Lawn Caterpillars

Are lawn caterpillars doing your mowing for you? Young caterpillars, or larvae, injure turfgrass by chewing notches along the edge of the leaves. This creates a ragged appearance (Figure 1) that may be hard to notice at first. Mature caterpillars eat a lot before they pupate and consume patches of turfgrass down to the crown. Because the turf looks scalped so quickly, people think that the damage occurs “overnight.” Several caterpillar species can be turfgrass pests, including the tropical sod webworm, the fall armyworm, and the striped grass looper.

Figure 1

Tropical sod webworm is most active from April through November in north Florida, but may occur year-round in south Florida. Three to four generations occur in Florida each year. Tropical sod webworm larvae feed on St. Augustinegrass, bermudagrass and zoysiagrass. Fall armyworm occurs year-round in south Florida and migrates northward each spring. This means that populations can be damaging in the spring in south Florida, but don't build up until fall in north Florida. Fall armyworm will feed on all turfgrasses, but prefers bermudagrass. Striped grass looper also occurs year-round in south Florida, and isn't a problem until fall in north Florida. Striped grass looper is primarily a pest on bahiagrass in pastures, but will readily infest other turfgrasses. Larvae of these species are active at night and will hide in a curled position near the soil surface during the day. Fall armyworm larvae may also feed during the early and later parts of the day. Green or brown pellets of frass may be visible on the soil surface, indicating that larger larvae are present. One generation of tropical sod webworm is about 6 weeks; fall armyworm and striped grass looper can develop in about 4 weeks under warm weather conditions.

The number of larvae that can cause significant damage depends on the turfgrass variety, how stressed it might be, and how tolerant the turfgrass managers or their clients are to damage. In general, most turfgrasses can tolerate the notching damage that young larvae cause, but three 1/2 inch, mature fall armyworm or striped grass looper larvae per square foot may justify a treatment. About 10 to 20 tropical sod webworm could warrant treatment. Keep in mind that large larvae may pupate quickly, which may make an insecticide application unnecessary or ineffective.  To view this entire article, please visit http://edis.ifas.ufl.edu/IN608

Figure 2.  Tropical sod webworm larv	Figure 3.    Fall armyworm larva	Figure 4.    Striped grass looper larva

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