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!
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.
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.
Ironically:
- 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.