolina. Identification of caterpillar species based on moth (i.e., adults) appearance can be difficult because many species look similar. Therefore, identification based on adults is not recommended.

Caterpillars can be identified to groups based on general appearances. Cutworms are gray green in color with two rows of black spots on the back. They often roll into a ball when picked up. Sod webworms are green to tan in color with dark brown heads and dark spots along the back. When picked up, temperate sod webworms will roll up into balls, whereas tropical sod webworms thrash about. Fall armyworm can appear green to black in color and have a characteristic Y-shaped white mark across the middle of its head.

Damage & Symptoms

All caterpillar species feed on the leaf blades of turfgrass. Smaller caterpillars remove pieces of leaf tissues, skeletonize leaf blades, and cause a ragged appearance. Larger caterpillars may consume an entire leaf blade. When infestation is severe, a large patch of turf may appear thinned and ragged. Damage is not permanent; the turf will recover once the caterpillars have been removed and proper growing or maintenance practices are followed.

Cutworms seem to prefer closely mown turfgrass (e.g., tees and greens). They emerge from soil burrows at night to feed near those burrows, creating circular thinned spots. While cutworms sometimes use aerification holes as burrows, studies suggest that aerified turf does not attract more cutworms.

Sod webworm damage can thin canopies of closely mown turfgrass or give a ragged appearance to taller turfgrass. Feeding damage tends to appear as thinned, discolored patches in the turf stand.

A group of fall armyworms can rapidly defoliate large areas of turfgrass. Their feeding damage typically radiates from vertical objects (like fences, walls, or tree lines) where moths deposit eggs. Hatchlings then move downward, causing the radiating damage.

Life Cycle

Caterpillars are the immature stage of moths. Female moths deposit eggs on objects or grass blades, and hatchlings begin feeding immediately. Damage becomes more severe as caterpillars grow. Mature caterpillars pupate in the soil and emerge as moths after several weeks. Each generation is completed in two to four weeks.

Cutworms typically have five to six generations per year. Sod webworms have three to four generations from late spring through fall. Fall armyworm populations move northward from Florida and Texas each year. They are most numerous in August but may start arriving as early as May, with four to five generations per year. All fall armyworms in South Carolina are killed after the first frost.

Scouting

Soapy water flushes are effective for caterpillar scouting. Increased bird activity may also indicate an infestation. Sod webworms hide in thatch and may be seen by parting the turf canopy, while fall armyworms and their egg masses—covered in fuzzy scales—can often be spotted on vertical surfaces.

Cultural Control

Clippings from infested turf should be removed to discard eggs attached to the blades. Overseeding with endophyte-enriched cool-season turfgrasses (like fescue and perennial ryegrass) can help defend against sod webworms in the fall and winter. While many pest species show a preference for certain turfgrasses, no species is completely resistant. Maintain proper fertilization and irrigation to help the turf recover.

Biological Control

Native natural enemies such as ground beetles, ants, paper wasps, and parasitic wasps attack all caterpillar species. These organisms are not available for purchase, so the best approach is to protect them by avoiding broad-spectrum insecticides like carbamates, organophosphates, and pyrethroids.

Products containing Bacillus thuringiensis (subspecies aizawai or kurstaki) are widely available, as are formulations with other biological control agents. These biopesticides should be applied against small caterpillars and may require repeated applications.

Chemical Control

Insecticide applications should target young caterpillars for best efficacy. There are no treatment thresholds for cutworms or fall armyworms; control measures should be taken as soon as caterpillars are detected. Sod webworms have treatment thresholds of 20–30 caterpillars per square yard in high‑cut turfgrass and 5–15 in closely mown turfgrass.

Since caterpillars are exposed to insecticide residues via ingestion or contact, irrigation should be withheld for at least overnight or applications avoided if rain is forecast to prevent washing off the residue.

Selected Insecticides for Caterpillar Control

Here are some selected insecticides:

• Bacillus thuringiensis (Bt): Effective against young caterpillars in the early stages of infestation.
• Spinosad: Provides good control, particularly on high-value turf areas.
• Pyrethroids: Broad-spectrum insecticides effective for knockdown control, but use with caution to protect beneficial insects.
• Insect Growth Regulators (IGRs): Target young caterpillars to prevent them from developing into adults.