Sod webworms in bluegrass |

Sod webworms in bluegrass

Richard Snell
Barton County Extension Agent

Out of sight – out of mind, that’s how I usually operate. We don’t have much bluegrass in our area, so after several calls on brown looking bluegrass lately that didn’t have grubs, I am suspecting we have some bluegrass sod webworm activity.

However, I didn’t pick up on this right away because it has been several years since I personally have seen it.

I grew bluegrass in my lawn when I used to live in the northeast corner of the state. As Tom Thole used to say it has that wheat green color. However in this part of the state I don’t recommend it because it requires more maintenance and has more problems than fescue.

The Bluegrass Sod Webworm is one of the most destructive pests of turf in Kansas. Infestations often damage bluegrass or mixtures of bluegrass and tall fescue.

This webworm also attacks bentgrass greens on golf courses, can sometimes be of concern in plantings of pure tall fescue, and has been reported occasionally on bermuda grass. In most instances, bermuda grass develops vigorously enough that serious problems are rare.

Sod webworms are the caterpillars of lawn moths. 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 zigzag 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. In a few days, these eggs and others laid on the lower parts of the grass stems hatch into small caterpillars. It is the caterpillar that damages the grass.

The caterpillars generally have dark heads and rows of light-brown spots arranged in rings around the greenish-gray bodies. They live near the soil surface in silken shelters covered with bits of grass, essentially webbing the thatch into a mat. The larvae clip off grass blades close to the round and pull them back into their silken ‘runways.’ After several weeks of feeding, they reach maturity (now about 3/4 inch long), change into pupae (the resting stage), and soon emerge as moths. Two generations occur each year. 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 in Kansas.

The close clipping of grass blades by the sod webworm larvae does not kill the grass directly but exposes the crown to the hot, beating 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.

If lawn moths are abundant, watch for signs of caterpillars feeding during the next 7 to 14 days. Realize though, that an abundance of moths does not automatically mean that damaging larval populations will necessarily develop. Also indicative of a sod-webworm infestation are large numbers of birds, particularly starlings, pecking holes in the lawn looking for caterpillars.

One method used to drive the webworm larvae (and many other above, ground feeders) to the surface for counting involves the application of detergent or pyrethrum solution to the lawn. Mix 1 quart of water and one tablespoon of powdered detergent (Tide or a similar product), then sprinkle over 4 square feet of turf. One teaspoon of pyrethrum (if available) may be mixed with the water instead of 1 tablespoon of detergent if you desire. Within 10 minutes, the above-ground insects should crawl to the surface of the grass as they try to escape the irritating substance. They then can be collected and counted. Use this technique in several places to get an average count of the insects present.

What we are seeing now is from earlier activity. It is too late to do anything now in terms of treatment. However I would watch early next summer and perhaps do an insecticide treatment if you had a problem this year.

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