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Sod Webworm

Sod Webworms in Home Lawns

Homeowners should monitor their lawns for pests like sod webworms throughout the year—but especially during the warmer months. These caterpillars, which become active as temperatures change, can cause significant damage to turf across the United States and develop into moths.

Proper identification is key since each pest requires a unique treatment approach. This guide covers how to detect tropical sod webworms and the signs of an infestation. For sod webworms, NaturalGuard Spinosad is recommended as the most effective treatment.

What are sod webworms?

Let’s discuss tropical sod webworms (Herpetogramma Phaeopteralis Guenée), a lawn caterpillar that primarily damages turf in the southeastern U.S., as well as tropical regions like Hawaii, Puerto Rico, Guam, Jamaica and Australia.

Active mainly from May to July and again in the fall, they can be year-round pests in the southernmost areas, with a peak season from September to November. They favor newly established warm-season turfgrass in lawns, parks, commercial landscapes, sports fields and golf courses, and should not be confused with fall armyworms or black cutworms.

What does a sod webworm look like?

The adult tropical sod webworm, a small beige moth with a wingspan of 3/4 inch, initiates lawn damage. Known as a lawn moth or crambus, the female lays up to 200 yellow eggs that turn brown as they mature, typically in clusters of 10–35 on grass blades. These eggs hatch within 7–10 days into tiny juvenile caterpillars, about 1/2 inch long, that feed on the grass.

Full-grown caterpillars reach up to an inch in length and have four rows of dark spots on their abdomen. They live in individual burrows, emerging at night to feed, and can have up to five separate hatches annually.

What do sod webworms feed on?

Sod webworm larvae cause significant damage to turfgrass, primarily feeding on the blades of warm-season grasses like St. Augustine, centipede, zoysia, seashore paspalum, carpetgrass, bahia and bermuda grass. They also damage cool-season bentgrass, as noted by the University of Florida.

What are the signs of a sod webworm infestation?

The first sign of a sod webworm infestation is transparent grass blades, where juvenile caterpillars have skeletonized the blades, leaving only the vein structure. Mature caterpillars notch the blades and are mostly active at night, curling up in the thatch by day, often surrounded by moist, green fecal pellets called frass.

To detect an infestation, perform a soap flush: Mix 2 ounces of mild liquid dish detergent (like Lemon Joy, Ultra Dawn, or Ivory Clear) with 1 gallon of water. Pour this mixture within a 12-inch circle on the suspected area of your lawn. This can force the insects to the surface within five minutes, aiding identification.

For larger areas, use a diluted solution of two parts water to one part detergent to avoid turf damage. Typically, damaged turfgrass turns brown or straw-yellow, which can lead to increased weed growth as the grass canopy weakens.

How do I prevent and treat sod webworms?

Non-Chemical Control (Cultural Practices)

Healthy turfgrass is less susceptible to pests and recovers faster from damage. To help control sod webworms, consider these practices:

  • Mowing Height: Maintain the correct mowing height for your turf type. Mow St. Augustine lawns at 2–4 inches and zoysia at 0.5–2 inches, ensuring not to cut more than 1/3 of the blade at once.
  • Reduce Thatch: Proper mowing height and frequency can prevent thatch buildup.
  • Watering: Limit watering to about one inch per week, including rainfall.
  • Lighting: Turn off flood lights at night to avoid attracting moths.

Additionally, the University of Florida notes that over-fertilizing can lead to caterpillar outbreaks.

Chemical Control

To effectively manage sod webworms, sample the thatch to assess infestation levels before applying insecticides. Apply treatments like Natural Guard Spinosad late in the afternoon or early evening when caterpillars are active for the best results. Ensure to follow all label instructions for proper application and safety.

Natural Guard Spinosad – 1 Quart – Ready to Spray

Natural Guard Spinosad is an easy-to-use insect control solution that hooks up to the end of your garden hose. Available in a 1-quart bottle.

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While fertilizer doesn’t directly treat infestations, maintaining a proper fertilization schedule with products like Lawnifi® can help strengthen your lawn against stress. Lawnifi offers a subscription for seasonal fertilizer boxes, or you can purchase individual boxes as needed.

How do I control sod webworms? – Answered

To effectively control sod webworms, maintain mowing heights appropriate for your grass type—2–4 inches for St. Augustine and 0.5–2 inches for zoysia—and ensure regular mowing to prevent thatch. Water your lawn moderately, around one inch per week, and avoid using floodlights at night to deter moths.

For chemical control, assess infestation levels by checking the thatch, then apply Natural Guard Spinosad in the late afternoon or early evening, adhering to label instructions. Avoid over-fertilizing to prevent outbreaks and maintain a proper fertilization schedule to strengthen your lawn against pests.


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