Volume XXIX |
By Tim R. Murphy
University of Georgia
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.
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.)
