How do I know if I have grubs in my lawn?
White grubs feed on the roots of grasses, so lawns will show wilting
and browning of irregular shaped areas. Certainly there could be
many reasons for lawns browning, especially in late summer when
most grub damage occurs. Always check the root zone of affected
areas for the white, c-shaped grubs. Carefully pull back the sod
in suspect areas, in particular the marginal areas where brown grass
meets green grass, and look for the grubs. Usually a population
of about 10 or more grubs per square foot will lead to browning
of the lawn.
||Peeling back a damaged lawn
area has revealed these white grubs in the soil as the cause.
Keep in mind other factors that can lead to poor rooting and are
mistaken for grubs. For example, lawns in shade areas often have
weak roots and are pulled-up easily. Grubs do not typically appear
in shade lawns. Also, many lawns were easily pulled up this spring
and grubs were blamed. Once grass dies, regardless of the cause,
roots will rot away and the grass is very easy to tear out. So trying
to diagnose grub damage from the previous season as the cause of
a dead lawn area in spring is very difficult to do, even if limited
roots are found in an area of dead grass.
|Raccoons and skunks have
damaged this lawn area looking for grubs.
Another sign of grubs is damage from skunks and raccoons digging
up lawns in search of grubs to eat. This usually happens at night.
Moles may or may not be feeding on grubs so are not a reliable indicator
of grub problems.
Why does my lawn have grubs but not my heighbor?
Keep in mind the adult stage of the grub life cycle is a beetle,
which can fly. Random chance is part of the answer. But adult beetles
usually lay eggs in full-sun lawn areas with adequate soil moisture.
The masked chafer (annual white grub) and Japanese beetle lay eggs
in July. So if the weather has been dry but your lawn is watered
and surrounded by dry lawns, it is a prime target for egg laying.
How can I predict if my lawn will have grub damage
It is difficult, as insects can go in cycles and many factors influence
the chances of grubs appearing in your lawn. Lots of adult beetles
on the lawn in July is one indication. Masked chafers, the adult
of the annual white grub, are tan beetles active shortly after sundown.
Japanese beetles fly during the day and feed heavily on many ornamentals.
Noting these adults and then having irrigated lawns surrounded by
drier turf increases the chances of grub damage to your lawn. Watch
lawns closely starting about mid-August and continuing into September
for wilting and browning areas, and then check the root zone for
|The masked chafer is the
adult beetle which lays eggs becoming the annual white grub
||Japanese beetles, which have
been increasing in Illinois, feed on many plants as adults and
lay eggs in lawn areas which may become a grub problem later
in the season.
Can I prevent grub damage?
There are some options to consider. One option is allowing the
lawn to go into dormancy if conditions dry due to lack of rainfall
in July, reducing the odds of grub damage since the adult beetles
look for green lawns with good soil moisture for egg laying. The
downside is the lawn will be brown and dormant. Also, this may not
be reliable if rainfall keeps grasses green throughout July, although
if all lawns are green, the chances of significant grub damage on
any one lawn are low since the adult beetles tend to disperse and
lay eggs over a much broader area under this scenario.
Another option is to closely monitor the lawn as we advance into
late summer and be ready to act if grubs start to appear. Watch
for grass areas going off-color and just starting to brown, in particular
those areas that have been irrigated. Check the root zone for small
white grubs. Insecticides such as diazinon or trichlorfon (Dylox)
can be applied when grubs are first noticed to prevent large-scale
Other insecticides such as imidacloprid (Merit) or halofenozide
(GrubEx) can be applied prior to noting damage, such as in late
July to lawns likely to show damage (adult beetles present, irrigating
lawn). All of these insecticides should be watered into the soil
for best results. Lawns should also be watered prior to application.
With all insecticides, read and follow label directions. To confirm
what a product contains as active ingredient, check the active ingredient
section on the front of the label.
What about using organic controls for grub control?
Heterorhabditis bacteriophora nematodes have shown good
results for white grub control. Nematodes are very small unsegmented
worms. This particular species will search out white grubs and after
entering the grub, release bacteria that kills the grub. This product
is available in mail order catalogs, often sold as Hb nematodes.
This product should be applied late in the day to lawns with adequate
soil moisture and then watered in immediately.
What should be done after grub damage has occurred?
If significant grub damage has occurred, the lawn will need some
renovation work in early fall. Rake away dead debris. Water the
lawn area, as some of the grass with damaged roots may recover,
especially if the weather cools down. Bare or thin areas may need
some reseeding. Labor Day is a good target date for lawn renovation
work in northern Illinois.