Get 'em before they sprout!
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Photo 1: Timing
Let grass growth determine the best
time for a preemergence herbicide.
Apply it after your second regular mowing
in the spring.
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Photo 2: Application
Apply crabgrass preemergence granules
with a spreader, especially around
driveways and walks and also alongside
the neighbor's crabgrass-infested yard.
The best weapon you have against
this annual weed is crabgrass preemergence
herbicide (also called crabgrass preventer).
You apply this product in the
spring before the crabgrass seed sprouts.
This granular herbicide works by creating
a chemical barrier at the surface of the
soil. As the seeds begin germination, they
take in the herbicide and die.
The most cost-effective way to apply a preemergent herbicide is to
use a fertilizer with crabgrass preventer added to it. These combination products
are readily available in the spring and cost about $20 for a 5,000-sq.-ft. bag at
garden centers. Apply it when you would normally apply your first application of
fertilizer, and do it just before it rains to work both the fertilizer and the herbicide
into the soil. The fertilizer will help thicken the turf. Thicker turf helps to squeeze
out crabgrass plants missed by the herbicide. Common brands include Ferti-
Lome’s Weed-Out, Sta-Green’s Crab-Ex Plus and Scotts Turf Builder.
This sounds easy enough, but where
you’re likely to get it wrong is in the when.
Apply too early and microorganisms and
natural processes in the soil break down
the herbicide. By the time it’s needed,
much of the product has lost its potency.
Apply too late and you’ve missed the early
stage of germination when the herbicide
works. There is nothing in preemergence
herbicide that
kills crabgrass
seedlings once
they’ve sprouted.
You’re just pushing
around that
spreader for the
exercise, not to
mention wasting
expensive
products. As far
as prevention
goes, you’re out
of luck until
next spring.
So how do
you select the
exact instant for application? Don’t
depend on the calendar. Pay attention to
your grass instead. Fill up the spreader with preemergence granules between the
second and third mowings of the year.
The window is short, only about a week
and a half, when the soil hits the ideal
temperature—about 52 degrees F. You
can also buy an inexpensive soil thermometer (sold at
garden centers) to monitor soil temperature. If you’re going to
err on timing your
crabgrass preemergence
application,
err on the
early side. While
you’ll lose some
effectiveness,
you’ll still probably
kill lots of crabgrass.
If you go
late, you’re likely
to miss early
sprouts.
If you’ve had a particularly bad crabgrass
problem, you’re not done for the
season. Chances are that the crabgrass will
germinate and spring up later in the summer.
Preemergence herbicides have a life
of about 50 days (check the label; product
life spans vary). Once that chemical barrier
breaks down, dormant crabgrass seeds,
which can remain viable for years, may
germinate into seedlings. Or if your yard
butts up against property that has a thriving
crabgrass crop, you can bet that thousands
of seeds will blow into your lawn,
just when your herbicide is calling it
quits. You don’t need to reapply the preemergence
herbicide to your whole yard,
but hit areas again where crabgrass
thrives, like right next to driveways and
walking paths. Because they absorb heat,
the soil around them gets warmer and
encourages the growth of crabgrass.
Wait to use grass seed after using an herbicide.
Reseed or Kill – Not Both
Herbicides that kill crabgrass will
also kill desirable grasses such as bluegrass,
ryegrass and fescue. If you treat your lawn with
a preemergent, you cannot seed. And if you
seed, you cannot use a preemergent herbicide.
The solution is to control crabgrass in the spring
and do your seeding in late summer or early fall,
making sure to keep these two chores at least
eight weeks apart. There
are a few preemergent
herbicides, such as
Tupersan, that are compatible
with newly
established seed, but
they’re expensive and
can be hard to find.
Check the Key Ingredient
There are many different trade names for “weed and
feed” products on the market. Chemical names can
be confusing. Look carefully at the ingredients panel for
dithiopyr, prodiamine or pendimethalin. These active ingredients,
which are sold under various brand names such as
Dimension, Barricade and Scotts Halts, will kill crabgrass in most
areas of the country and in many different kinds of turf. However, it’s always wise
to ask your local extension service which chemicals are best for your area and turf
species.
Yank 'em while they're young!
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Photo 1: Pull it
Pull out crabgrass as soon as you spot it. Young plants leave only a small hole in
your turf, which desirable grass types will quickly fill.
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Photo 2: What to look for
Young crabgrass plants perfect for
pulling have two to four sets of leaves
but no splayed seed heads.
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Photo 3: Immature seed heads
Immature crabgrass plants have
tight, green seed heads. They're
more difficult to remove, but it's still OK
to pull them.
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Photo 4: Mature seed heads
Fully mature crabgrass has splayed seed heads. It's best to leave it alone. Pulling
will leave a big hole in the lawn and spread up to 5,000 seeds per plant. The
plant will die in the fall. Then hit the area next spring with preemergence granules
to keep the seeds from sprouting.
OK, your lawn has been growing
for a couple of months and you notice
light green blades thickening up your
Kentucky Blue. Before you think your
lawn is having an exceptional season,
think again: It's likely to be young crabgrass
(see Photo 1).
Pulling, at this early stage, is a surprisingly
effective way to get rid of crabgrass.
But if the weed has pushed up three or
four rows of leaves, inspect it carefully
before you snatch it. If you spot a slender,
green seed head that is still closed and folded up against the leaves of the plant,
go ahead and pull it, too (Photo 3).
However, after the seed head tines have
spread out like a fork, leave it alone
(Photo 4). Otherwise you'll scatter scads
of seeds right over that nice big hole
you've just created by removing the
mature weed. You might as well be trying
to cultivate new crabgrass!
Come fall, seed bare and patchy areas. With good lawn care
practices, you'll soon
crowd out those fallen crabgrass seeds.
Spray stubborn patches!
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Spraying
Lightly mist masses of immature crabgrass with a postemergence herbicide. Usually
it's too embedded to pull without yanking lots of your desirable grass with it.
Spray postemergence herbicide
directly on crabgrass after it has sprouted. Pulling is equally effective,
but if the roots are deeply embedded
in your lawn, it may be tough to pull them
out without pulling grass chunks too. It's
not worth spraying a postemergence
product on crabgrass that has gone to seed. It takes about
two weeks for the herbicide to work,
which is about how long it takes the plant
to finish its seeding process. If it has gone
to seed, you're better off waiting for next
spring and applying a preemergence
product then.
Post-emergence herbicides are most
effective when the soil is moist and the
plants are dry. Read the label for specific instructions. Typically you apply it with a
hand pump sprayer. It's best to apply it on
a hot day when there's low wind. If temperatures
are too low, the product may be
ineffective. Unless the crabgrass is young,
you'll probably have to reapply the product
a few days later (according to the
label) to kill the plant.
After postemergence application(s),
keep an eye on the treated area. In
extremely dry conditions, water two days
after the application to aid absorption. If
your grass near the treated area is turning
brown, you probably were a little heavy
handed. Soak the damaged area with
water to dilute the chemical and avoid
further damage. Also be on the lookout
for new crabgrass sprouts. These will
require another herbicide treatment, or if
there aren't too many, simply pull them.
Be sure to seed these areas in the fall.
Don't waste your money on a
postemergence herbicide in the
fall, when the temperatures are
falling. The herbicide won't be
effective and the plant will
soon die anyway.
Fight Crabgrass With a Healthy Lawn
The best way to stop crabgrass is to
shade it out with a thick, healthy
lawn. A thick lawn provides a dark
canopy of grass blades over the seeds,
so they won't sprout. Follow these good
grass-care practices.
Watering: A thorough watering once
a week will encourage the grass's root
system to go deeper, making the whole
lawn more hardy and heat tolerant.
Avoid short, frequent waterings. These
“sips” will promote a shallow, weaker
root system in your lawn.
Mow: As a rule, grass should be
mowed to a height of 2 to 3 in. Mowing it shorter than 2 in. will reduce the
grass's vitality and give weeds a
chance to move in. Be sure to keep
your lawn mower blades sharp so
they won't tear the grass. Leave grass
clippings on the lawn as a natural
fertilizer.
Reduce compaction: Weeds thrive
in areas where compacted soil
deprives the grass roots of the air and
water circulation they need. If your
yard is prone to compaction, rent and
run an aerator over it every other
year, especially if your soil contains a
lot of clay.
Fertilize right: Avoid lawn fertilizers
that say “quick green-up” on the
label. These have excessive nitrogen
ingredients that will actually weaken
your lawn over time, making it more
susceptible to weeds. Instead, select
a fertilizer product with half of its
nitrogen in a slow-release form. For a
1,000-sq.-ft. lawn, use less than 3 lbs.
of nitrogen annually.
Reseed: Weed-damaged or thin
areas should be seeded (sometimes
called “overseeded”) in the fall, when
the days are warm, the nights are cool
and you have dew in the mornings.
Apply a double dose near hot spots
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Some spots need special attention
Lawn near driveways, sidewalks
and curbs or on south-facing banks absorbs
a lot of heat during the summer months,
which makes it more susceptible to crabgrass.
Limit crabgrass growth in these areas
by doing a targeted double treatment. After
you’ve treated your entire lawn, go back and
make another pass, about 6 to 8 ft. wide,
along these areas (and make sure to sweep
it off hard surfaces afterward). This will help
keep crabgrass from taking hold along these
heat absorbers.
Kill it all and start over!
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Photo 1: Expose bare soil
Kill off patches of lawn with nonselective
herbicide in the fall if more
than half the area is weeds. When it's
safe to replant (check the herbicide
label), soak the patch with water and
rake off dead grass and thatch to bare
the soil.
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Photo 2: Furrow the dirt
Create 1/4-in.-deep furrows every
2 in. using a flat shovel. This will
give your seeds a better chance to settle
into the moist soil.
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Photo 3: Seed
Toss grass seeds into the patch and
keep the soil moist to the touch until
the grass becomes established. Mow the
new grass when it's 3-1/2 to 4 in. high.
While we all admire those who
relentlessly defend their turf against crabgrass,
there comes a time when the best
strategy is to give up. That time is when
your lawn only has 30 to 40 percent desirable
grass left in a given area and the rest is
lost to crabgrass and other weeds.
Begin by killing all the vegetation. On a
low-wind day, apply a nonselective herbicide
that is approved for lawn use, like
Round-Up or Kleen-Up. Follow the label
directions exactly. Depending on the
product, weeds and grass will die and dry
up in five to 14 days following application.
Then renovation can proceed.
Thoroughly soak the area to give your
new grass its best chance for a good start.
Check your watering depth by pushing a
spade into the ground and pulling it back
to get a deep view of the soil. If the soil is
moist to a depth of 6 to 8 in., you're ready.
For patchy bare areas and turf-free areas
up to about 8 ft. square, use the spade
technique for seeding (Photo 2). It's very
effective, although it would be slow and
tedious on areas that are much larger.
Scuff up the dead vegetation with a rake
and, using a spade, make 1/4-in.-deep furrows
about 2 in. apart. Broadcast your
grass seed, then flip a rake upside down
and knock the seeds into the furrows.
These furrows ensure that the seeds will
make good contact with soil; they provide
some moisture-retaining shelter as well.
Then be sure to keep the seeds and soil
moist. Continue to baby your new grass
until after its first mowing. Do not apply
crabgrass preventer to freshly planted
areas.
Natural crabgrass control
Consider Chemical-Free Control Methods
Preemergent herbicides are the most effective and economical
way to control crabgrass. But if you’d rather not use
herbicides, you can try hand-weeding individual crabgrass
plants in late spring before they get too big. They
pull easily in soft ground after a rain.
Corn gluten meal (CGM), a corn byproduct, is another
method used to control both crabgrass and broadleaf
weeds such as dandelions and clover. It releases a protein
that slows the development of weed seedling roots.
CGM requires a heavy application rate (20 lbs. per 1,000
sq. ft.), which makes it cumbersome to use and expensive. It costs about $30
for 25 lbs. at garden centers.
