Home Lawn Weed Control
Brad S. Fresenburg
Department of Horticulture
Weed-free turf beautifies and adds greater usefulness to home landscapes, recreational areas, and public and industrial grounds. Proper management is the most effective factor in weed control, but unfavorable climate, insects, diseases or abuse permits weeds to invade your lawn. Under such conditions, careful use of appropriate herbicides permits the turf to recover its original value. Figure 1 shows identifying characteristics of a number of weeds frequently found in lawns (crabgrass and dandelion are omitted because they are well known).
Weed control principles
A dense stand of healthy grass provides the best weed control. Because most weeds are “opportunists” that invade weakened lawns, the fight against weeds starts with good turf management. Cultural practices such as mowing, fertilizing and watering should be done in a manner and time that will favor the grass rather than the weeds. Height of mowing influences competition against weeds such as crabgrass -- the higher the cut, the lower the infestation. Frequent light sprinkling encourages shallow-rooted weeds and seed germination. Less frequent “deep-soak” watering that maintains a dry surface layer provides the grass with a competitive advantage.
Temperature, light, soil moisture and other factors determine the time and extent of weed germination and development. Some weeds germinate in early spring while others sprout in summer or fall. If conditions are favorable, a weed may be particularly abundant in a given year, but under different conditions the next year, it may be little in evidence.
Weeds that germinate in the spring from seed and mature in summer or fall each year (crabgrass and knotweed, for example), are designated as summer annuals. Chickweed, henbit and others germinate in fall or late winter and mature in late spring. These are called winter annuals.
Preemergence herbicides (chemicals applied before germination of weed seeds) must be applied in spring to control summer annuals, but in fall to control winter annuals (Tables 1 and 2). After weeds appear, postemergence herbicides must be used.
Perennial broadleaf weeds live more than two years but may produce seeds for new plants each year. Like biennials, which require two years to complete a life cycle, they store food in fleshy roots for next year’s growth. Generally, postemergence herbicides are required for control of biennials and are more effective during the first year’s growth. Fall often may be a good time to apply such herbicides (Table 1).
Herbicide application
Although most herbicides are formulated with reliable safety factors, application rates higher than those recommended may cause injury to turf and ornamental plants. Many people overapply herbicides, especially when using fertilizer-herbicide combinations. The user needs to follow instructions on containers carefully to avoid overdoses.
Preemergence treatments are applied before weeds sprout from seeds. Apply two weeks ahead of germination. Less effective control may be expected if applied more than a month before germination. Applications should not be made until excess lawn clippings and leaf litter are removed. Homeowners will find many over-the-counter preemergence products at local garden centers for control of summer annual weeds. Many are often referred to as “crabgrass preventor.” These products should be applied by April 15 in the northern half of Missouri; by April 1 in the southern half. Be sure to follow label recommendations for application rates and irrigation requirements. Crabgrass preventors, for control of summer annual grasses, require irrigation or rainfall to activate.
Postemergence herbicides containing such materials as 2,4-D, MCPP, dicamba, triclopyr, MCPA and dithiopyr are applied after weeds appear. Liquid sprays can be more effective than dry materials, especially on hard-to-kill weeds. Apply postemergence materials when weeds are growing vigorously. Tough, old weeds are hard to kill, and if mature seeds are already formed, the lawn is likely to be infested again next year. Amine forms are safest because they give off fewer vapors that might damage other plants. Volatile ester formulations should not be used around ornamental plants. However, many granular products now have formulations that offer excellent control of target weeds. Select a time when winds are calm to prevent spray drift. Using granules impregnated with herbicides near ornamentals will minimize such hazards.
Fertilizer-herbicide combinations are extremely popular because they combine two operations. Combinations with preemergence chemicals are generally effective since both fertilizer and herbicide action are dependent on contact with the soil (requiring rainfall or irrigation). Postemergence herbicide action depends more on absorption by leaves, and granules in such combinations do not adhere well to smooth-surfaced leaves. They will stick better if applied when weed leaves are damp, perhaps with morning dew. “Weed and feed” materials present a conflict in desirable actions. Proper time for weed control often does not coincide with the most desirable time and rates for fertilizing. If used for follow-up fertilizations, there is danger of herbicide overdose.
Equipment
Fertilizer spreaders can be used for applying granular herbicides. Be sure to adjust the spreader to apply recommended rates. If possible, apply half the desired rate in one direction and the remaining half at right angles to the first application.
Gravity flow applicators, compressed-air sprayers or types attached to a garden hose are effective for liquid applications. High pressures cause mists subject to drift and should be avoided. Sprinkler cans or sprinkler nozzles attached to a gallon container can be used on small areas.
A sprayer used for application of 2,4-D and related chemicals should not be used to spray garden or flower plants. Cleaning procedures are not always reliable. To be safe, have a separate sprayer for weed-killing purposes.
Eliminating weeds is of little value unless enough desirable grass is present to fill in bare spots. A reseeding program deserves first consideration if the turf is so weak that it will not recover once weeds are eliminated. Study soil and other conditions to determine reasons for low vigor of the original turf.
Note
The University of Missouri intends no endorsement.
Table 1
Chemical control of broadleaf weeds
Annual broadleaf weeds
Winter annuals
Can be controlled with Gallery preemergence herbicide applied in late September or with a three-way premix postemergence herbicide applied in late fall or early spring on a warm day.
- Common chickweed
- Deadnettle
- Henbit
- Peppergrass
- Shepherd's-purse
Summer annuals
Knotweed and speedwell germinate very early in the spring. Mallow is a biennial weed. Black medic and yellow wood sorrel can be perennials. Applications should be made early in the weeds' development for best control.
- Black medic
- Carpetweed
- Knotweed
- Kochia
- Lambsquarters
- Mallow
- Pigweed
- Puncturevine
- Purslane
- Ragweed
- Speedwell (Veronica)
- Spurge, spotted
- Vervain
- Yellow wood sorrel
Annual broadleaf herbicides
Trade name/common name
Preemergence
Postemergence
- Cool Power/MCPA + triclopyr + dicamba
- Dissolve/2,4-D + MCPP + dichlorprop
- Horsepower/MCPA + triclopyr + dicamba
- Power Zone/carfentrazone + MCPA + MCPP + dicamba
- Speed Zone/carfentrazone + 2,4-D ester + MCPP + dicamba
- Super Trimec/2,4-D + 2,4-DP + dicamba
- Three-Way/2,4-D + MCPP + dicamba
- Triamine/2,4-D + MCPP + dichlorprop
- Trimec Classic/2,4-D + MCPP + dicamba
- Triplet/2,4-D + MCPP + dicamba
- Tri-Power/MCPA + MCPP + dicamba
- Turflon II Amine/2,4-D + triclopyr (amine formulation)
- Turflon Ester/triclopyr ester
- Weed-B-Gon/2,4-D + MCPP + dicamba
Preemergence herbicides for annual grass control will provide preemergence control of many winter and summer annual broadleaf weeds. Apply in the spring for summer annuals; early fall for winter annuals. Please refer to the labels for information.
Perennial broadleaf weeds
Applications in the spring or fall while weeds are active will give control. Best control is achieved in the fall when weeds are translocating food reserves from tops to roots in preparation for winter.
Perennial broadleaf herbicides
Trade name/common name
Postemergence
- Cool Power/MCPA + triclopyr + dicamba
- Dissolve/2,4-D + MCPP + dichlorprop
- Horsepower/MCPA + triclopyr + dicamba
- Power Zone/carfentrazone + MCPA + MCPP + dicamba
- Speed Zone/carfentrazone + 2,4-D ester + MCPP + dicamba
- Super Trimec/2,4-D + 2,4-DP + dicamba
- Three-Way/2,4-D + MCPP + dicamba
- Triamine/2,4-D + MCPP + dichlorprop
- Trimec Classic/2,4-D + MCPP + dicamba
- Triplet/2,4-D + MCPP + dicamba
- Tri-Power/MCPA + MCPP + dicamba
- Turflon Ester/triclopyr ester
- Weed-B-Gon MAX/triclopyr+ MCPP + dicamba
Advantages of fall applications of postemergence broadleaf herbicides
- Less risk of injury to desired plants.
- Both perennial and winter annual seedlings can be controlled.
- Perennials weakened by herbicide may be killed by winter weather.
- Bare spots left by dead weeds will be filled sooner by bluegrass and other cool-season grasses.
Note
Postemergence herbicides containing dicamba can damage ornamental trees, shrubs and flowers. Use label recommendations and precautions when ornamentals are in the area.
Note
Always read container label before pesticide use and apply only as directed. To use product in any way that is inconsistent with the label is a violation of the Federal Environmental Pesticide Control Act of 1972.
Table 2
Chemical control of grasses and miscellaneous weeds.
Annual grass weeds
Winter annual
Annual bluegrass does not compete with dense, well-maintained lawns.
Summer annuals
Preemergence applications should be made by April 1in southern Missouri and April 15 in central and northern Missouri. Preemergence herbicides should be watered in for best results. Postemergence herbicides should be applied when annual grasses are in a 1- to 3-leaf stage for best control. Make sure the desirable grass species is not under stress. Note any temperature restrictions on the label.
Annual grass herbicides
Trade name/common name
Preemergence
- Balan/benefin
- Barricade/ prodiamine
- Dimension/dithiopyr
- Pendulum/pendimethalin
- Pre-M/pendimethalin
- Ronstar/oxidiazon
- Team/benefin + trifluralin
- Tupersan/siduron
- Weedgrass Control/pendimethalin
Postemergence
- Acclaim Extra/fenoxaprop-ethyl
- Dimension/dithiopyr
- Drive/quinclorac
Perennial grass weeds
Nonselective herbicides can be used as a spot treatment to kill patches of perennial grasses before renovating to a desirable grass species. Corsair is available to control tall fescue in Kentucky bluegrass. Revolver will control bluegrass, ryegrass and tall fescue in zoysiagrass and bermudagrass.
Perennial grass herbicides
Trade name/common name
- Corsair/chlorsulfuron
- Finale/glyfosinate-ammonium
- Quik Pro/diquat + glyphosate
- Roundup Pro/glyphosate
- Revolver/foramsulfuron
- Scythe/pelargonic acid
Miscellaneous weeds herbicides
Trade name/common name
- Algae and moss
Usually grows when conditions are unsuitable for desirable grass species. Causes include soil compaction, excess moisture and shade, acid soils, low fertility. Correction of cause often eliminates moss. Apply lime regularly, aerify and improve soil drainage, air circulation and sunlight.
- Wild garlic
Use low volatile 2,4-D esters in combination with dicamba. Several applications may be required.
- Vanquish + 2,4-D Ester/dicamba + 2,4-D ester
- 2,4-D Ester/2,4-D ester
- Yellow nutsedge
Repeat applications will be required for some herbicides. Make sure desirable grass species are not under stress. Note any temperature restrictions on the label. Yellow nutsedge does not compete well with dense, well-maintained lawns.
- Basagran T-O/bentazon
- Sedgehammer/halosulfuron-methyl-5
G6750, revised October 2006