Weeds
That Grow in Lawns
There
are two kinds of weeds that grow in lawns; weeds that look like
grasses, and weeds that look like salad. Here's how to recognize and
deal with weeds in your lawn.
Weeds
That Look Like
Grasses:
Poa
Annua (Annual Bluegrass)
Poa
Annua is an annual grass that starts in fall from seed, grows
through the winter, then dies in the summer. It mimics lawn grasses
because it looks similar to desirable grasses. It causes brown areas
when it dies off in early summer (as soon as it gets warm). It makes
seeds just before it dies; the seeds wait all summer and start new
plants again in late fall. It can be identified in winter by examining
the blades; some blades will have wrinkles running across the blade.
The wrinkles are caused by a nematode parasite that only affects poa
annua.
Control: Use a pre-emergent seed killer around Halloween and again in
early January for several years in a row. The seeds will sprout but
will be killed by the pre-emergent. Pre-emergent is like birth control
because timing is everything. Using a pre-emergent in summer to control
poa annua is a waste because no poa annua seeds are sprouting; they
wait untill fall and so should you. A good pre-emergent is "Halts" by
Scotts. It is available alone or in a fertilizer mix and is listed to
control poa annua. There are other pre-emergents available; look online
for options.
Crabgrass
Crabgrass
is an annual grass that
starts in
spring from seed, grows through the summer, then dies in the fall.
Seeds are produced within two weeks from sprouting and continue all
summer long. Plants are easy to pick if there are just a few. To pick
crabgrass, run your finger around the base of each plant to isolate it
from the desired lawn grasses, then grab the center (plus a pinch of
dirt) and pull
back and forth and right and left while pulling up. The roots are very
shallow and pull up easily.
Control:
Keep the lawn mown tall to prevent seeds from starting. Do not
water
daily because seeds need daily watering to become established. Pick or
spray existing plants with Ortho Crabgrass Killer or Bayer Advanced
All-in-One Lawn Weed Killer. These chemicals will not damage the lawn
grasses when used properly. Use a pre-emergent seed killer around
mid-March and again in
early July. The seeds will sprout but will be killed by the
pre-emergent. Pre-emergent is like birth control because timing is
everything. Using a pre-emergent in winter is a waste because crabgrass
seeds are not sprouting; they wait untill spring and so should you. A
good pre-emergent is "Halts" by Scotts. It is available alone or in a
fertilizer mix and is listed to control crabgrass.
Nut sedge / Nut grass
Top: Uprooted Bottom: Growing in
a lawn
This is really a
sedge, not a grass. When cut, the stem has three sides. Pulling it up
will
do no good at all because there are small nut-like roots that break off
and stay in the soil. The nuts can lie dormant for years and then
sprout. It is usually brought in by re- sodding and is unnoticed when
closely mowed.
Control:
Although seeds will spread this plant, they rarely form in
lawns because they get mowed off. The only way to control nut
sedge is
with a spray such as Ortho Crabgrass Killer or Bayer Advanced
All-in-One Lawn Weed Killer. Both products seem to work, but repeated
applications are necessary to kill new sprouts produced by the
previously dormant nuts in the soil.
Sedges
are ancient
plants and are difficult to kill. Be aware that
proper mowing and watering are required to prevent the lawn grasses
from becoming stressed out during treatment.
Bent Grass
Some
people get bentgrass in their lawns and it looks like the image to the
left. If the lawn is 100% bentgrass, there's no problem, but when it
invades a fescue or bluegrass lawn, it contrasts badly due to its fine
texture and a different shade of green. Bentgrass is the grass used on
putting greens, and is much more difficult to grow because it creates
thatch and is susceptible to insects and fungus.
Bentgrass
seeds are
tiny and usually arrive with the
wind or in bird droppings. Seeds will form but not unless it is
allowed to grow very tall (over 1 foot). It is a perennial grass.
Control:
Very
difficult to eradicate, digging it out won't work, no
selective weed killer is known. However, some suppression and control
can be had using Turflon weed killer. Turflon has a damaging effect on
bentgrass but requires repeated applications.
Foxtails
Foxtails
are a summer annual grass that can be very annoying. It starts in
spring, grows all summer, then dies in the fall. There are several
species of foxtails that grow in lawns, but they are all annuals.
Control:
Foxtails
can be controlled two ways: spraying existing plants
or preventing seeds using pre-emergent. Use Ortho Crabgrass Killer to
kill existing plants, or use Scotts Halts pre-emergent in the spring to
kill the seeds before they emerge.
Keep the lawn mown tall to prevent seeds from starting. Do not water
daily because seeds need daily watering to become established.
Goose grass
Goose
grass
is a summer annual grass that can also be very annoying. It
starts
in spring, grows all summer, then dies in the fall.
Control: Goose
grass can be controlled two ways: spraying existing
plants or preventing seeds using pre-emergent. Use Ortho Crabgrass
Killer to kill existing plants or use Scotts Halts pre-emergent in the
spring to kill the seeds before they emerge.
Keep
the lawn mown
tall to prevent seeds from starting. Do not water
daily because seeds need daily watering to become established.
Quack grass
Quack
grass
is a perennial and is difficult to control since they resemble turf
grasses in their tolerance to herbicides. They tolerate close mowing,
and can persist indefinitely. Even though they stay green all year
long, they have different color and growth rates, so they are
objectionable as turf grasses. This grass spreads by underground
creeping stems.
Control:
there is
no effective chemical control of quack grass short of
killing the infected area, sterilizing the soil, and starting over.
Bermuda grass
Bermuda
grass is not technically considered a weed, but many of us don't like
it and try to get rid of it. Some call it Devil's grass and other
derogatory names. Bermuda is a subtropical grass that always goes
"dormant" in the winter. Since it came from tropical climates, it does
not tolerate the colder winters in the Bay Area. Seen here is an area
of dormant Bermuda.
If
your lawn is mostly Bermuda
and has little to no green grass in winter, you can scalp and overseed
in late fall to establish fescue that stays green all year long,
provided you don't encourage the Bermuda to resume activity by cutting
your lawn too short in spring and summer.
If
your lawn has
Bermuda creeping in, you can control it and beat it
back to submission, provided there are no large areas of strictly
Bermuda. If it's mixed into your fescue or bluegrass lawn, try using
Turflon D broadleaf weed killer. You'll likely need to get it online
or possibly at your local Ewing Irrigation store. Don't use Turflon D
if your lawn is bentgrass, unless you want to kill the bentgrass. This
stuff only works when the target grass is active, so don't use it on
dormant Bermuda!
Weeds
That Look Like
Salad:
Dandelion
Would
you eat this weed? Many people do (dandelion greens) but they really
don't belong in a lawn! Dandelions are biennial plants that persist in
turf for years. They are by far the easiest to control because they are
susceptible to all broadleaf weed killers. A newer variation has a
flower with a very short stem in order to avoid being mowed off.
Control:
Dandelions
are easily killed using Ortho Weed-B-Gon or Bayer
Advanced All-in-One Lawn Weed Killer. These chemicals will not damage
the lawn grasses when used properly.
Pulling
dandelions
out is a risky choice because the tap root may break
off, growing as large as a carrot before sending up new growth. As with
all broad leaf weeds, spray in between mowing and do not water for
several days.
White Clover
Clovers
are broad-leaved weeds
that are of the legume family. They produce their own nitrogen and are
usually very green. Clover is a perennial plant that will grow anywhere
but loves lawns due to the regular watering. Clover spreads in the
lawn, producing burrs that contain seeds that can spread rapidly.
Control:
Clovers
are easily killed using Ortho Weed-B-Gon or Bayer
Advanced All-in-One Lawn Weed Killer. These chemicals will not damage
the lawn grasses when used properly.
Pulling
clover out
will not succeed because of the stems growing
underground. As with all broad-leaved weeds, spray in between mowing
and
do not water for several days.
Mallow (pennywort)
Mallow
is a perennial plant
that resembles ground ivy. It spreads from a central root and can be
successfully pulled out if there are not too many plants. Usually,
there
are stands that resemble dichondra. The leaf edges look serrated.
Control:
Mallow ivy is killed using Ortho Weed-B-Gon or Bayer Advanced
All-in-One Lawn Weed Killer. These chemicals will not damage the lawn
grasses when used properly.
As
with all broad-leaved weeds, spray in between mowing and do not water
for several days. You may need several applications for full control.
Spurge
Spurge
is a perennial plant
that leaks a milky fluid when broken. There are several types of spurge
including spotted spurge, which has a redder stem and a purple spot on
each leaf. Spurge creates seeds below the mower's blades so getting
control is important.
Control:
Spurge is
easily killed using Ortho Weed-B-Gon or Bayer
Advanced All-in-One Lawn Weed Killer. These chemicals will not damage
the lawn grasses when used properly.
As
with all broad-leaved weeds, spray in between mowing and do not water
for several days.
Oxalis
Don't
confuse this weed with
clover - it's MUCH smaller and has tiny yellow flowers. A relative of
woodsorrel, oxalis is a woody herbaceous plant - unlike clover, which
is a legume. Oxalis has a nasty habit: it has exploding seed heads! As
each tiny yellow flower dies and dries up, a seed bud forms, and a
powerful spring mechanism
grows inside the bud. When
the trap is sprung (usually by a passing lawn mower or a gust of wind),
multiple seeds are thrown out up to 18" away from the plant. The seeds
germinate, and make new oxalis plants.
Control:
Oxalis is
easily killed using Ortho Weed-B-Gon or Bayer
Advanced All-in-One Lawn Weed Killer, but you will need to spray
several times to get the newly sprouted plants, as the seeds are
unaffected by the weed killer. These chemicals will not damage the lawn
grasses when used properly. As with all broad-leaved weeds, spray in
between mowing and do not water for several days.
Black Medic
This
weed looks like clover but
it isn't related. It was used as a medicinal treatment in ancient times
and was the base for tonics and potions. Its leaves are smaller than
clover and bigger than oxalis. It sometimes has a purple or darker
color
and usually grows in the shade.
Control:
Black
medic is easily killed using Ortho Weed-B-Gon or Bayer
Advanced All-in-One Lawn Weed Killer, but you will need to spray
several times to get the newly sprouted plants, as the seeds are
unaffected by the weed killer. These chemicals will not damage the lawn
grasses when used properly.
As
with all broad-leaved weeds, spray in between mowing and do not water
for several days.
Ground Ivy
Ground
ivy looks like giant
mallow except that it has lobed leaves instead of serrated leaves. It
has stubborn runners that are not easy to pull out. There are
several types, but all are controllable when growing in turf.
Control:
Ground ivy is killed using Ortho Weed-B-Gon or Bayer Advanced
All-in-One Lawn Weed Killer, but you will need to spray several times
to get complete control.
These chemicals will not damage the lawn grasses when used properly. As
with all broad-leaved weeds, spray in between mowing and do not water
for
several days.
Mouse Ear Chickweed
This
weed has several
variations, "mouse ear" and "common." They are similar to all
broad-leaved
weeds in that they are controlled using broad-leaf weed killer.
Control: Chickweed is easily killed using Ortho Weed-B-Gon or
Bayer Advanced All-in-One Lawn Weed Killer, but you will need to spray
several times to get the newly sprouted plants, as the seeds are
unaffected by the weed killer. These chemicals will not damage the lawn
grasses when used properly.
As
with all broad-leaved weeds, spray in between mowing and do not water
for several days.
Wild Violets
These
plants are the worst to
try to pull because even the smallest root will propagate and make new
plants. The good news is that they respond to the same weed killers as
other broad leaved weeds.
Control: Violets are easily killed using Ortho Weed-B-Gon or Bayer
Advanced All-in-One Lawn Weed Killer, but you will need to spray
several times to get the newly sprouted plants, as the underground
stems
are unaffected by the weed killer. These chemicals will not damage the
lawn grasses when used properly.
As
with all broad-leaved weeds, spray in between mowing and do not water
for several days.
Red Sorrel
Red
sorrel is a persistent
perennial weed that should be eradicated promptly because it spreads
throughout the lawn area quickly. The controls that are most effective
are made to young plants and plants that are growing new leaves.
Control:
Sorrel is
controlled using Ortho Weed-B-Gon or Bayer Advanced
All-in-One Lawn Weed Killer, but you will need to spray several times
to get the newly sprouted plants, as the seeds are unaffected by the
weed killer. These chemicals will not damage the lawn grasses when used
properly.
As
with all broad-leaved weeds, spray in between mowing and do not water
for several days.
Please
use caution
when spraying your weeds. Weed killer is a poison, but if handled
properly can be completely safe. If you have pets, do not allow them to
come into contact with treated areas until the lawn is completely dry.
If you have cats, be sure that the cats do not eat grass that has been
sprayed.
Does aerating help
control or spread weeds? Click HERE
to find out!
If
you have questions this page does not answer, call Green Lawns
at 800 281-6482.
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