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Chapter 11: Weed
Control
Bud Brownmud
was finally proud of his lawn. It had taken an entire weekend
to put it in, but then the seeds had sprouted, and now, a
month later, his lawn was lush and green. But wait — what
was that over there near the street? It looked like a weed.
There weren't supposed to be weeds growing in his nice, new
lawn, were there? He knew just who to ask.
"Hey Scott,"
he yelled over to his neighbour who was busy trimming a hedge.
"What's that?" Bud asked, pointing at the suspicious
plant.
Scott looked up with appraising eyes. "Monkey
grass. It's a weed. Just pull it out, and make sure you get
the root."
Bud pulled the weed up, noting with
satisfaction he'd captured the root ball. Then he took a
closer look around. Uh-oh - over in the far corner, near the
house, were a whole lot more weeds and he didn't feel like
pulling them all. "Scott, is pulling all you can do for
weeds?"
"No, it's not. Let's talk
about them," Scott replied.
What are weeds? It
depends ...
It's been said that one man's
weed is another man's flower. There is no set definition of a
weed, other than an unwanted form of plant life. For instance,
stray dandelions are frequently considered nuisance weeds in
lush lawns, yet out in natural settings, they fit right in as
wildflowers. There are even organic farmers who grow
dandelions for their nutritious greens, and to make wine from
them.
When it comes to controlling
what you deem to be weeds, there are two basic routes you can
take. By far and away the hardest route is also the safest one
for your health and the long-term health of the planet: going
organic.
An organic approach to weed
control involves lots of hand-pulling, strategic release of
ladybugs and other beneficial insects, and judicious use of
natural sprays such as soapy water.
Turn High Grass Into Cold
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The other approach is to use
chemicals on your lawn to control weeds. This is easy and
takes much less time, but if you have small children, pets, or
a nearby garden, you may wish to think long and hard about
dumping toxic chemicals all around your home just to get rid
of a few unwanted plants.
Weed Identification and
Characteristics
 Lawn weeds may conveniently be divided into
two classes based on the way in which they emerge from the
seed. Monocots emerge with a single seed leaf whereas dicots
emerge with two seed leaves. Most monocot weeds found in
turfgrass are from the family Gramineae and are termed weedy
grasses. Examples include crabgrass, annual bluegrass, tall
fescue, and quackgrass. Dicots, on the other hand, are termed
broadleaf weeds and include such plants as dandelion, clover,
ground ivy, knotweed, and plantain.
Weedy grasses and broadleaf
weeds are further divided into groups according to the plants'
length of life. Perennial weeds have a life of more than two
years, though new seeds may be produced every year. Biennial
weeds have a life of two years, generally storing up food
reserves in the leaves and roots the first year and producing
seed in the second year. The biennial weeds often are grouped
with perennial weeds since control is similar. Annual weeds
germinate from seed, grow, flower, and produce seed in less
than one year. Summer annuals germinate in the spring and
mature in the fall, whereas winter annuals germinate in fall
or late winter and mature in late spring.
Effective control of weeds in
turf is based on correct identification. Many books and charts
are available to help in identifying common lawn weeds. For
additional help in weed identification, inquire at your county
extension service.
Methods of
Control-Cultural
The most effective method of
controlling lawn weeds is to maintain a dense and vigorously
growing turf
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Helpful Hints
If you think you’ve done everything
possible to prevent weeds yet they’re still cropping up,
your pets may be to blame. It’s been proven that weed
seeds eaten by animals and passed through their bodies
remain active, so your pets may be finding weed seed in
grass in other yards and bringing it back to yours
without even realizing it. Make sure you do a daily
check for pet waste to help cut down on the chance that
weed seed is in your
yard.
| cover. Weeds are
often an indication of problems in the grass plant
environment, and killing the weeds without correcting the
underlying problem will lead to unsatisfactory results. For
example, a problem with knotweed is usually an indication of
severe soil compaction. Control of knotweed without correction
of the soil compaction will only lead to sparse soil cover
until the area is again invaded by weeds that grow in
compacted soil.
Often turf weeds can be controlled
simply by altering the cultural practices to favor the grass
plants rather than the weeds. The cultural controls may
include raising (or lowering) the mowing height, changing the
frequency of mowing, lengthening (or shortening) the period
between irrigations, increasing (or decreasing) the
application of fertilizer, or aerifying the
soil.
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A combination of proper
cultural practices plus prudent use of chemical is sometimes
necessary to effectively control weeds in turf. Whenever
herbicides are used, container labels should ALWAYS be read
and followed carefully.
Pre-emergence
Herbicides
Pre-emergence
herbicides affect germinating seeds. To be effective, the
herbicide should be applied two to three weeks before weed
seeds germinate. Consequently, pre-emergence herbicides are
most effective against annual weeds. For control of summer
annuals such as crabgrass, application of pre-emergence
herbicides between May 5 and May 20 in temperate climates is
most effective in a normal year.
Post-emergence
Herbicides
Post-emergence herbicides are
used to kill weeds after the weed plants are up and growing.
To be effective, most post-emergence herbicides must be
absorbed through the leaves; consequently, liquid sprays
generally work better than dry, granular materials. However,
granular formulations may be the most practical way for
homeowners to apply these materials.
Post-emergence herbicides are
most effectively applied when weeds are young and growing
vigorously.
Selective post-emergence
herbicides are usually used to control annual, biennial, and
perennial broad-leaved weeds because they will kill many
broadleaf plants without damaging grass plants. These
herbicides can severely damage or kill trees, shrubs, and
flowers; thus, they should be used with great care near these
plants.
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Revealed
Post-emergence herbicides may
be applied any time the weeds are actively growing, the air
temperature is 15-27(C (59-81(F,) there are no winds, and
there is no rain in the forecast for 48 hours. Most effective
control of perennial broadleaf weeds is obtained when
post-emergence herbicides are applied in early fall (August
15-October 15) or in the spring (May 1-June 1). For some
weeds, repeated application at 20-30 day intervals may be
required for control.
Nonselective post-emergence
herbicides kill all plants, both desirable and undesirable.
These
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Helpful Hints
Have a floral or vegetable garden area near or within
the borders of your lawn? If you’re weeding other plants
near the grass, don’t lay the pulled weeds on the grass…
you’re just begging for spreading. Instead, place them
directly into a trash area or on a cement surface, then
dispose of them
properly. | herbicides
can be used to spot treat perennial grassy weeds that are not
affected by selective herbicides. To spot treat an area,
thoroughly wet the weed foliage with herbicide solution.
Pre-emergence or selective
pre-emergence granular materials may be applied with a
fertilizer spreader. The spreader must be calibrated to apply
recommended rates. The preferred method of application is to
apply one-half the recommended rate in one direction and
one-half at a right angle to that direction.
Compressed air sprayers or
sprayers attached to a garden hose are effective for liquid
applications. Remember that the higher the pressure and the
finer the mist, the more likely it is that the herbicide will
drift and injure shrubs, trees, flowers, and vegetables.
Sprinkler cans may be used on small areas, but once any
applicator has been used to apply herbicides, it should not be
used to spray other pesticides on ornamental or garden plants.
You should use a separate sprayer for killing weeds. Be sure
to clean the sprayer thoroughly after each use.
Broadleaf
Weeds
| Dandelion |
(P) |
These weeds are best controlled by
selective post-emergence herbicides. |
| Dock |
(P) |
Early fall is the best time to control
winter annual (WA) |
| Plantain |
(P) |
and perennial weeds (P.) |
| Purslane |
(P) |
Spring is the best time for summer
annual (A) weeds. |
| Thistle |
(P) |
Apply when soil is moist and weeds are
young and actively growing. |
| Black Medic |
(A) |
Dicamba can be dangerous to trees and
shrubs because |
| Chickweed |
(A or P) |
it can move through the soil and be
taken up by tree shrub roots. |
| Clover |
(P) |
|
| Ground Ivy(Creeping Charlie) |
(P) |
|
| Henbit |
(WA) |
|
| Knotweed |
(A) |
|
| Mallow |
(A or P) |
|
| Spurge |
(A) |
|
| Yarrow |
(P) |
|
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|
Grass Weeds
| Annual
bluegrass |
(A,
P) |
Use pre-emergence
herbicides. |
| Barnyardgrass |
(A) |
Apply two to three weeks prior to
expected germination of weed seeds. |
| Crabgrass |
(A) |
Some of these herbicides may injure
fine fescues or bentgrasses. |
| Foxtail |
(A) |
Most pre-emergent herbicides will harm
newly seeded grasses except siduron (Tupersan.)
|
| Goosegrass |
(A) |
These weeds can be controlled only with
nonselective herbicides. |
| Bromegrass |
(P) |
Spot treat only because herbicide will
also kill desirable grass plants. |
| Quackgrass |
(P) |
Apply when weeds are actively
growing. |
| Tall Fescue |
(P) |
|
| Creeping bentgrass |
(P) |
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