of Rhode Island GreenShare Factsheets
crabgrass, also known as hairy crabgrass, finger grass, crow foot,
purple crab-grass and Polish millet, is native to Europe or Eurasia
and is distributed worldwide. It was introduced into the U.S. in
1849 by the U.S. Patent Office as a potential forage crop. It is
now found in almost every crop or non-crop situation. There are
two closely related species of crabgrass in the United States--large
crabgrass (Digitaria sanguinalis) and small, or smooth, crabgrass
Large crabgrass, a summer annual, is a member of the grass family.
It is one of the most troublesome weeds in lawns. Crabgrass reproduces
by seeds. It has a prolific tillering or branching habit. A single
plant is capable of producing 150 to 700 tillers and 150,000 seeds.
Crabgrass plants are very adaptive to mowing height. Plants can
produce seeds at mowing heights as low as 1/2-inch. Crabgrass germination
is related to soil temperature. When the soil temperature reaches
60 degrees F, crabgrass begins to germinate. However, the soil temperature
must be in this range at least for a week. Seeds germinate best
from early spring to late summer. Crabgrass seeds are dormant for
a short period of time after they shed from plants. Crabgrass continues
to grow until midsummer when days become shorter, and vegetative
growth slows as plants enter their reproductive stage. Purplish
seed heads form until frost kills the plants. Plants that emerge
early in the season and have a long period of vegetative growth
are much larger and more competitive than plants that germinate
late in the season.
is found in almost every situation. It is prolific in lawns, golf
courses, athletic fields, gardens, orchards and waste places, and
thrives well in lawn situations. Once established, it tolerates
both high temperatures and dry weather conditions.
is very noticeable in lawns. It is a rapid growing, coarse textured
yellowish-green grass that is conspicuous when found growing among
fine textured, dark green cool-season turfgrasses. The stems spread
outward and are very branched. Roots develop at nodes on the prostrate
stems. The first leaf is only about twice as long as it is wide.
It is tinged light purple and has a white strip ninning down the
center. Both sides have silky, shiny hair. Leaves are 2/5- to 1/2-inch
wide and 1/3- to 1-inch long. The leaf sheaths of large crabgrass
seedlings are tinged purple and are covered with long stiff hairs.
The ligule, a thin membrane or row of hairs at the top of the junction
of the leaf sheath and the leaf blade, is membranous, flat at the
top and smooth. Large and small crahgrass are the only species of
the grass family which have a membranous ligule. Auricles, the appendages
projecting around the stem from both sides of the collar, are absent.
basic principle of a crabgrass control program is to prevent reinfestation
by seeds. Controlling seed production for several years will help
reduce the viable seed supply. Crabgrass cannot be controlled in
one growing season because of the great number of viable seeds that
accumulate in the soil from years of infestation. A good weed management
program in lawns is one that consists of both recommended cultural
practices and the use of herbicides as appropriate for the control
of any given species. Satisfactory control may require several seasons
of conscientious adherence to a good control program.
Establishing a dense and healthy stand of turfgrass is the best
way to control crabgrass and other annual weeds, including grasses
and broad-leaf weeds. The proper mowing height and frequency, fertilization
and irrigation are part of the weed control program and should be
practiced throughout the growing season.
Seed in late summer for new lawns. Crabgrass and other annual
grasses that germinate in late summer will be killed by frosts
in October or November.
Mow your lawn to a height of 2 to 3 inches. The taller grass shades
the soil and keeps soil cool. Crabgrass seeds do not germinate
under cool conditions. Adjust your cutting height as appropriate
for the turfgrass species.
Water heavily once a week and avoid frequent light irrigation.
Avoid summer fertilization. Crabgrass benefits more from fertilizer
application under high temperatures than Kentucky bluegrass and
other cool season grasses.
Crabgrass can be selectively controlled in turfgrass areas by judicious
use of preemergence or postemergence herbicides. Timing is important
for herbicide application. The best time for preemergence application
of herbicides is late April or early May. Postemergence herbicides
can be used when crabgrass is in the 2- to 5-leaf stage. Repeat
applications may be required depending upon the treatments.
caution when seeding a new lawn in the spring. Only use a crabgrass
preemergent control containing siduron as it will not kill desirable
grass seeds (other crabgrass preemergent controls will).
from the UMASS Extension, 2001
are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
be stored with foods or in areas where people eat.
When trade names are used for identification, no product endorsement
is implied, nor is discrimination intended against similar materials.
Be sure that the pesticide you intend to use is registered for
the state of use.
The user of this information assumes all risk for personal injury
or property damage.
information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
of Rhode Island Cooperative Extension provides equal program