Home & Garden Tips
Controlling Crabgrass in the Garden
By Roosevelt McWilliams County Extension Agent

At this time of year it is hard not to notice the myriad of annual grasses that have invaded our garden. A large portion of the annual grass is crabgrass. The genus Digitaria constitute all crabgrass. This genus is composed of approximately six species. Three of these species are generally the problem weeds, and they include large crabgrass, southern crabgrass, and smooth or small crabgrass.

All crabgrass has similar growth habits and lowering structures, but species are separated by the minor differences in the flower structures and leaf pubescence.

There are several undesirable characteristics that make crabgrass unwanted in the garden. First, all crabgrass are annuals. This is very undesirable in turf grass. In the fall and winter, large voids are left where crabgrass had invaded. In the flower garden, crabgrass ungainly texture doesn't fit into the desirable vegetables causing considerable yield reductions. Crabgrass seeds have a very long germination period, and basically germinate for the entire growing season if the growing conditions are right. A single plant can produce 150,000 seeds in one season.

For about 20 years, crabgrass has traditionally been controlled by prevention. Pre emergent herbicides (pendimethalin, trifluralin, and oryzalin) applied early in the spring, prevent crabgrass seeds from germinating. About 10 years ago, several post emergent selective herbicides (dithiopyr, clethodim, sethoxydim, fenoxyaprop, and fluazifop) were found that controlled crabgrass after it germinated. This has vastly increased our ability to control crabgrass.

With many businesses, however, any crabgrass germination is unacceptable and pre emergent herbicides are still the mainstay of control. In turf grass, dithopy (Dimension), pendimethalin (Scotts products containing Halts), prodiamine (Barricade), and oryzalin (Surflan) do an excellent job of preventing crabgrass germination.

In the landscape, trifluralin (Preen) and pendimethalin (pendulum or Corral) are a few pre emergent herbicides that are available for crabgrass control. If you are trying to control crabgrass after it has germinated, pre emergent herbicide will not work.

There are several post emergent herbicide that are available for controlling crabgrass in the landscape. Depending on the turf grass or ornamentals that are being treated will determine which one to use.As with all pesticides, make sure to read the label to be certain that the desirable plants that will come in contact with the herbicide are tolerant of that particular herbicide. In established ornamental plants, mulches alone and in combination with landscape fabrics can also provide an excellent crabgrass control as well controlling many other annual weeds.