Annual grasses are species which germinate from seed, complete their life cycle, produce seeds, and die within a year. Annual grasses are not the only undesirable grass weeds to infest lawns--there are many perennial grass species which are equally pervasive and pernicious. Perennial grass weeds such as quackgrass, nimblewill, brome-grass and others are often confused with annual grass weeds.

Crabgrass is the most common and troublesome weed among annual grass weeds in lawns. Large or hairy crabgrass and small or smooth crabgrass are both quite com-mon in lawns. Others include foxtails, barnyardgrass, goosegrass and annual bluegrass.

Control Methods:

Cultural Control: An integrated weed management program is a combination of recommended cultural practices and the use of herbicides when necessary. Producing a dense, healthy stand of turfgrass is the best way to control annual grass weeds and other broadleaf weeds. The proper mowing height and frequency, fertilization and irrigation are part of any weed control program and should be practiced throughout the growing season.

Chemical Control: Selective annual grass weed control can be obtained with herbicides. Preemergence herbicides provide effective control of crabgrass and other annual grass weeds for several weeks or months, depending upon dosage and products. The effectiveness of these materials is based upon their ability to provide excellent weed control with no turf injury.

Timing is important for herbicide application. It is necessary to apply preemergence herbicides before annual grass seeds germinate. The application will not be as effective if you apply these herbicides after annual grasses emerge above-ground.

The preemergence herbicides should be applied two weeks prior to the expected weed seed germination period. The best time for annual grass weed control is late April in Rhode Island. The herbicides should be watered-in so that the chemical can form a barrier in the soil prior to weed seed germination. The resulting chemical barrier should not be disturbed during weed germination periods.

See table for list of commonly used preemergence products. Selective control of germinating annual broadleaf weeds such as chickweed, yellow woodsorrel and prostrate spurge can be obtained with these preemergence treatments. All of these herbicides can be used on established turfgrass. Siduron is the only preemergence herbicide that can be used for seedling turf or at time of seeding. However, Benefin and DCPA can be applied in the spring following a fall seeding.

Trade name, common name, formulation and rate of commonly used preemergence products

Adapted from the University of Massachusetts Extension, 1999