Dealing with White Grubs in Lawns
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White grubs are the most serious and destructive lawn insect
pests in Illinois. While not all lawns will get grubs and the extent
of grub damage varies from year to year, there are some important
points to consider concerning managing grubs in lawns. Grubs are
white in color, with a characteristic "C" shape body
when found in the soil feeding on lawn roots. Grubs are the larval
stage of beetles.
The most common grub species in our area is the annual white
grub, of which the adult is a tan chafer beetle. Eggs are laid
in the soil in mid-summer, primarily on well-watered lawns in full
sun, often near pavement. Damage from annual white grubs typically
starts in mid August and may continue until early October. Other
species may damage lawns in northern Illinois, but usually are
not as common as annual white grub. Monitoring and control of these
species is the same as for annual white grub. The true white grub
(May or June beetle), for example, typically has a 3-year life
cycle, meaning it could potentially damage lawns throughout the
season. Japanese beetle grubs can also occur in northern Illinois,
with timing very similar to annual white grub. Adult Japanese beetles
are serious defoliators of many ornamental plants.
Since grubs feed on the roots of lawn grasses, damage will appear
as browning of the lawn. Consider that this also could be due to
problems such as drought, poor soil, and diseases. However, grubs
are easy to find by lifting sod in damaged areas and checking the
root zone for the whitish grubs. Don't treat for grubs that don't
exist! Skunks and raccoons may tear up lawns in search of grubs,
even when grub numbers are relatively low. Typically a population
of about 8 to 12 grubs per square foot causes lawn damage that
requires control; whereas lower populations may not damage the
grass, they may attract skunks and raccoons.
Lawns showing damage from grubs may be treated with an insecticide.
Insecticides available for homeowners include trichlorfon, halofenozide,
or imidacloprid for control of white grubs. Heterorhabditis bacteriophora
nematode is an example of an alternative product for white grub
control that is available.
For all products, read and follow all label directions, then
apply to damaged areas. Water the insecticide into the soil immediately.
If treating a large area, stop after a portion has been treated
and water the material in, then complete the rest of the lawn area
needing treatment. Only treat in and around affected areas; grubs
may only be in a small part of the lawn. Imidacloprid and halofenozide
are suggested to be applied before grub damage appears. An example
of a way to use these products would be to apply in July to irrigated
lawns that are surrounded by dry lawns, especially when adult beetle
flight is high in areas with a history of grub damage.
Spring treatment for annual white grub is not suggested since
the grubs feed for a short period of time in spring and are reaching
maturity, thus are not controlled easily. In addition, turfgrasses
are actively growing at that time so usually don’t show damage.
August - September 2003: Cytospora
Canker of Spruce | Living with Snakes | Late
Summer Perennial Gardening Tips | Dealing
with White Grubs in Lawns | Pine Wilt