Crabgrass

Pest Notes: Introduction

Crabgrass is a common weed in California lawns and landscapes, often mistaken for other grassy weeds. Two different species occur: small or smooth crabgrass, Digitaria ischaemum, and large or hairy crabgrass, D. sanguinalis. These weedy grasses are summer annuals that grow from seed each year. Crabgrass seeds germinate when soil temperatures warm in the spring, and plants typically die with the first frost in the fall. However, in some parts of California where winters are mild, the plants may live longer.

Crabgrass grows in most parts of California, except at high elevations and areas that receive no summer water. Smooth crabgrass is most often found in lawns, ornamental landscapes, and vegetable gardens. Large crabgrass can be a residential weed but also grows in orchards, vineyards, and other agricultural areas. Both species are common in vacant lots, roadsides, and other non-cultivated or natural areas. Crabgrass has many other names including crowfoot grass, fingergrass, and summer grass. It is often confused with goosegrass and the perennial weeds dallisgrass and bermudagrass.

Identification and Biology

For a quick and easy reference guide, see Grass Identification Characteristics.

Smooth Crabgrass

Smooth crabgrass is a low-growing weed. It spreads primarily by seed but also from rooting at nodes along the stem that lie on the soil. Unmowed, it will grow upright to about 6 inches, but even when mowed to a height as short as 1/2 inch, it can still produce seed. Crabgrass often forms patches in lawns, and plants can grow together to form large clumps.

Seedling leaves are light green and smooth. These pale leaves are easy to spot in established lawns. Mature leaves are usually darker green, but still smoother and paler in color than most desirable turfgrasses. The leaf blade is 1/4 to 1/3 inch wide, up to 5 inches long, and pointed at the tip. At the base of the leaf blade is a membranous projection known as the ligule. The collar region between the leaf blade and the leaf sheath lacks the clasping, prominent outgrowths (auricle) present on some grasses. The leaf sheath and upper leaf surface are smooth, but a few hairs can be present on the lower leaf surface. Sometimes a reddish tint is visible at the base of the leaf.

The inflorescence, or flower stalk, has 5 to 7 fingerlike spikes or branches that originate from the main stem at 1/8 to 1/4-inch intervals. The branches are 1/2 to 2 1/2 inches long at the end of the stalk.

Large Crabgrass

When found in turf, large crabgrass is low-growing and spreads by seed as well as from rooting at stem nodes that are in contact with the soil. Unmowed, it can grow up to 2 feet tall. It doesn’t tolerate close mowing as well as smooth crabgrass and is less common in turf situations.

Large crabgrass seedling leaves are light green and hairy. True leaves are slightly darker than the seedling leaves. They are generally 3 inches long and hairy on the upper and lower surfaces of the leaf blade and sheath. The collar region and flower stalk are similar to smooth crabgrass, but the 3 to 11 fingerlike branches are longer (about 2 to 5 inches) at the end of the stalk. Seed production from a single, large crabgrass plant can exceed 100,000 seeds.

Germination Periods

Both species of crabgrass start to germinate when soil temperatures reach 55°F for several consecutive days, providing there is adequate soil moisture. In southern coastal California where the winters and summers are relatively mild, the major germination period is extended from mid-January to early April, and seedlings continue to emerge throughout spring and summer. Crabgrass development is slow in this mild climate, and flowering may begin as late as July or August. Although classified as an annual species, in the absence of a killing frost, crabgrass can sometimes overwinter and resume growth the following spring.

In Southern California’s inland valleys, crabgrass germination and growth occur during mid-February to early April, and plants die with the first frost.

In the Central Valley and Central Coast, crabgrass begins to sprout in early February to mid-March. Growth and germination of new seeds may then continue throughout summer and into fall. Plants die with the first frost and freezing temperatures, typically in late October.

In Northern California and the North Coast, crabgrass germination usually starts later than in other parts of the state, from late February to mid-March. The growing season is also shorter, since crabgrass dies in response to the first frost, which typically occurs earlier than in Central California.

In all parts of the state, germination may occur earlier near warm surfaces such as buildings and pavement; this early germination can be a good indicator that the main germination period for the area is about to begin.

Distinguishing Crabgrass from Other Grasses

The flowering stalks of both species of crabgrass are similar to those of bermudagrass and goosegrass. The fingerlike branches on the flowering stems on crabgrass originate about 1/8 to 1/4 inch apart at the end of the stem and are usually longer than bermudagrass or goosegrass. The branches on the flowering stems of these other grasses originate at the same point.

Dallisgrass, another common grass weed in lawns, has fingerlike branches that are widely separated on the flowering stem. Dallisgrass and bermudagrass can also be readily distinguished from crabgrass by their characteristic vegetative reproductive structures that allow rapid spread in the garden. Dallisgrass has short, thick, underground rhizomes. Bermudagrass spreads with slender, belowground rhizomes and aboveground rooting stems called stolons. As an annual weed, crabgrass spreads primarily by seed and doesn’t have rhizomes or stolons.

Management

Crabgrass can be effectively managed using a variety of cultural and chemical control tactics. Controlling crabgrass before it sets seed is very important because crabgrass produces a large number of seeds, which can remain viable for at least 3 years in soil.

Cultural Control in Turfgrass

Cultural controls are gardening practices that prevent or reduce the establishment, reproduction, dispersal, and survival of insect, disease, or weed pests and at the same time, favor the growth and vigor of the turfgrass. Any cultural efforts that reduce seed production and introduction of new seed will limit crabgrass since it spreads by seed.

Cultural practices include selecting and growing the best turf species for your area, using the proper mowing height for your specific turf, applying fertilizer at the correct time of year, applying the right amount of water at the appropriate frequency, and in some locales and situations, overseeding to keep turfgrass thick. For more specific and detailed information on maintaining vigorous lawns that out compete weeds, refer to The UC Guide to Healthy Lawns. This easy-to-follow guide provides useful information on home lawn care that leads to growing a healthy, vigorous, dense turf.

Turfgrass Species Selection

Selecting a turfgrass that is adapted to your local conditions will help produce vigorous turf and prevent weeds from establishing. Turfgrass species vary in their tolerance to extreme temperatures, shade, drought, and amount of wear. They are divided into two broad categories: cool-season and warm-season grasses. Cool-season turfgrass species (bentgrass, Kentucky bluegrass, tall fescue, and ryegrass) are most competitive with weeds in coastal and northern regions of California. Warm-season species (such as bermudagrass, buffalograss, St. Augustine, and zoysiagrass) are most competitive with weeds in interior valleys and desert regions. Kikuyugrass is a coarse, warm-season turfgrass with a specific niche in south coastal regions, but for most areas of California it is considered a weed and an undesirable turf species. Seashore paspalum also has a specific niche in saline areas of Southern California. 

Both cool-season and warm-season turf species are used throughout California. Select varieties that are more drought tolerant. Newer cultivars of all of these turfgrass species are tested and compared throughout the country each year. Seed and sod producers select the cultivars that are better adapted to biotic and abiotic stresses and require fewer overall inputs to maintain. Try to select and grow these new cultivars when establishing or renovating turfgrass areas. Consult with your local nursery, sod producer, or landscape professional for more information on the best species and cultivars for your geographic area. Also, in the turf selection process, it is important to consider the amount of foot traffic, pest problems, and shade, as these factors can significantly impact the vigor of the lawn. For example, hybrid bermudagrass can be very competitive, but only if it receives adequate sunlight. If it receives fewer than 6 hours of sun during the day, it will grow poorly, and weeds can easily invade.

Mowing Height and Frequency

Mowing at the optimum height for your lawn type increases turfgrass vigor and reduces the germination and establishment of crabgrass. Optimum mowing heights differ for each turfgrass species (Table 1). Mowing too short and too often can lead to bare spots and thin patches in the lawn, which then allows weed seeds to germinate and invade. Mowing frequency depends upon how fast the lawn is growing, but the general rule is to only remove about one-third of the leaf surface. Therefore the mowing schedule should change with the season. After mowing crabgrass-infested turf, thoroughly clean the mower to remove seeds and avoid transferring them to non-infested sites.

Table 1A: Recommended Mowing Heights of Common Cool Season Turfgrass Species.

Cool Season Grasses	Mowing Height Inches
Creeping Bentgrass	< 0.5
Kentucky Bluegrass	1.5–3.0
Tall Fescue	2.0–3.0
Annual Ryegrass	1.0–3.0
Perennial Ryegrass	1.0–3.0

Table 1B: Recommended Mowing Heights of Common Warm Season Turfgrass Species.

Warm Season Grasses	Mowing Height Inches
Common Bermudagrass	1.0–2.0
Hybrid Bermudagrass	1.0–2.0
Buffalograss	2.0–unmowed
Kikuyugrass	1.0–2.0
Seashore Paspalum	1.0–2.0
St. Augustinegrass	2.0–3.0
Zoysiagrass	1.0–2.0

Fertilization

Fertilizers can increase turfgrass vigor, and a dense lawn reduces the possibility of a crabgrass invasion. The best time to fertilize is when the turf is actively growing, which depends upon turf species and local weather conditions. Because seedling crabgrass isn’t very competitive, a vigorously growing turf will crowd out new seedlings. In contrast, an underfertilized, weak lawn has a greater chance of being invaded by weeds. In general, most lawns need 4 to 6 pounds of actual nitrogen per 1000 square feet divided into 4 to 6 applications per year. A complete fertilizer containing nitrogen, phosphorus, and potassium is recommended at least once a year, usually in spring.   

Water Management

Irrigation timing and amount can affect crabgrass germination and growth. Crabgrass thrives and is often a problem in overirrigated lawns. Overwatered turf or turf that receives daily, light irrigation encourages shallow root growth making the turfgrass weaker and more vulnerable to stress during periods of heat and drought. This leads to thin patches and bare spots and to possible crabgrass invasion. Irrigating lawns deeply (to a depth of 6 to 8 inches) and less frequently allows the lawn to develop deeper roots, improving turf vigor and density.

Often, crabgrass first appears in open areas with no turf, along sidewalks where the soil can be warmer, or around sprinkler heads where turf is mowed more closely. Repair any weak or bare spots in the lawn by overseeding or transplanting plugs so the turfgrass can fill in and recover its density. This will help prevent crabgrass and other weeds from invading.

Cultural Control in the Landscape and Garden

In ornamental landscape beds, crabgrass is easily controlled by hand pulling and hoeing followed by mulching when the crabgrass plants are young and before they set seed. Solarization prior to planting or replanting is another useful tool for killing crabgrass seeds in the soil. Several chemical herbicides are available but often will not be necessary.

Mulch

Mulching with wood products (like wood chips or nuggets), composted yard waste, or synthetic landscape fabrics covered with mulch will reduce crabgrass in raised beds, landscaped areas, and around trees by blocking sunlight needed for its germination, establishment, and growth. Mulch depth depends on the size of the particles; coarse mulch might need to be 3 to 6 inches deep to control weeds, while finer mulch might need to be only 2 to 3 inches deep. Plan to replenish landscape mulches periodically because of decomposition, movement, or settling.

Be aware that organic mulches that have been on the soil for extended periods of time are slowly decomposing and they can develop into an adequate growth medium for the germination and growth of weeds. If crabgrass is germinating in the mulch, move it about with a rake or scuffle hoe to reduce seedling establishment. Hand pull established crabgrass plants before they set seed. Flaming with a handheld burner will control crabgrass seedlings but be careful not to set fire to the mulch if it is wood chips, compost, or another flammable material. For more information about mulches in landscapes, especially regarding weed control, see Pest Notes: Weed Management in Landscapes.

Solarization

Soil solarization with clear plastic (a 4 to 6 week process) prior to planting is effective for eradicating crabgrass plants and seed if you apply it during periods of high solar radiation. For more information about this process, see Pest Notes: Soil Solarization for Gardens & Landscapes.

Chemical Control

Crabgrass can be controlled in both turfgrass and ornamental beds with preemergence herbicides (applied before the weed seed germinates) or postemergence herbicides (applied after weeds germinates and emerges). Avoid using herbicides in vegetable gardens because crops grown and planted there could also be damaged. Read the label to make sure the product is safe to use on your turf type and ornamentals in the location you intend to use it. Postemergence herbicide selection and efficacy will depend on the crabgrass growth stage, and herbicide labels will include detailed guidelines on use. For help on how to find information on a pesticide label, see the “Reading a Pesticide Label” page. See Tables 2 and 3 for a partial list of herbicides available at the time this fact sheet was published.

Herbicides for Residential Turfgrass Sites

Preemergence Herbicides

There are many preemergence herbicides available for home gardeners and licensed professional applicators for crabgrass control in cool and warm-season turfgrasses (Table 2). The keys to successful crabgrass control in lawns with herbicides are application timing, uniform application of the herbicide, and uniform distribution of water to incorporate and activate the herbicide.

Preemergence herbicides generally affect plants during seed germination or the earliest growth stage. Therefore, they should be applied a few weeks before crabgrass typically germinates in your geographic area. Most preemergence herbicides need to be irrigated into the soil with about ½ inch of water soon after the herbicide application in order to be effective on weed seed germination and emergence. Applications can be timed with upcoming rain events. Be aware that any reseeding or overseeding of the turfgrass will need to be postponed until the preemergence herbicide is no longer effective. The label will indicate that time frame. In many areas of California, crabgrass germinates and grows for 6 to 8 months. A second application of a preemergence herbicide may be necessary for extended crabgrass control.

Some products (often called “weed and feed”) combine fertilizer with a preemergence herbicide so spring fertilization and preemergent treatments can be accomplished at the same time. While these products may be convenient to use, be aware that the timing for maximum crabgrass control will depend on local crabgrass germination which may not align with optimum fertilization timing.

Table 2A: Preemergence Herbicides to Prevent Crabgrass Seedling Growth in Residential Turfgrass. This is a partial listing of some common herbicide products. Always read the label to be sure the product is safe to use on your specific site.

Active Ingredient	Trade Names	General Public Use	Licensed Professional Use
benefin + oryzalin	Amaze Grass & Weed Preventer 3	Yes	No
benefin + oryzalin	Surflan XL 2G	No	Yes
bensulide	Bensumec, Betasan	No	Yes
dimethenamid	Tower	No	Yes
dithiopyr*	Dimension	No	Yes
	“Crabgrass & Spurge Preventers” (available from manufacturers such as Jonathan Green, Preen, Scotts, Spectracide, Vigoro)	Yes	No
indaziflam*	Specticle	No	Yes
mesotrione*	Tenacity	No	Yes
oryzalin	Surflan	No	Yes
pendimethalin	Pre-M, Pendulum 3.3 EC & 2G	No	Yes
pendimethalin	Scotts Halts Crabgrass & Grassy Weed Preventer, Scotts Weed-Ex, Scotts Turf Builder Halts Crabgrass Preventer	Yes	No
prodiamine	Barricade, Prodiamine 65WG	No	Yes
prodiamine	Crab Ex-Plus (Sta-Green)	Yes	No
sulfentrazone*	Dismiss CA	No	Yes

*These herbicides are primarily preemergence herbicides, but they have some postemergence activity on young crabgrass seedlings.

Table 2B: Preemergence Herbicides to Prevent Crabgrass Seedling Growth in Ornamental Beds and Landscapes. This is a partial listing of some common herbicide products. Always read the label to be sure the product is safe to use on your specific site.

Active Ingredient	Trade Names	General Public Use	Licensed Professional Use
benefin + oryzalin	Amaze Grass & Weed Preventer 3	Yes	No
benefin + oryzalin	Surflan XL 2G	No	Yes
napropamide	Devrinol	No	Yes
oryzalin	Surflan	No	Yes
oryzalin + trifluralin	Vegetable & Ornamental Weeder, Preen Garden Weed Preventer	Yes	No
trifluralin	Treflan HFP	No	Yes
trifluralin + isoxaben	Preen Extended Control Weed Preventer	Yes	No

Postemergence Herbicides

The optimum application period for postemergence herbicides is when crabgrass is small and actively growing but before it flowers and starts to set seed. It is difficult to find herbicides that selectively remove grass weeds growing in a grass lawn without damaging the lawn. Therefore only a few postemergence herbicides are available for crabgrass control in lawns (Table 3) and they are often combined with broadleaf weed killers (such as 2,4-D, MCPP, and dicamba).

Dithiopyr, indaziflam, mesotrione, and sulfentrazone are primarily preemergence herbicides, but they have some postemergence weed control activity when applied to crabgrass seedlings with less than five leaves. They are not effective at killing established crabgrass plants.

Quinclorac is often sold in a ready-to-use spray bottle for the general public, whereas professional applicators can use a more concentrated product. In either case, crabgrass control is only partial, and some crabgrass populations have shown resistance to this product.

Topramezone is a postemergence herbicide that controls broadleaf and grass weeds including crabgrass, but it cannot be used on all turf species or injury will result. Topramezone is safe to use in most cool-season turfgrasses, but many warm-season grass species are intolerant, so be sure to consult the label. Soon after a topramezone application, the treated weeds will turn white due to chlorophyll loss. Growth then stops, and weeds die. Combining quinclorac with topramezone improves postemergence crabgrass control, but as mentioned, topramezone cannot be used in all turf species.

Most postemergence herbicides will require the addition of a surfactant in the spray tank to enhance the spreading or sticking power of the spray on leaves and stems. Ready-to-use formulations will not usually require surfactants.

Table 3A: Postemergence Herbicides to Control Emerged Crabgrass in Residential Turfgrass.

Active Ingredient	Trade Names	General Public Use	Licensed Professional Use
dithiopyr*	Dimension	No	Yes
dithiopyr*	“Crabgrass & Spurge Preventers” (available from manufacturers such as Jonathan Green, Preen, Scotts, Spectracide, Vigoro)	Yes	No
indaziflam*	Specticle	No	Yes
mesotrione*	Tenacity	No	Yes
quinclorac**	Bio-Advanced All-in-One Lawn Weed & Crabgrass Killer, CrabERad Plus, Ortho Weed Clear, RoundUp for Lawns, Spectracide Weed Stop for Lawns + Crabgrass Killer	Yes	Yes
quinclorac**	Drive XLR8	No	Yes
topramezone	Pylex	No	Yes

*These herbicides are primarily preemergence herbicides, but they have some postemergence activity on young crabgrass seedlings.

**Some herbicide products containing quinclorac also contain broadleaf weed killers, such as dicamba, 2,4-D, MCPA, and/or sulfentrazone.

Table 3B: Postemergence Herbicides to Control Emerged Crabgrass in Ornamental Beds and Landscapes.

Active Ingredient	Trade Names	General Public Use	Licensed Professional Use	Selective for Grasses	Labeled organic
ammoniated soaps of fatty acids	Pulverize, FinalSan	Yes	Yes	No	Yes
ammonium nonanoate	AXXE	Yes	Yes	No	Yes
caprylic + capric acids	Burnout Formula II, Dead Weed Brew,	Yes	No	No	Yes
caprylic + capric acids	Suppress, Fireworxx, Homeplate	No	Yes	No	Yes
d-limonene	Avenger	Yes	Yes	No	Yes
fluazifop	Ornamec, Fusilade II	No	Yes	Yes	No
fluazifop	Ortho Grass B Gon Garden Grass Killer	Yes	No	Yes	No
glufosinate ammonium	Finale, Cheetah Pro	No	Yes	No	No
glyphosate	Remuda Weed & Grass Killer	Yes	No	No	No
glyphosate	Ranger Pro, RoundUp Pro	No	Yes	No	No
pelargonic acid + fatty acids	Scythe	No	Yes	No	No
sethoxydim	Grass Getter	Yes	No	Yes	No

Herbicides for Ornamentals and Landscapes

In established ornamental beds, home gardeners have a very limited choice of preemergence herbicides to prevent crabgrass from emerging. These preemergence herbicides (oryzalin and trifluralin) can be applied either before crabgrass has germinated or after you’ve removed the weed by hoeing or hand pulling, but before another flush of germination.

A grass-selective postemergence herbicide containing fluazifop or sethoxydim can be used to control crabgrass growing around most broadleaved ornamentals. Nonselective postemergence herbicides such as glufosinate, glyphosate, and fatty acid soaps should only be carefully spot sprayed to avoid contact with desirable ornamental plants as severe injury to nontarget plants can occur.

Several herbicides labelled as organic or as organically-acceptable are available for use by home gardeners. The active ingredients are usually nonselective herbicides that can be spot sprayed on crabgrass. You may notice rapid weed damage on the first day after using these herbicides, but since contact herbicides do not translocate or move systemically within the weed, some weeds might slowly recover and regrow, requiring multiple successive applications.

Controlling crabgrass and other weeds in lawns and ornamental landscapes begins with knowing your local climate and growing conditions, selecting plants best suited to that area, and maintaining those plants to be as healthy and competitive against weed invasions as they can be. Cultural practices should be the main approach to avoiding crabgrass and other weeds, and herbicides are just one tool used to eliminate them.

References

DiTomaso JM, Healy EA. 2006. Weeds of California and Other Western States. UC ANR Publication 3488. Oakland, CA.

Flint ML, Reynolds CA. 2009. The UC Guide to Healthy Lawns. UC Statewide IPM Program.

Hart S. 2002. Crabgrass and Goosegrass Control in Cool Season Turfgrass. Rutgers NJAES Coop. Ext. Bul. E223.

LeStrange, M. and C. Reynolds. 2016. Pest Notes: Weed Management in Lawns. UC ANR Publication 74113. Oakland, CA.

Reicher Z., C. Bigelow, A. Patton, and T. Voigt. 2006. Control of Crabgrass in Home Lawns. (220 KB, PDF) Purdue Ext./Univ. of Ill. Publ. AY-10-W IL-IN TW 33.

Stapleton, J. J., C. A. Wilen, and R. H. Molinar. 2019. Pest Notes: Soil Solarization for Gardens and Landscapes. UC ANR Publication 74145. Oakland, CA.

UC Statewide IPM Program. 2016. UC IPM Pest Management Guideline: Turfgrass. UC ANR Publication 3365-T. Oakland, CA.

Based on an earlier version by Richard S. Molinar, UC Cooperative Extension, Fresno County (emeritus) and C.L. Elmore, Plant Sciences, UC Davis (emeritus).  

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