Sod Webworms, Armyworms, and Grubs in St. Augustine

Sod webworms

Sod webworms are the larvae of small, dull tan moths. You'll often notice the moths first: they flutter up in short, zigzag flights when you walk across the lawn around dusk. The larvae hide in the thatch during the day and feed at night.

Signs

• Early on, small yellowish spots that are easy to mistake for dog spots.
• Later, blades that are chewed, notched, or eaten down, and patches that thin out and merge in dry weather.
• Heavy bird activity, since birds feed on the larvae.

Fall armyworms

Fall armyworms are caterpillars that move through a lawn in large numbers, usually in late summer and fall, often after rain. They feed during the day and can strip an area down to brown stubble in a couple of days. Look for green to brown caterpillars with stripes along the body and a light, upside-down "Y" on the head.

The good news: armyworms eat the leaves, not the runners, so a healthy St. Augustine lawn usually grows back once they're gone. The damage looks worse than it is if you act quickly.

Grubs

Grubs are the white, C-shaped larvae of beetles. They live in the soil and chew off roots, so damaged grass wilts, browns, and can be peeled back like loose carpet. Animals digging in the lawn can also be a sign. Grubs aren't a common problem in most St. Augustine lawns, so dig and confirm before you treat.

How to check

Soap flush (webworms and armyworms)

1. Mix about 1 ounce of dish soap into a gallon of water.
2. Pour it evenly over about a square yard at the edge of the damaged area.
3. Watch for 5 to 10 minutes. The soap irritates caterpillars and drives them to the surface where you can count them.

Dig test (grubs)

Cut three sides of a square-foot section of turf at the edge of the damage, a few inches deep, and fold it back. Count the C-shaped larvae in the soil and roots. A few is normal; a lot in one spot, along with turf that lifts easily, points to grubs.

When to treat

• Caterpillars: treat when you confirm active larvae and see fresh feeding. Insecticides work best on young larvae, so act early. Apply late in the day, when caterpillars are active, using a product labeled for lawn caterpillars on St. Augustine.
• Grubs: only treat when you've found them in numbers. Follow the label for timing, since some grub products work as prevention and others as a cure.
• Prevention: the Turf Method program's preventative insect applications in April, June, and August cover many of these pests along with chinch bugs. In my program that's Spectracide Triazicide. Check the product label for the pests it lists.

After any insect damage, water deeply and give the lawn a few weeks. St. Augustine recovers from the runners.