FAQ's on White Grubs in Lawns
As we advance into summer, concerns are often raised about white
grubs in lawns and ways to manage them. Here is a summary of frequently
asked questions on white grubs in lawns.
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.
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, brown areas in 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
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 (refer to the next article
on dealing with moles).
Why Does My Lawn Have Grubs But Not My Neighbor?
Remember 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 This Year?
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
Can I Prevent Grub Damage?
There are some options to consider. One option is allowing the
lawn to go into dormancy as conditions dry in July (assuming there
is little rainfall), reducing the odds of grub damage. Another is
to closely monitor the lawn as we advance into late summer and be
ready to act if grubs start to appear. Insecticides such as diazinon
(still available in 2001) or trichlorfon (Dylox) can be applied
when grubs are first noticed to prevent large-scale damage. Insecticides
that take about 3 weeks to kill grubs, such as imidacloprid (Merit)
or halofenozide (GrubEx, GrubBGon) can be applied prior to noting
damage. Apply these in late July to lawns likely to show damage
(adults present, irrigating lawn). All of these insecticides should
be watered into the soil for best results. Lawns should also be
watered prior to application.
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.
June - July 2001: Summer
Mole Problems | Summer Lawn Care Tips
| Immigrant Plants | FAQ's On White
Grubs in Lawns