Is it really grubs messing up my lawn?

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It is not trouble if you find a few grubs, even if you find two in every square of sod you lift. 

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 become regulars.

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 square foot.

The look of grub trouble:
In each season of the year
Any time
Based on grub count
How birds tell us


In summer:

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.

In fall:

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.

In 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 grass.

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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 form.


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.

GrubSpotClosen0817s.jpg GrubTroweln0814s.jpg


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.




Recognizing trouble
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 easy

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 cause damage

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 treatment.


Grub signs to be read any time:

  • 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 grub
                    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 resist
                    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 sandhill cranes.

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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