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Publication #ENY-352

Lawn Caterpillars1

Eileen A. Buss and Robert Meagher2

Have you ever seen grass that was so infested with caterpillars that it looked like the grass was scalped and the ground was moving? Have you had to skim the caterpillars or frass out of a swimming pool? 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.”

Figure 1. 

Caterpillar damage to St. Augustinegrass.


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Identification

The species that most commonly live in and damage Florida's warm season turfgrasses include the tropical sod webworm (Herpetogramma phaeopteralis), fall armyworm (Spodoptera frugiperda), striped grass loopers (Mocis spp.), and the fiery skipper (Hylephila phyleus).

Tropical sod webworm - TSW caterpillars (Figure 2) are gray-green, have brown spots on each segment, and are the smallest caterpillars of the species listed (Figure 1). Mature larvae can be ¾ to 1 inch long, and they pupate in the thatch or on the soil surface. Adults (Figure 3) are small, tan to gray moths with a wingspan of ¾ to 1 inch. They do not cause damage. Moths hide in shrubs and other sheltered areas during the day, and fly low when disturbed. Females lay clusters of 6-15 white eggs on grass blades at night. Eggs hatch within 7 days.

Fall armyworm - FAW caterpillars (Figure 4) can be green or brown, and mature larvae are 1½ inches long with four pairs of fleshy prolegs on the abdomen. As larvae grow, light stripes appear along the length of the body and dark spots appear on the top of each segment. FAW have an inverted light-colored 'Y' on the front of their head. They pupate in the soil. The adults (Figure 5) are larger, with a wingspan of nearly 1½ inches. Females are almost all gray, but males are shaded gray and brown and have white spots near the center of the wing and near the tip. FAW eggs are laid in clusters of 50-150 along grass blades or on non-plant surfaces. Eggs (Figure 6) are grayish in color, and are coated with moth scales.

Striped grass loopers - SGL (Figure 7) have a longer and thinner body and “loop” like inchworms when crawling. They only have two pairs of fleshy prolegs. Their color ranges from cream to black, there is a light-colored narrow stripe down their backs, and many stripes on their heads. SGL pupate on tall pieces of grass or small shrubs. Adults (Figure 8) are the largest of the group, with a wingspan of 1½ inches (Figure 8). Wings are tan to yellowish-brown in color with vertical lines and round spots. Eggs are laid singly on grass blades.

Fiery skipper - These caterpillars have a very distinctive “neck” that is constricted behind the black head (Figure 9). The body looks plump, is covered with tiny bristles, and the skin surface appears pebbled. Young caterpillars are a pale yellow-green color, but mature larvae reach up to 1 inch long, are yellow-brown to gray-brown, and have a faint stripe down the middle of the back. Pupation occurs in the thatch, at least partially enclosed in a cocoon of loosely webbed plant debris. Adults are stout yellowish butterflies, marked with orange and brown (see the website: http://www.ipm.ucdavis.edu/TOOLS/TURF/PESTS/inskipper.html). Their eyes are large and dark, and the wingspan is about 1 inch. Eggs are laid singly on the undersides of leaf blades.

Figure 2. 

Tropical sod webworm larva.


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Figure 3. 

Tropical sod webworm adult.


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Figure 4. 

Fall armyworm larva.


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Figure 5. 

Fall armyworm adult male.


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Figure 6. 

Fall armyworm egg mass.


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Figure 7. 

Striped grass looper larva.


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Figure 8. 

Striped grass looper adult.


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Figure 9. 

Fiery skipper larva.


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Biology

In southern Florida, caterpillar populations may be active year-round. However, moths from the south may fly into north Florida during late spring, and reinvade. Populations build up over the summer and may cause significant damage by late summer or fall. The adults (moths) of all three species are active from dusk till just after dawn. 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.

One generation develops in about 6 weeks. Frost tends to reduce tropical caterpillar populations over the winter or possibly induce them to pupate. 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. Fall armyworm and striped grass looper can develop in about 4 weeks under warm weather conditions. 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 can develop in about 4 weeks under warm weather conditions.

Management

Monitoring

It is fairly easy to tell the difference between caterpillar damage and other turf problems, but damage may not be obvious until larvae are near pupation. Young caterpillars scrape or notch along the edge of the grass blades. Older larvae can consume most of the grass blade, and patches of brown grass mixed with a couple of green grass blades develop. The presence of bright green frass (insect feces) somewhat silked together in the thatch is a give-away for tropical sod webworm caterpillars. Caterpillars don't leave water marks, spores, mushrooms, spots or streaks on the grass blades, tunnels, or affect the roots. Scalping or mowing too low by a lawn mower will likely be in a straight line at a uniform height. Insects are't usually that neat.

To find larvae, part the grass in suspect areas and look for chewed leaves, silken webs, frass, and larvae. A soap flush generally involves mixing 1-2 gallons of water with 1-2 tablespoons of liquid dish soap, and pouring it over the infested (but not dead) turf. The caterpillars emerge quickly, can be collected, placed into a container, and then identified. If nothing emerges, examine several other areas.

The number of caterpillars that can cause significant damage depends on the turfgrass species and variety, if it is also affected by other biotic or abiotic stresses, 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 15 tropical sod webworm could warrant treatment. Keep in mind that large larvae may pupate quickly, which may make an insecticide application unnecessary or ineffective.

A commercially available sex pheromone lure can be used to monitor fall armyworm. The pheromone for grass loopers is not yet available.

Cultural Control

Cultural practices can influence turfgrass susceptibility to these caterpillar species. Turf can recover from damage if properly irrigated and kept healthy. Drought or low mowing heights may reduce or prevent grass recovery. Because many eggs are laid on grass blades, removing and destroying cuttings after mowing might reduce infestations.

Application of water-soluble, inorganic nitrogen fertilizers causes rapid leaf growth, and increases the chance of caterpillar problems. Female moths that are ready to lay eggs are attracted to the succulent leaves. Responsible use of slow-release fertilizers may reduce turfgrass susceptibility.

Many insects, including lawn caterpillars, live in thatch, which is a layer of accumulated dead plant roots, stems, rhizomes, and stolons between the live plant and soil. Over-watering or over-fertilization can cause turf to develop a thick thatch layer. Excessive thatch should be mechanically removed (vertical mowing, power raking, etc.) to minimize insect habitat and minimize binding of pesticides to organic matter.

Biological Control

Ants, ground beetles, rove beetles and spiders are predators of caterpillars in lawns. One parasitic wasp, Horogenes sp., attacks tropical sod webworm larvae, and other wasp species attack fall armyworm (Aleiodes laphygmae and Cotesia marginiventris). Parasitic flies attack striped grass looper larvae (Sarcodexia sternodontis and Chetogena sp.). Preventive pesticide use in lawns can reduce natural enemy populations and reduce their ability to naturally minimize pest populations.

Microbial control products (e.g., fungi, viruses) may also be commercially available to manage caterpillars in environmentally sensitive areas.

Chemical Control

Control should only be directed against the feeding larvae. Applications should be timed against young larvae, for greater efficacy. The smaller caterpillars are easier to kill with “softer” products like those containing Bacillus thuringiensis (B.t.k.), chlorantraniliprole (Acelepryn™), dimilin (Dimilin®), halofenozide (Mach 2™) or spinosad (Conserve®). More broad-spectrum products, like pyrethroids, may be needed to control mature larvae.

Spot treatments may be applied when infestations are first detected and the damaged area is small. A treatment might be most effective if applied in the early evening when larvae begin feeding. Examples of products that can be used are in Table 1. A reapplication may be needed if moths continue to fly in, lay eggs, and new larvae hatch out while the product residual is breaking down.

If moths fly out of the turf or when shrubs are disturbed, realize that adults may be laying eggs and another generation is getting started. Avoid treating moths - adults are not the target because they don't cause damage and are unlikely to receive a lethal dose if the grass is treated. Trying to spray into the air to kill moths flying out will also create unnecessary insecticide drift and increases the risk of harming pets or people.

Note: Only a few formulations of recommended insecticides are listed in the table to serve as examples. Others may be available. Read the label carefully for use directions, application techniques, irrigation requirements, and precautions.

References

Brandenburg, R. L. and M. G. Villani. 1995. Handbook of Turfgrass Insect Pests. Entomological Society of America, Lanham, MD.

Niemczyk, H. D. and D. J. Shetlar. 2000. Destructive Turf Insects, 2nd ed. H.D.N. Books, Wooster, OH.

Potter, D. A. 1998. Destructive Turfgrass Insects: Biology, Diagnosis, and Control. Ann Arbor Press, Chelsea, MI.

Tables

Table 1. 

Active Ingredient

Chemical

Retail/homeowner product examples

Professional Product

Acephate

Organophosphate

--

  • Acephate Pro 75

  • Orthene Turf, Tree & Ornamental Spray

Bacillus thuringiensis subspecies kurstaki

Microbial

  • Green Light Dipel Dust

  • Safer Caterpillar Killer

  • Dipel

  • Thuricide

Bifenthrin

Pyrethroid

  • Ortho Home Defense MAX Granules

  • Southern Ag Lawnstar Bifenthrin Insecticide G

  • Onyx

  • Talstar EZ, P, PL,S

Carbaryl

Carbamate

  • Sevin

  • Sevin SL

  • Sevin 80 WSP

Chlorantraniliprole

Anthranilic diamide

--

  • Acelepryn

Clothianidin

Neonicotinoid

  • Green Light Grub Control with Arena

  • Arena

Cyfluthrin

Pyrethroid

  • Bayer Advanced Rose & Flower Insect Killer

  • Bayer Advanced Power Force Multi-insect Killer

  • Schultz Lawn & Garden Insect Killer

  • Tempo SC Ultra

Deltamethrin

Pyrethroid

  • Southern Ag Mole Cricket & Chinch Bug Lawn Insect Control

  • DeltaGard G

  • DeltaGard T&O SC

Diflubenzuron

Insect growth regulator

--

  • Dimilin 2L (sod farm only)

Halofenozide

Diacylhydrazines

  • Hi-Yield Kill-A-Grub

  • Southern Ag Mach 2 Grub Control

  • Mach 2 G

Indoxacarb

Oxadiazine

--

  • Provaunt

Lambda-cyhalothrin

Pyrethroid

  • Spectracide Triazicide Once & Done Insect Killer

  • Demand CS

  • Scimitar GS

Permethrin

Pyrethroid

  • Bonide Eight Liquid

  • Green Light Conquest Insecticide

  • Hi-Yield Indoor/Outdoor Broad Use Insecticide

  • Ortho Bug-B-Gon Max Garden Insect Dust

  • Astro

  • Ambush

  • Permethrin Pro Termite-Turf Ornamental

Spinosad

Spinosyns

  • Bulls-Eye Bioinsecticide

  • SpinTor, Success, Tracer

Trichlorfon

Organophosphate

  • Bayer Advanced Lawn 24-hour Grub Control

  • Dylox, Proxol

Footnotes

1.

This document is ENY-352 (IN608), one of a series of the Department of Entomology and Nematology, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Date first published: April 2006; revised October 2010. Please visit the EDIS Website at http://edis.ifas.ufl.edu.

2.

Eileen A. Buss, assistant professor, Department of Entomology and Nematology, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, and Robert Meagher, USDA-CMAVE, Gainesville, 32611.


The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.