Page 106 - AG 7-2011 Revised 2016

Photo Courtesy of PBI/Gordon Corp. Large Crabgrass
(Digitaria sanguinalis)

Crabgrass is a summer annual that germinates when soil
temperatures reach a consistent 55 degrees F and is generally
killed at the first frost. Crabgrass leaves are rolled in the bud; the
first leaf appears short, wide and blunt-tipped. The ligule is tall and
membranous with jagged edges, and the auricles are absent.

The collar is broad with long hairs. Crabgrass is light green in
color, coarse bladed and will root at the nodes when they touch
the ground. A single crabgrass plant can produce up to 700 tillers.
It is a bunch type grass.

Immature Stage The inflorescence is a panicle of branches, with spikelets in two
rows. A crabgrass plant can produce 150,000 seeds. Crabgrass
needs warm soils and sunlight to germinate.

Crabgrass is found throughout the United States.

Integrated Pest Management Control Recommendations

Cultural Practices:
Do not seed, core aerate or verticut when soil and weather conditions are appropriate for the germination of
crabgrass. A slightly raised mowing height may help prevent the establishment of crabgrass by providing shade
from sunlight. When crabgrass is going to seed, lower the mowing height and collect clippings to prevent seed
establishment.

Herbicide Use:
Use a preemergent herbicide as soon as soil temperatures reach 55 degrees F for a period of four days.
A preemergent herbicide is recommended even if some crabgrass plants have germinated; there will still be
crabgrass seed in the soil which can prevent further infestation. Do not core aerate or verticut after a preemergent
herbicide application. For crabgrass control after germination, use a postemergent selective grass herbicide.

IDENTIFY YOUR WEEDS by Gary King, Ph.D.

One of the first things to do is to identify the problem weeds. You will need to know that weeds are usefully
grouped into 3 categories: Broadleaves, grasses, and sedges. The broadleaved weeds emerge from the seed
with their first 2 cotyledon leaves, which also gives them the name, dicot. Then they form more mature leaves
with characteristically branched or net-like veins. Broadleaves also have exposed growing point(s) at the top of
the plant and growing points in the leaf axils. They develop either a taproot or a thicker branched root system. As
the grasses and sedges emerge from seed, there is only at first a single cotyledon leaf, giving them the moniker,
monocot. These plants’ leaves have parallel veins that are easily seen on mature plants. Monocots have
protected growing points that send up shoots from below the soil surface. They also tend to have fibrous root
systems.

The number of cotyledon leaves gives you the first clue, and the subsequent growth further aids in identification
of the very youngest weeds (see page 102). With fresh samples of the seedling weeds and the flowers, fruit,
seed, and roots of the mature stages, your local agricultural advisor may use weed photos and plant keys to
determine the names of your weeds and help formulate your weed management plan.

Next, weeds are classified as annuals, biennials, or perennials. Annuals may either be winter/cool season
or summer/warm season types. They survive only one season, but must be stopped from producing seeds that
will germinate the next year. Biennials grow for 2 seasons, producing a rosette stage one year, followed the next
year by the dreaded seed production. Perennial weeds grow over many years, often producing many of those
nasty seeds over the years. Perennials are often the most persistent and difficult to control, since many also form
invasive or resistant structures such as stems that creep under the soil (rhizomes) or sneak over the soil surface
(stolons), as well as tubers or fleshy roots.

See Weed Growing Chart on page 106.

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