What grub trouble looks like
To identify grub trouble, look for the signs that a lawn is
actually stressed, or pay heed if grub eating birds or skunks
If you see those signs, sample the lawn by turning over ten
squares of sod and counting the grubs you find. Don't be concerned
until you count over 60 grubs -- an average of more than 6 per
The look of grub trouble:
In each season of the year
Based on grub count
How birds tell us
Where there are a great many grubs the lawn's above ground parts
wilt in the heat even when the lawn's just been watered. Wilted
patches look dull and dark in the hot afternoon. These patches may
look fine by the next morning when it's cool. Check there for root
damage and tiny new grubs.
Heavily damaged areas of grass may die. The rootless remains can
be peeled away like a cheap toupee. If the grass dies in fall, even
the remains may be gone by spring.
You may see summer's and fall's symptoms or there may be spots that are totally bare, where grubs fed
heavily enough to kill the grass. By now, the grass' remains have
blown away and the bare spaces may be grubless but you'll find a
concentration of grubs around its edges, beneath still living
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Right, below: One spring we helped diagnose and solve this
lawn problem. Grubs were no longer under this bare patch, since
predators had eaten many. The survivors were under the still-live
grass along the edge.
Grub damage is most apparent each year in spring as grubs near the
end of their development and are about to mature. However, they
are hardest to kill at this stage. They are almost immune to
chemical controls once they begin the transformation to their adult
If you see grub trouble in spring, focus on replacing or
improving damaged lawn.
Right, and below: In this case we focused on lawn
health, not grubs. We did mark the calendar to check in late summer
and move against grubs if the next generation also caused trouble.
The healthier lawn was not so easily damaged but if it had been,
late summer would have been when to act to control grubs -- that
would have been the next time grubs were present and young enough
to be vulnerable.
Right: This European chafer grub may be 30 to 50 times larger than it was last
September. It can also do that much more damage and is that much
tougher to kill than late summer and fall grubs.
by grub body count
It's potential trouble if there are more than six grubs on
average below squares of sod lifted or peeled back.
Thresholds* for large white grubs:
European chafers, Japanese beetles, and Oriental beetles
0-5 grubs/ square foot: Rest
Fewer than five grubs per square foot is a low population. You
don't need to act.
6-9 grubs/ square foot: Think about
improving your lawn's health
Is your grass dense, with a healthy, robust root system, and can
you irrigate? If so, just keep it watered. It can probably
withstand grub populations of 6-8 per square foot, or more.
10 or more grubs/ square foot: They may
Ten or more grubs per square foot will likely cause damage,
especially if the lawn is otherwise stressed. In most
circumstances, you'd be justified treating where populations are
this high. Several weeks after treating, sample in a few locations
to determine whether treatments were effective.
*From research in upstate New York indicating that
only 20 percent of home lawns and golf course fairways require grub
Grub signs to be read any
- Patches of lawn may have trouble but not the whole lawn.
Sections that tend to be dry because of irrigation or soil problems
may become grub hot spots.
The lawn we've shown you in this article was typical in having
damage only on a south facing slope. There sun, gravity and
compaction all combined to make the grass dry and stressed.
We raked away the dead grass, aerated, reseeded and the
homeowner concentrated on watering more there.
We did not treat to kill the grubs, which were old enough to
and not numerous enough to bug healthy lawn.
- Insect eaters such as skunks may dig many small, shallow holes
throughout the area. (Raccoons
will hunt 'em, too.)
- Grub eating birds such as
starlings may frequent the lawn in bunches.
Grubs die by the hundreds when a mob of starlings works a
lawn. But other birds dine on them, too, including this squad of
We appreciate the birds for their de-grubbing work and also the
aeration they provide. We paid over $100 last time we
rented a good core aerator machine for the day. These four sandhill
cranes, walking a tight pattern back and forth across this lawn,
did at least as much for this lawn as an aerator could.
The birds probably applied some fertilizer, too.
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