University of Illinois Extension
Bruce Spangeberg

These articles are written to apply to the northeastern corner of Illinois. Problems and timing may not apply outside of this area.

Stateline Yard & Garden

Grubworms and Sod Webworms
Not the Same Pest

May 29, 1997

White grubs and sod webworm are two separate insect pests of lawns. Confusion sometimes exists between the two, especially when white grubs are referred to as grubworms. While neither one is currently a problem on area lawns, there have been several questions about these pests in recent weeks.

White grubs are the most serious lawn insect pest here in northern Illinois. Although sometimes called grubworms, they are not worms. Grubs are the larva stage of beetles. Annual white grub, the larva of the masked chafer beetle, is the most common species in our area.

Grubs feed on the roots of grass plants, causing lawns to wilt and turn brown as a result of this feeding. Damage typically shows in the second half of August and into September. We cannot predict now whether white grubs will be a serious problem or not in 1997. In 1996, we saw very little grub damage. Thus we do not suggest treating lawns now for grubs.

Larva of sod webworms are actually caterpillars that feed on the leaf blades of grasses. The adult is a small, buff-colored moth that flies out of the lawn when disturbed and lands a short distance away. The caterpillars feed at night, and heavy feeding causes brown areas of stubble in lawns.

We usually start seeing the first generation of sod webworms about mid-June. Often, there is a second generation damaging lawns in early August. Once again, it's not possible to predict damage now.

Since lawn insect pests vary from year to year, it is hard to predict damage. Applying insecticides well in advance of seeing any damage is not a sound pest management practice. It is not unusual to see no insect damage on a lawn during the course of a season. Thus following a complete step-by-step lawn fertilization program that automatically includes an insecticide application in mid-summer is not a sound way to care for your lawn.

The best advice regarding lawn insects is to wait and see if in fact a significant population and damage potential exists, then take steps to control them. Stay tuned to this website during the season for updates on lawn pest problems. Also access the Lawn Talk fact sheets.


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