There are several species of caterpillars called sod webworms that can be highly destructive pests. The damaging stage is the caterpillar or larval stage. Typical sod webworm caterpillars have a dark head. Their bodies are light brown or gray with dark spotting. Webworm-infested thatch has silken tunnels produced by the caterpillars. During the day, they hide within these webbed tubes, and at night they move out a short distance to feed. Sod webworms are typically about 2.5 cm (1inch) long when full grown.
The moths are small (1/2 inch long) and whitish-gray. They clasp or roll their wings close to their bodies when resting and have mouthparts projecting forward from the head like a snout. The moths are usually noticed when flushed out by a lawn mower or people walking. When disturbed, they fly in a jerky zig zag manner and quickly return to the grass to hide. Around dusk, they may be seen flying a few feet above the grass and dropping their eggs.
The number of lifecycles per year varies among the different species of sod webworm, but in general there are 2 to 3 life cycles a year.
The webworms overwinter as young larvae a few centimeters below the soil line among the roots of weeds and grasses in silk-lined tubes. During early spring the larvae feed on the upper root systems, stems, and blades of grass. They build protective silken webs, usually on steep slopes and in sunny areas, where they feed and develop. In early May, they pupate in underground cocoons made of silk, bits of plants, and soil. About two weeks later, adults emerge. Larvae feed nocturnally for 3 to 4 weeks. Beginning in late May or June, moth flights may occur until October. The moths, erratic and weak flyers, live only a few days and feed solely on dew. They are active at dusk, resting near the ground in the grass during the day.
The eggs, which are deposited indiscriminately over the grass, hatch in 7 to 10 days. Young larvae immediately begin to feed and construct their silken tunnels.
The most severe damage occurs in July and August when the grass is not growing rapidly. During this hot weather, the larvae feed at night or on cloudy days.
Most sod webworms complete 2 or 3 generations each year, with approximately 6 to 8 weeks elapsing between egg deposition and adult emergence.
The first generation adults appear in June and the second-generation adults in late July and August. Historically, the second, generation larvae have caused the greatest amount of damage.
Damage generally becomes evident in late summer. The sod webworms feed on the upper root systems, stems, and blades of grass. The sod webworm feeding exposes the crown of the grass to the hot sun; thus, the injury is much worse during hot, dry weather. As the caterpillar grows, it can damage an area of lawn about the size of a softball. If the infestation is severe, the spots may develop into much larger areas.
First and foremost, it is important to ensure adequate fertility, a balanced soil pH and low soil compaction to encourage a robust lawn that will be able to tolerate some insect feeding.
Make sure you are mowing and watering properly as well.
There are a variety of control strategies, including the use of predatory nematodes, as well as conventional insect controls.
Overseeding with a mix of entophytic perennial ryegrass is another excellent strategy to prevent future sod webworm damage. The entophytic perennial ryegrass contains a naturally occurring fungi that deters insect feeding on the leaves.
If you think you have a sod webworm problem, contact your local Nutri-Lawn and we will come out and diagnose the problem and recommend the best control strategy for your situation.