White Grub Problems In Turf
White grubs are the most serious and destructive turf insect
pest in Illinois. While not all turf areas will get grubs and
the extent of grub
damage varies from year to year, there are some important points
to consider concerning managing grubs. Grubs are white in color,
with a characteristic "C" shape body when found in the
soil feeding on grass roots. Grubs are the larval stage of beetles.
Annual White Grub Larva
The most common grub species in our area is the annual white
grub. The adult beetle, called a masked chafer, lays in the soil
in mid-summer, primarily on well-watered turf 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 turf 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 turf throughout the season. Japanese beetle grubs 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 turfgrasses, damage will appear
as browning of the lawn or other turf area. 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 turf
in search of grubs, even when grub numbers are relatively low.
Typically a population of about 8 to 12 grubs per square foot
causes turf damage that requires control; whereas lower populations
may not damage the grass, they may attract skunks and raccoons.
Annual White Grub Damage
Turf areas showing damage from grubs may be treated with an insecticide.
Insecticides for white grub control include trichlorfon
(Dylox); bendiocarb (Intercept), halofenozide
(Mach 2, GrubBGon, GrubEx), or imidacloprid (Merit,
formerly GrubEx) 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 dont show damage.
Other insects may attack lawns in northern Illinois but severity
of damage changes from season to season and also by location.
Examples include sod webworm, billbug, chinch bug, and aphids.
These insects differ from grubs in that they are feeding at or
above the surface of the soil and usually are not as destructive.
Written by Bruce Spangenberg, former Extension
Educator, Horticulture. University of Illinois Extension.