Invasion of the Turf Snatchers
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06/04/2007 12:35 PM
Friday, April 6, 2007
Invasion of the Turf Snatchers!
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 unles