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first always understand your enemy;
to understand the crabgrass control that best fits your need.
Crabgrass is a common weed that almost everyone knows. There are two species of crabgrass common in USA:
smooth crabgrass, Digitaria ischaemum, and large or hairy crabgrass, D. sanguinalis. Both species
were introduced from Eurasia and are widespread throughout the United States. Crabgrass is found in turfgrasses
(mostly smooth crabgrass) and in ornamental landscapes (primarily large crabgrass). Large crabgrass is also found
in orchards, vineyards, and other agricultural areas. Crabgrass also has many other names including crowfoot grass
and summer grass
IDENTIFICATION AND LIFE CYCLE OF CRABGRASS AND THE BEST CRABGRASS CONTROL MEASURE TO TAKE
Smooth crabgrass is a low-growing, summer annual plant that spreads by seed and from rootings of the culm
nodes (joints) that lie on the soil. When unmowed it will grow upright to about 6 inches, but it will tolerate
mowing in turf at 1/4-inch and will still produce seed at this height. Seedling leaves are light green and
smooth. True leaves are dark green and smooth, and the leaf blade is from 1/4- to 1/3-inch across, up to 5-inches
long, and pointed. Crabgrass often forms patches in lawns, and plants can grow together to form large clumps. The
ligule (collar) is small and inconspicuous without prominent appendages or auricles. The leaf sheath and upper leaf
surface are smooth, but a few hairs may be found on the lower leaf surface. There may be a reddish tint at the base
of the leaf. The inflorescence (flower stalk) has 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.
When found in turf, large crabgrass is a low-growing summer annual that spreads by seed and from rootings
of nodes that lie on the soil. When unmowed it may grow upright to a height of 2 feet. It will not tolerate close
mowing as well as smooth crabgrass. Seedling leaves are light green and hairy. True leaves are generally 3
inches long and hairy on the upper surface of the leaf and leaf sheath. The collar region and flower stalk
are similar to that of smooth crabgrass, but the branches are longer, about 2 to 5 inches, at the end of the
The flowering stems of crabgrass are similar to those of bermudagrass (Cynodon dactylon), but the
spikelike branches on the flowering stems of bermudagrass originate at the same point whereas those on crabgrass
originate about 1/8- to 1/4-inch apart at the end of the stem.
In southern California, the major germination period for both crabgrass species is from January 15 to early
April, depending on the temperature, and seeds continue to germinate throughout spring and summer. While
germination is early in warm winter areas, growth is slow during spring months until mid-May. In June and July the
plants produce tillers and shoots, and flower in late July and August. In the absence of a frost, crabgrass may
overwinter in warm areas or during warm winters and produce new growth and a second crop of seed in spring or early
In the central and northern parts of the state, crabgrass begins germination around March 1 to 15 when soil
temperatures reach 50° to 55°F for at least 3 days. Germination continues throughout summer and into fall.
MANAGEMENT OF CRABGRASS
Cultural Control in Turfgrassspreads reproduces primarily by seed, any operation reduces seed
production will decrease crabgrass. There are also number operations that increase vigor turfgrass, thus decreasing
potential crabgrass invasion. These include proper mowing height turf, applying fertilizer at correct time year,
selecting best turf species for your area, overseeding keep the turfgrass thick, properly irrigating turf. to>
Mowing at the optimum height for turf increases turfgrass vigor and reduces the germination and
establishment of crabgrass. Select the proper mowing height from Table 1 for the dominant turfgrass species in your
turf. After mowing turf that is infested with crabgrass, thoroughly rinse mower to remove seeds, to avoid
transferring them to uninfested sites.
Table 1. Proper Mowing Height for Turfgrass Species.
||Mowing height (inches)
||0.5 or less
| Santa Ana
| tifway II
Fertilization can also be used to increase turfgrass vigor and reduce the possibility of a crabgrass
invasion. The best time to fertilize is when the turf is actively growing, which depends upon the turf species
grown (see Table 2). Because crabgrass is not very competitive, a vigorously growing turf will crowd out crabgrass
Table 2. Periods of Active Growth of Cool- and Warm-season Turf Species.
||Period of active growth
| annual ryegrass
||March-June and September-November
| fine fescue
||March-June and October-December
| Kentucky bluegrass
||end of February-end of May and October-December
| perennial ryegrass
||February-June and October-December
| tall fescue
||March-June and October-December
||April-end of September
| St. Augustinegrass
Selecting a turfgrass that is adapted to your local conditions will also help produce vigorous turf.
Cool-season species (bentgrass, bluegrass, perennial ryegrass, and tall fescue) are most competitive in coastal and
northern regions of California; some of the newer cultivars of perennial ryegrass, Kentucky bluegrass, and tall
fescue, however, are even more competitive and grow better than the older cultivars. For example, tall fescue
cultivars used for turf vary in their competitive ability with both smooth and large crabgrass. The older fescue
varieties (Fawn and Kentucky 31), which grow in an open, upright manner, tend to become invaded by crabgrass. The
slower-growing, dwarf-type tall fescue varieties (especially Bonsai) are also easily invaded. Warm-season species
(bermudagrass, St. Augustinegrass, zoysiagrass, and dichondra) are most competitive with weeds in interior valleys
and desert regions; kikuyugrass is more competitive in south coastal regions.
Irrigation timing and amount can also affect crabgrass germination and growth. Turf that is overwatered
or has frequent (daily) light irrigations becomes weak and vulnerable to invasion by this weed. Irrigating
infrequently (once a week) will improve turf vigor. Crabgrass is often found first in open areas where there is no
turf, along sidewalks where the soil may be warmer, or around sprinkler heads where turf is mowed closer.
Cultural Control in the Landscape
SURFLAN IS BEST IN YOUR SHRUB BEDS AND FLOWER BEDS
In shrub beds, bedding plants, or around trees, mulching with wood products (wood chips, nuggets), composted
yard waste, or synthetic landscape fabrics covered with a mulch will control the germination and establishment of
crabgrass by blocking sunlight needed for its germination and growth. The depth of a mulch depends on the size of
the particles: coarse mulch may need to be 3 to 6 inches deep to control all weeds, whereas a finer mulch may need
to be only 2 to 3 inches deep.
Mulch that has been on the soil for a while can provide an adequate growth medium for weeds to germinate and
grow in. If seedlings are germinating in the mulch, move the mulch about with a rake to reduce their establishment.
Hand-pull escaped crabgrass plants before they seed. Flaming with a hand-held burner will control crabgrass
seedlings, but be careful not to set fire to the mulch if it is composed of wood chips or compost.
Clear plastic mulching (solarization) is effective for eradicating crabgrass plants and seed if it is applied
during periods of high solar radiation. In California's Central Valley, this means during June to August, whereas
in coastal areas the best time may be August to September or May to June when fog or wind is most likely to be at a
minimum. Before applying the plastic, closely mow the crabgrass, remove the clippings, and water the area well. It
is not necessary to cultivate before solarization, but a shallow cultivation may improve control. Place clear,
ultraviolet (UV)-protected polyethylene over the area for 4 to 6 weeks. Shade will reduce the effectiveness of
solarization because it limits the amount of radiation. Solarization works most effectively when there is no slope
in the land or if there is, the slope has a south or southwest exposure. Temperatures are not as high under plastic
placed on a north-facing slope; consequently, control is not as effective. After solarization, do not cultivate the
area deeper than 3 inches to avoid bringing weed seed into the upper soil layer. (See the soil
Chemical ControlCrabgrass is easy to control in both turfgrass and ornamental beds with herbicides
that are applied before it germinates (preemergent herbicides) or after it germinates (postemergent herbicides).
Read the label to make sure the product can be used on your turf type and around the ornamentals in your landscape.
Turfgrass. Preemergent herbicides that are available for the home gardener for crabgrass control in
warm-season (bermudagrass, zoysiagrass) and cool-season grasses (perennial ryegrass, Kentucky bluegrass, tall
fescue, fine fescue) include pendimethalin, bensulide, benefin, and trifluralin. (Professional pesticide
applicators may also use dithiopyr, oxadiazon, and prodiamine.) Oryzalin is also available to the home gardener,
but it is for use in warm-season turf only. Preemergent herbicides must be applied before the crabgrass germinates
(usually from mid-January in southern areas of the state to early March in cooler areas).
Use postemergent herbicides when the crabgrass is small (i.e., in the 1- to 3-leaf stage). If the crabgrass is
larger, it takes more herbicide to control it and there is a greater chance of injury to the turfgrass. The
postemergent herbicide (MSMA) is effective on young crabgrass. When in the 1- to 3-leaf stage, crabgrass can be
controlled with one application. If it is larger, more than one application will be required. If temperatures are
over 85°F, reduce the rate of the herbicide or the turf may be injured. If temperatures are higher than 95°F, do
not make an herbicide application. Dithiopyr can also be used for postemergent control if the crabgrass is young
and has less than five leaves.
Ornamental Beds. In landscape areas, crabgrass can be controlled chemically in the home garden with the
selective preemergent herbicides oryzalin, trifluralin, and benefin. (Landscape professionals may also use
oxadiazon, pendimethalin, and prodiamine.) These materials can be used before crabgrass germinates or after the
crabgrass is removed by hoeing or hand-pulling and before crabgrass germinates again.
Crabgrass can be controlled with a postemergent selective herbicide (sethoxydim plus oil, fluazifop, or
clethodim) that can be used over or around most broadleaved ornamentals, or with nonselective herbicides such as
glyphosate, pelargonic acid, or glufosinate-ammonium. All of these herbicides except clethodim are available for
use by the home gardener. Use nonselective herbicides with care to prevent them from contacting desirable shrubs.
Control crabgrass before it sets seed; seeds of crabgrass can remain viable at least 3 years in soil.
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