Cooperative Extension Service
The University of Georgia College of Agricultural and Environmental Sciences
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Control Crabgrass (Digitaria spp.) In Ornamentals

Mark Czarnota, Ph.D., Ornamental Weed Control Specialist
University of Georgia, College of Agricultural and Environmental Sciences
Department of Horticulture, 1109 Experiment Street
Griffin, GA 30223

What Makes This Plant a Weed
How Do I Get Rid of Crabgrass?
Table 1: Preemergent herbicides used to control crabgrass from seed in ornamental situations
Table 2: Postemergent herbicides used to control crabgrass in ornamental plantings

From late spring until frost, it is hard not to notice the myriad of annual grasses that invade our landscapes. A large portion of these annual grasses are crabgrass. The genus Digitaria is composed of approximately six species. Three of these species are generally the "problem weeds," and they include Large crabgrass (Digitaria sanguinalis), Southern crabgrass (Digitaria ciliaris), and Smooth or Small crabgrass (Digitaria ischaemum). All crabgrasses have similar growth habits and flowering structures, but species are separated by minor differences in the flower structures and leaf pubescence. Refer toColor Atlas of Turfgrass Weeds, by L.B. McCarty, John W. Everest, David Hall, Tim Murphy and Fred Yelverton; and Weeds of the Northeast, by Richard H. Uva, Joseph C. Neal and Joseph M. DiTomaso for excellent descriptions on how to identify species.

What Makes this Plant a Weed?

Several undesirable characteristics make crab-grasses unwanted in the landscape. First, all crabgrasses are annual weeds, and a single plant is capable of producing 150,000 seeds in one season. In turfgrass, plants that invade during the spring and summer (Figure 1) will leave large voids in the fall and winter. Second, crabgrass has an ungainly texture that doesn't fit into the landscape scheme (Figure 2). In the vegetable garden, crabgrass quickly out-competes desirable vegetables, causing considerable yield reductions.

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Figure 1. Crabgrass (A) growing in a bermudagrass turf (B).		Figure 2. Crabgrass making itself at home in a clump of Black-eyed Susans.

Crabgrass seed has a long germination period; if conditions are right, it can germinate throughout the growing season. Despite its weediness, crabgrass does have a few redeeming qualities. Apparently the seeds can be toasted and ground for flour, used to make porridge or fermented to make beer. It also has decent nutrient qualities as a forage.

How Do I Get Rid of Crabgrass?

Crabgrass traditionally has been controlled with preemergent herbicides (Table 1) applied early in the spring, which prevent crabgrass seeds from germinating. Recently several postemergent selective herbicides (Table 2) have been shown to effectively control crabgrass after it germinates. This has vastly increased our ability to control crabgrass. Now we can control crabgrass when we see it, and preemergent herbicides are not essential. These postemergent grass herbicides kill or severely injure many species of actively growing grasses. Be careful to avoid spraying ornamentals or desirable turf grasses. With many businesses, however, any crabgrass germination is unacceptable and preemergent herbicides are still the mainstay of control.

If you try to control crabgrass after it has germinated, preemergent herbicides will generally not work. The only exception is Dimension (dithiopyr) a preemergent which also controls crabgrass that has not produced more then three tillers (lateral shoot). As with all pesticides, read the label to be certain that the desirable plant(s) that will come in contact with the herbicide are tolerant of that particular herbicide.

In established ornamental plantings, mulches and landscape fabrics also provide excellent crabgrass con-trol.

Attention!

Pesticide Precautions

• •It is the responsibility of the pesticide user to observe all directions, restrictions and precautions on pesticide labels. It is dangerous, wasteful and illegal to do otherwise.
• •Store all pesticides in original containers with labels intact and behind locked doors. Keep Pesticides out of the Reach of Children.
• •Use pesticides at correct label dosage and intervals to avoid illegal residues or injury to plants and animals.
• •Use pesticides carefully to avoid drift or contamination of non-target areas.
• •Surplus pesticides and containers should be disposed of in accordance with label instructions so contamination of water and other hazards will not result.
• •Follow directions on the pesticide label regarding restrictions as required by State or Federal Laws and Regulations.
• •Avoid any action that may threaten an endangered species or its habitat. Your county extension agent can inform you of endangered species in your area, help you identify them and, through the Fish and Wildlife Service Field Office, identify actions that may threaten endangered species or that habitat.

Trade and brand names are used only for information. The Cooperative Extension Service, University of Georgia College of Agricultural and Environmental Sciences does not guarantee nor warrant published standards on any product mentioned; neither does the use of a trade or brand name imply approval of any product to the exclusion of others which may also be suitable.

Circular 867-7/May 2004

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