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By Tim R. Murphy
University of Georgia
Weed control in lawns is more than just using a herbicide. If you
want a high-quality, aesthetically appealing lawn, you’ll need an
integrated weed management strategy.
IWM plans use preventive, cultural, mechanical and chemical means
to control weeds in home lawns. Putting them together in an
overall plan involves five parts.
1. Scout the lawn and identify problem
weeds. Since some species infest lawns only in certain
times of the year, scout at least twice per year.
Scout for winter annual weeds in December to early February.
Winter annuals are small then, and you can easily kill them with
postemergence herbicides. For the same reason, scout for summer
annuals such as crabgrass in late April to July.
It’s good to scout in late summer and fall, too, to see how
effective the summer weed control has been. And scout in late
spring to see how well the winter program worked.
Scouting isn’t hard. You do have to keep accurate records of
where the weeds are, so you can decide how to best manage them.
Do this by drawing a representative map of the lawn.
Scout the lawn by walking or riding over the area. Most people
zigzag with random stops along the way. At each stop, record the
weed species and their density. Mark them as low density (1
percent to 10 percent of the plants), medium (11 percent to 20
percent) or high (more than 20 percent).
There aren’t any set thresholds for weeds in turf. A low density
could be fine to some people, while the same density level would
be unthinkable to others.
2. Know the life cycle of weeds you
find. Identification references usually list the weed’s
life cycle. If it’s an annual, you may be able to use a
preemergence herbicide for control. If it’s a perennial such as
dandelion, you’ll have to use a postemergence herbicide.
3. Record any problems you find.
This may include thin turf caused by disease or insects, drainage
problems, drought, incorrect mowing height or frequency,
nonadapted turf species, compacted soils, shade, mechanical
damage or not enough mulch cover.
Weeds often indicate soil, management and environmental problems.
For example:
- Finding sedges (perennial kyllinga, purple nutsedge, annual
sedges) may mean the site is too wet, either from overwatering or
poor drainage. - Drought-tolerant weeds such as pink purslane, annual
lespedeza and goosegrass can be a sign that you need to water
more. - Certain weeds such as annual bluegrass, prostrate knotweed
and broadleaf plantain thrive in compacted soils. - Mowing the grass too short will favor weeds such as annual
bluegrass, common chickweed, crabgrass and dandelion. - A high weed population in dense shade may mean there isn’t
enough sunlight for the grass.
Be sure you correct these problems. That will enable the turf to
properly grow and compete with weeds.
4. Develop a good control program for
problem weeds. Use whatever methods — preventive,
cultural, mechanical and chemical — will help control the weeds.
If moisture-loving weeds are a problem, correct the irrigation or
soil drainage as part of an IWM plan that uses labeled
herbicides, too. Check the success of this two-phase program at
times after you start the plan.
5. Properly maintain the turf. The
first line of defense against weeds has always been, and probably
always will be, a thick, healthy, properly maintained turf.
Maintain proper soil fertility and pH levels. Irrigate properly.
Control other pests. Mow at the correct height and frequency for
the turf species. These practices will make most chemical weed
control programs more effective.
IWM doesn’t mean eliminating herbicides. In fact, you may even
use more in the first few years as your scouting finds other
problem weeds. Over time, though, using a proper IWM plan should
lead to using fewer herbicides.
(Tim Murphy is an Extension Service weed scientist with the
University of Georgia College of Agricultural and Environmental
Sciences.)
