Managing Weeds In Warm-Season Lawns

Revised & pesticides updated by Joey Williamson, HGIC Horticulture Extension Agent, Clemson University, 10/14. Originally prepared by Chuck Burgess, HGIC Horticulture Extension Agent, Clemson University. New 06/04.

HGIC 2310

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Bermudagrass, centipedegrass, zoysiagrass, and St. Augustinegrass are the most popular warm season turfgrasses grown in South Carolina. Warm season refers to the fact that they prefer warm temperatures of spring and summer. In the winter months, they do not actively grow, but become dormant.

Disadvantages of Weeds

The main reason homeowners want to rid their lawn of weeds is that they are aesthetically disruptive. In other words, weeds are ugly and interrupt an otherwise uniform appearing lawn. Weeds are also fierce competitors and will rob the turf of sunlight, nutrients and moisture. Lastly, weeds have a tendency to spread rapidly. A few left uncontrolled can quickly become a problem.

Types of Weeds

Grassy vs. Broadleaf: Grassy weeds emerge from seed as a single leaf. The leaf blades are longer than they are wide and have parallel veins. An example is crabgrass or dallisgrass.

Broadleaf weeds emerge from seed with two leaves. Leaves have netlike veins and many, like dandelion or clover, have showy flowers.

Annual vs. Perennial: Annuals germinate, grow, and die within a twelve month period. Summer annuals, such as goosegrass, germinate in the spring, grow through the summer, set seed, and die at the onset of cold weather. Winter annuals, such as chickweed, germinate in the fall, grow through the winter, set seed and die as temperatures rise in early summer.

Perennials grow for two or more years. They reproduce from vegetative parts such as tubers, bulbs, rhizomes, or stolons, though some also produce seed. Perennials tend to be the most difficult to control. Examples are dallisgrass, wild garlic and nutsedge.

Proper Management

Weed control begins with proper management practices, which encourage a dense, healthy turf. A healthy turf shades the soil so that less sunlight reaches the ready-to-germinate weed seeds. A thick turf minimizes the space available for weeds to become established.

Best management practices include proper mowing, watering, fertilizing, liming, and core aeration. These are mentioned briefly here, but covered in detail in corresponding HGIC fact sheets. See HGIC 1205, Mowing Lawns, HGIC 1207, Watering Lawns, and HGIC 1201, Fertilizing Lawns.

Depending on the type, each warm season grass should be mowed at its recommended mowing height and frequently enough so that no more than ⅓ of the blade is removed. For turfgrass in partial shade, the mowing heights may be raised slightly. Mowing at the proper heights for the particular turfgrass will encourage a dense, healthy lawn.

When lawns show signs of drought stress, apply enough irrigation to deeply wet the entire root zone. Typically, water lawns with 1 inch of irrigation water per week if there is inadequate rainfall. One inch of irrigation water will wet the soil to 6 inches deep, and encourage a healthy, extensive root system. During hot dry periods and on sandy soil, irrigation may be required every three to five days. Watering more frequently (three or more times per week) will keep the soil surface moist and will promote weed seed germination.

Fertilize and lime at the proper time and according to a soil test. Proper lime application will help to maintain a soil pH where nutrients are optimally available to the turf.

Core aeration helps relieve the soil compaction that prevents optimum root growth and favors many weeds. Core aeration is superior to spike aeration.

Control with Herbicides

Even when cultural practices are heeded, weeds may appear. If the number of weeds reaches an unacceptable level and pulling by hand is out of the question, you may want to turn to herbicides. At this point, it is important to know what weed you are trying to control. Local Extension offices, the Clemson Home & Garden Information Center, the Clemson Plant Problem Clinic, and publications can aid in identification.

Preemergence Herbicides

Preemergence herbicides are applied to the soil prior to weed seed germination. They provide good control of many annual grassy weeds and are the best weapon against crabgrass. They also control some broadleaf weeds. Most are in a granular formulation; however, you may also find them as a liquid.

Most granular preemergence herbicides should be watered in with about ½ inch of irrigation immediately following application. This activates the herbicide which is absorbed by the young roots and shoots of weeds as they begin to grow.

In the spring, preemergence herbicides should be applied when air temperatures reach 65-70° F for four consecutive days. On average, this is March 1 for the coastal and central regions and March 15-30 for the piedmont and mountains. In the fall, to control winter annuals, apply preemergence herbicides when nighttime lows reach 55-60° F for four consecutive days. On average, this is September 15 thru October 1 for the coastal and central regions, and September 1-15 for the piedmont and mountains.

Preemergence herbicides are generally effective for six to 12 weeks, depending on the product. For season-long control, make a second application nine weeks after the first. See Table 1 for examples of herbicides and products.

Postemergence Herbicides

Postemergence herbicides target visible weeds. They are used primarily against broadleaf weeds, perennial grasses, and sedges. The chemicals 2,4-D, dicamba, mecoprop (MCPP), carfentrazone, and sulfentrazone are very common broadleaf herbicides for use in warm season turfgrass lawns. They have been combined in many products that control most broadleaf weeds. Often products will contain one or more of these broadleaf herbicides mixed with additional herbicides for control of grass weeds and/or sedges.

Bentazon, imazaquin and halosulfuron are sedge killers. Sethoxydim, quinclorac, fluazifop and fenoxaprop are selective grass weed killers. Sulfentrazone and carfentrazone kill broadleaf weeds and sedges. MCPA controls a wide range of broadleaf weeds, but is less commonly found in lawn herbicide mixes. Atrazine is both a broadleaf weed and grass weed killer.

Most of these postemergence herbicides can only be used on certain species of turfgrass. Read the product label to be sure it can be used safely on your type of lawn. See Table 2 for examples of herbicides and products.

Guidelines for Using Postemergence Herbicides

When choosing an herbicide, be sure that it will control the targeted weed and that it is recommended for your turf. Before using, read the entire label and follow it precisely for rate and timing. The following tips will help you achieve optimum control.

  • Most broadleaf weeds are best treated in the spring or fall when air temperatures are between 65 and 85° F. During hotter temperatures, turf damage is more likely to occur.
  • At the time of treatment, soil moisture should be adequate. When stressed by drought, weed control is poor and turf damage may occur.
  • Do not mow immediately prior to or after application. Mowing lessens the amount of herbicide that contacts weed leaf surface area.
  • Treat weeds when no rain is expected for at least 24 hours with spray applications.
  • Avoid treating on windy days because herbicide drift can injure ornamental plants.
  • Best results occur when weeds are young.
  • For acceptable control, repeat applications 10 to 14 days apart may be required.

Precautions for New Lawns

It is best to not apply any herbicides during the first year after seeding or sodding a lawn. Besides, during this first year there may be no weeds that need controlling. Simply mow and bag the clippings for any minor weed problems.

However, if weeds have become significant, postemergence herbicides can be applied to newly seeded lawns at ½ the rate, but only after it’s been mowed four times. If the lawn is to be over-seeded after a postemergence herbicide treatment, wait three to four weeks to reduce injury to the new seedlings, depending on the product. If seeding after applying a preemergence herbicide, wait at least nine weeks, but read the product label for the exact amount of time to wait after application before seeding.

In recently sodded areas, preemergence herbicides can be applied following signs of new growth, at ½ the rate recommended for established grasses. Postemergence herbicides should not be applied until the grass is visibly growing and spreading. Use ½ the recommended rate until after the turf has been mowed three times.

Calendar

February – March:
Preemergence:
Apply a preemergence herbicide (see Table 1) according to the previously mentioned dates. If rain is not expected within 48 hours, apply ½-inch of irrigation. Many preemergence herbicides do not last more than 8 or 9 weeks, so a second application may be required 60 days later.

Postemergence: Before turfgrasses begin to green up for summer growth, apply a postemergence herbicide (see Table 2) to control winter broadleaf weeds or summer broadleaf weeds that have emerged. Turf damage may occur following some broadleaf herbicide applications if used during turfgrass green-up, especially in more sensitive turfgrasses, such as centipedegrass and St Augustinegrass. If the lawn has begun to come out of dormancy, then wait until the turfgrass is totally greened up before applying a postemergence weed killer. As with any pesticide, read the label to make sure that it is appropriate for your situation, and that it is being applied at the correct rate.

May – July:
Preemergence:
If making two spring applications, apply again 60 days following the first application

Postemergence: If annual grasses such as crabgrass, or perennial grasses such as dallisgrass have emerged, apply a postemergence grass herbicide. Two to three applications, 14 to 21 days apart may be necessary for control. For broadleaf weeds, apply a three-way mixture, such as containing 2,4-D, dicamba and mecoprop. See Table 2 for examples.

August – October:
Preemergence:
Make applications according to the previously mentioned schedule, to control annual winter weeds. Most crabgrass preventers will stop most annual grass weeds from coming up in the lawn, including annual blue grass (Poa annua). However, these preemergence herbicides may need to be reapplied twice in the fall for season long control, so check the product label (see Table 1).

Postemergence: Continue to treat grassy weeds. Best control is achieved when treating young plants.

November – January:
Postemergence:
Treat winter broadleaf weeds with a postemergence herbicide on mild days. Wild onions and garlic are best treated during November and again during February using a three-way herbicide. If necessary, repeat spray application during the following November (see Table 2).

Non-selective herbicides, such as Roundup or Eraser, can be used safely on bermudagrass that is completely dormant. However, in SC, turfgrasses may not go completely dormant due to the mild winter, and glyphosate application may delay total green-up in the spots where sprayed.


Table 1. Preemergence Herbicides for Lawns.
TurfgrassWeeds PreventedActive IngredientsExamples of Brands & Products
Notes: These preemergence herbicides should only be applied to well-established turfgrass lawns.
Typically, the optimum time for lawn fertilizer applications and pre-emergence herbicide applications do not coincide. However, the small amount of potash in the 0-0-7 blends is normally not a problem, & may be useful on sandy soils with fall applications to improve cold weather hardiness of the lawn.
Bahiagrass
Bermudagrass
Centipedegrass
St. Augustinegrass
Zoysiagrass
Annual grass
weeds including
crabgrass & annual
bluegrass; also
some broadleaf
weeds
benefin Pennington Crabgrass Preventer
Same as for
benefin, plus
goosegrass
oryzalin Southern Ag Surflan A.S.
Same as above benefin +
oryzalin
XL2G
Summer annual
grasses, annual
bluegrass, some
selected annual
broadleaf weeds
benefin +
trifluralin
Anderson Turf Products Crabgrass Preventer with 2% Team Herbicide
Hi-Yield Crabgrass Control

Same as for
benefin,
plus oxalis
& speedwell

pendimethalin Scotts Halts Crabgrass Preventer
Same as for
benefin, plus
oxalis
dithiopyr Bonide Crabgrass & Weed Preventer for Lawns & Ornamental Beds
Green Light Crabgrass Preventer 2 with Dimension
Hi Yield Turf & Ornamental Weed & Grass Stopper with Dimension
StaGreen CrabEx Crabgrass Preventer
broadleaf weeds,
such as chickweed,
clover, henbit,
bittercress, spurge,
plantain, & others
isoxaben Ferti-lome Broadleaf Weed Control with Gallery
Green Light Portrait Broadleaf Weed Preventer
Bahiagrass
Bermudagrass
Centipedegrass
St. Augustinegrass
Zoysiagrass
summer annual
grasses, annual
bluegrass, some
selected weeds
such as chickweed,
spurge, goosegrass
prodiamine Helena Pro-Mate Barracade & Fertilizer 0-0-7
Howard Johnson Crabgrass Control with Prodiamine & 0-0-7
Lebanon Pro Fertilizer (0-0-7) with Prodiamine
Lesco Barricade Plus Fertilizer 0-0-7
Lesco Stonewall Plus Fertilizer (0-0-7)
Pro-Mate Barracade Plus Fertilizer (0-0-7)
Scotts Halts Pro 0-0-7 & Halts Pro

Table 2. Postemergence Herbicides for Lawns.
TurfgrassWeeds ControlledActive IngredientsExamples of Brands & Products
Do not apply postemergence herbicides to lawns during the spring green up of turfgrass.
1Intermediate safety; use at reduced rates.
2These products require the addition of 2 teaspoons of a non-ionic surfactant (that is, a wetter-sticker agent to aid in weed control at 0.25% by volume) per gallon of water, such as Hi-Yield Spreader Sticker.
3For use on common bermudagrass. Intermediate safety on hybrid bermudagrass.
Centipedegrass crabgrass,
goosegrass & other
annual grasses &
bermudagrass;
bahiagrass and
dallisgrass suppression
sethoxydim Southern Ag Vantage Grass Killer
Centipedegrass
St. Augustinegrass
clover, lespedeza,
spurge, oxalis,
dollarweed, Florida
betony & other
broadleaf weeds and
crabgrass & annual grasses
atrazine Hi Yield Atrazine Weed Killer
Image for St. Augustinegrass & Centipedegrass with Atrazine
Southern AG Atrazine St. Augustine Weed Killer
Spectracide Weed Stop for Lawns Concentrate for St. Augustine  & Centipede Lawns
Zoysiagrass1 annual & perennial
grasses, such as
crabgrass, foxtails,
goosegrass, sandbur;
bermudagrass suppression
fluazifop Syngenta Fusilade II Turf & Ornamental2
fenoxaprop Aventis Acclaim Extra 0.57EC2
Bahiagrass
Bermudagrass
Centipedegrass
St. Augustinegrass
Zoysiagrass
wild garlic, wild
onion, dandelion,
clover, plantains,
and most other
broadleaf weeds
2, 4-D +
dicamba +
mecoprop (MCPP)
Bayer Advanced Southern Weed Killer For Lawns
Bonide Weed Beater Lawn Weed Killer with Trimec
Bonide Lawn Weed Killer Granules
Ferti-lome Weed Out Lawn Weed Killer With Trimec
Lilly Miller Lawn Weed Killer
Southern Ag Lawn Weed Killer with Trimec Conc.
Bahiagrass
Bermudagrass
Centipedegrass
St. Augustinegrass
Zoysiagrass
wild garlic, wild
onion, dandelion,
clover, plantains,
and most other
broadleaf weeds,
plus sedges
2,4-D +
dicamba +
mecoprop (MCPP) + sulfentrazone
Spectracide Weed Stop Weed Killer For Lawns
Bermudagrass
Centipedegrass
St. Augustinegrass
Zoysiagrass
wild garlic, wild
onion, dandelion,
clover, plantains,
and most other
broadleaf weeds;
& moss suppression
2,4-D +
dicamba +
mecoprop +
(MCPP) +
carfentrazone
Bonide Weed Beater Ultra Concentrate
Ortho Weed B Gon Max for Southern Lawns
Bermudagrass3
Zoysiagrass

crabgrass, foxtails,
signalgrass; most
broadleaf weeds,
such as dollarweed,
black medic, wild
onion & garlic,
speedwells,
plantains, dandelion,
white clover, violets,
henbit, chickweed,
star of Bethlehem

2,4-D +
dicamba +
quinclorac
Bayer Advanced All-in-One Lawn Weed & Crabgrass Killer Conc.
Ferti-lome Weed Out with Q Concentrate
Green Light Wipe Out Crabgrass Killer Plus Concentrate
Monterey Crab-E-Rad Plus Concentrate
Ortho Weed B Gon Max Plus Crabgrass Control Concentrate
Bermudagrass3
Zoysiagrass
crabgrass, foxtails,
signalgrass; most
broadleaf weeds,
such as dollarweed,
black medic, speedwells,
plantains, dandelion,
white clover, violets,
henbit, chickweed,
star of Bethlehem, & nutsedges.
2,4-D +
dicamba +
quinclorac +
sulfentrazone
Spectracide Weed Stop for Lawns Plus Crabgrass Killer Conc.
Bermudagrass3
Zoysiagrass
crabgrass, foxtails,
signalgrass; some
broadleaf weeds,
such as dollarweed,
black medic,
speedwells, dandelion,
white clover, violets,
henbit, chickweed,
star of Bethlehem, & nutsedges.
sulfentrazone +
quinclorac
Image Kills Crabgrass Concentrate
Bahiagrass
Bermudagrass
Zoysiagrass
many broadleaf
weeds; partial
bermudagrass
suppression
2,4-D +
dicamba +
triclopyr
Ortho Weed B Gon Max Weed Killer for Lawns Concentrate
Bahiagrass
Bermudagrass
Zoysiagrass
many broadleaf
weeds; partial
bermudagrass
suppression
MCPA +
dicamba +
triclopyr
Monterey Spurge Power Concentrate
Bahiagrass
Bermudagrass Centipedegrass
St. Augustinegrass
Zoysiagrass
yellow nutsedge,
globe sedge, annual
sedge, and
many broadleaf weeds
bentazon BASF Basagran T & O 4L
Lesco LescoGran Postemergence Herbicide
Southern Ag Basagran Sedge Control
Bahiagrass
Bermudagrass Centipedegrass
St. Augustinegrass
Zoysiagrass
yellow & purple nutsedge,
annual sedges, common
purslane, groundsel
halosulfuron Gowen SedgeHammer2
Monterey Nutgrass Killer2
Hi-Yield Nutsedge Control2
Bermudagrass1
Centipedegrass1
St. Augustinegrass1
Zoysiagrass
purple nutsedge,
annual sedges,
sandspur, wild garlic,
and some broadleaf
weeds
imazaquin Image Nutsedge Killer

Table 3. Preemergence & Postemergence Herbicide Combination Products for Lawns.
TurfgrassWeeds ControlledActive IngredientsExamples of Brands & Products
Note: These preemergence herbicides should only be applied to well-established turfgrass lawns.
Bahiagrass
Bermudagrass
Centipedegrass
St. Augustinegrass
Zoysiagrass
Preemergence:
summer annual
grasses (such as
crabgrass & goosegrass),
annual bluegrass, & some
broadleaf weeds, such as
chickweed & spurge.
Postemergence: most
perennial & annual sedges,
many broadleaf weeds &
some annual bluegrass control.
prodiamine (pre)
+
sulfentrazone (post)
Bonide Weed Beater Complete Granules
Bonide Sedge Ender Concentrate
Bahiagrass
Bermudagrass,
Centipedegrass,
St. Augustinegrass,
Zoysiagrass
Preemergence:
broadleaf weeds,
such as chickweed,
clover, henbit,
bittercress, spurge,
plantain & others.
Postemergence:
most broadleaf weeds.
isoxaben (pre)
+
(post)
2,4-D +
dicamba +
mecoprop (MCPP)
Bayer Advanced Season Long Weed Control for Lawns, or
Bayer Advanced Southern Season Long Weed Control for Lawns

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This information is supplied with the understanding that no discrimination is intended and no endorsement of brand names or registered trademarks by the Clemson University Cooperative Extension Service is implied, nor is any discrimination intended by the exclusion of products or manufacturers not named. All recommendations are for South Carolina conditions and may not apply to other areas. Use pesticides only according to the directions on the label. All recommendations for pesticide use are for South Carolina only and were legal at the time of publication, but the status of registration and use patterns are subject to change by action of state and federal regulatory agencies. Follow all directions, precautions and restrictions that are listed.