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