Has your lawn been invaded by crabgrass? Without a doubt, this common, annual grass can be one of the most frustrating turf weeds in the Washington, D.C. area. The seeds germinate in spring and grow rapidly as the temperatures rise. Crabgrass is extremely drought tolerant, prefers full sun, and is typically found in disturbed soils or where turf has a tough time becoming established. Two species of crabgrass are widespread in the mid-Atlantic region: Large, or hairy, crabgrass, Digitaria sanguinalis and smooth crabgrass, Digitaria ischaemum. A third species, southern crabgrass (Digitaria ciliaris), is a problem in the southeastern United States.

At the U.S. National Arboretum we manage our pests—plant, insect, and disease—with a program called Integrated Pest Management (IPM). IPM means using a combination of methods to control and prevent pests. While there are several good pre-emergent herbicides that are effective in controlling crabgrass, the best method is to exercise good cultural care; encouraging strong turfgrass development will keep crabgrass, as well as other weeds, at bay.

Before taking any drastic measures against the dreaded crabgrass in your lawn, a soil test is highly recommended. This simple test will help pinpoint any underlying problems that may be hindering strong turf development (e.g. soil pH, soil type). Mowing turf high —2.5 to 3.5 inches, depending on turf type—and mowing regularly with sharp blades are equally important. Dull blades often shred or bruise the desirable grass leaving it weakened and more vulnerable to invading weeds. Crabgrass tends to become a problem in thin stands of turf. If the density in your lawn is low, core aeration and overseeding will give your lawn a boost. Aeration and seeding is best done in the fall, with spring being the next best time. Irrigation of turf may also be necessary unless precipitation is adequate (an inch per week is a good rule of thumb).

If an herbicide is desired, there are several available to the homeowner. Products with the active ingredients dithiopyr (Dimension) or pendamethalin (Pre-M) are good options. When opting for an herbicide treatment, make sure you have it applied by late March. This will allow enough time for spring rains to disperse the chemical. An important point to remember when considering herbicide use is no chemical can solve a problem created by poor growing conditions. Crabgrass will continue its assault on your lawn until you incorporate the beneficial practices mentioned above.

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