Solving real grub trouble

Learn their ways,
be certain they're the problem,
then hit them when it hurts the most.
Check to verify that the controls worked.
At every step, make the lawn stronger so it takes care of itself.

Know your enemy...

                                                                                     ...and use the knowledge to advantage

Grubs are baby beetles.
They eat plant roots.
They are like underground sheep -- grazers.
A plant can thrive even when its roots are being grazed, just as it can thrive even when its foliage is repeatedly mowed or shorn.
Some grub species eat only grass roots and are the prime culprits in lawn damage.
Grass-eating species won't lay eggs for new grubs and can't survive under non-grass plants.
So if you're solving a lawn grub problem there is no reason to apply grub killing products anywhere other than lawn.

If grass eating grubs occur in great numbers they can kill grass.

Turf management pros such as golf course greenskeepers monitor grub numbers.

Follow a greenskeeper's lead. Don't act unless grub levels rise to an intolerable number of grubs per square foot, usually more than 6.
Irrigated lawn can tolerate six to eight large white grubs per square foot.
Even non-irrigated lawn can withstand five such grubs per square foot.
Beetles lay eggs and hatchling grubs survive in large numbers only where conditions are just right.
In other places beetles may not lay eggs or eggs may suffer high mortality rates.
There is almost never a reason to treat an entire lawn for grubs.
Grub numbers are generally higher in some parts of a lawn than others, and some areas may be grub-less. (For example...)
Grubs move up and down in soil but do not move far laterally. A grub may slowly enlarge its grazing area during the time it is in a lawn but it does not migrate from its original spot to far parts of a lawn. When you see signs of grub damage in one area you can confine grub control to that spot.
Grubs occur in batches, commonly just one batch per year. Each grub species follows its own schedule to mature during one relatively brief period. The beetles emerge then to lay the eggs of the next generation.
The egg laying times of many lawn pest beetles' overlap in late summer.
Identify the problem beetle(s) and you can attack during the vulnerable young-grub stage. That kills the most grubs at a time when the lawn has not yet suffered much damage.
If you don't know which beetles you're battling, plan controls for the late summer.


Be certain that grubs are your problem

Count them!

Cutworm4769s.jpg GrubChafrDimen0848S.jpg

If you suspect grub trouble (here are the signs) use a spade to cut sod squares here and there in the lawn. Look for grubs under those flaps of grass.


Above: Which is a cutworm, which is a grub? Learn before you attack.

Total all the grubs you find and divide by the number of flaps you sampled. If the average count is more than six, consider grub killing tactics.

Don't be misled by those who profit in this war.
Grub control products are heavily promoted and the ad campaigns so effective that many people blame grubs for every lawn failure. Yet the more likely culprits are drought, soil compaction, disease, foot traffic, dog urine damage, etc. and the more effective fix is to improve the lawn.


Grub killer ads are misleading for being timed to push grub killing products in spring. That's when people are thinking about lawn care and so are likely to buy, yet it's the least effective time to go after grubs. If ads were timed to put grub killer in a gardener's hands when it is most effectively used, the ad campaigns would run in late summer.

Don't waste money or cause more collateral damage than necessary.
SandhillCr5061s.jpg  Grub control products are not cheap ($75 to $100 per yard
  per year is not unusual) and have side effects. Don't use
  any more than you must. Apply them only on the part of
  a lawn where grubs are present in damaging numbers.

 Above: A grub is pretty
safe in this form in spring!

  Left: There's a sandhill crane - grub link. Most people
  are surprised to learn how wide a ripple it is that has a
  grub at its center. That's why we say to consider
  collateral damage before poisoning or killing grubs.

Hit them where and when it hurts most

Young grubs are most easily killed because they are babies. That's when any creature is most susceptible to poisons and infection or attack by biological agents.
It is most effective to apply grub killers when the target grubs have just hatched. For most grub species that vulnerable time is in late summer and early fall. By spring they are old, tough and likely to survive attack.

Grub killers and biological agents must penetrate and spread in the soil to reach the most grubs. Use water to do this. Apply the killer right before a gentle, soaking rain or water slowly and thoroughly after the application.

Grub control products are based on:
- Poisonous chemicals that kill or fatally inhibit growth when eaten; or
- Biological agents such as fungi (milky spore) or predatory nematodes which actively attack grubs.
Some chemicals and agents simply do not work on old (springtime) grubs.

Grub control chemicals do not prevent future grubs.

Biological agents may persist and naturalize but they are not miraculous:
- Nematodes survive to hunt grubs only in consistently moist soil.
- Milky spore fungus thrives to infect beetle grubs only where temperature and moisture patterns suit them.

- Given water enough to enable nematodes, a lawn is probably too healthy to show grub damage, and
- milky spore is pretty much useless in the northern Great Lakes States.

Check to see if your controls worked

Insecticide may fail to penetrate. Beneficial nematodes may die in dry soil and milky spore perish before attacking any grubs.

Signs of damage should diminish or stop.

Re-sample to verify there are fewer grubs.

Don't keep doing the same thing if it doesn't work!

Help a lawn help itself next time

Grub damage is usually heavy in only some sections of a lawn, where the grass growing conditions are not good. There, grass plants are too weak to survive any additional stress. Improve the lawn and it can fend off grub damage on its own.


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 treat.

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 and 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.