STEPS TO A SUCCESFUL LAWN

Preventing and Controlling Crab grass

What Is Crabgrass? Crabgrass is the primary weed pest of the Mid-Atlantic region. its spreading, aggressive growth habit crowds out desirable grass species in your lawn.

Crabgrass is a warm season annual grass. While it germinates in spring, its most vigorous growth depends on warm summer days. Crabgrass seed germinates when soil temperatures reach 65° for at least one week. This usually occurs in the Washington area at the end of March or during the first few weeks of April. The small plants blend in with the surrounding grasses until hot weather arrives in June or July. In response to the high temperatures, our cool weather desirable grasses (Bluegrass, Fescues, Ryes) slow their growth until the cooler weather of the fall. Unfortunately, crabgrass accelerates its growth and can soon dominate the lawn.

Growth of crabgrass will slow or stop with cooler weather in the fall, but by then it may have already crowded out the desirable plants. Since crabgrass is an annual weed, it will die with the first hard frost, leaving unsightly patches in the turf and enormous quantities of seed behind. Spring begins the cycle all over again.

How to Prevent Crabgrass

The best way to rid lawns of crabgrass is to prevent its germination from seed. A preventive application of a preemergent crabicide shortly before the seed germinates will go far toward ridding lawns of this pest. Crabgrass seeds begin germinating in the Washington area approximately the first week of April (weather depending) and continue to germinate until the beginning of July. The largest flush of seed will germinate in April, so this is the key time for control. After crabgrass seed has germinated, preemergents will have little effect on the growing weed.

Preemergent Application

Typically, preemergents must be applied at the end of March, before the crabgrass seed germinates. Preemergents must be lightly watered in immediately after application. A delay of even an hour will reduce the effectiveness of the product. Also, the soil should not be disturbed after the crabicide is applied because it will disrupt the coverage in that area. Preemergent crabicides have differing residua effects. Some will last the entire season; most will last 9 to 12 weeks, thus requiring a second, lighter application in mid-June. Preemergents will also adversely affect grass seed, so lawn seeding cannot be undertaken once a preemergent is applied unless the preemergent is Tupersan.

Tupersan permits turf seeding to occur upon application, but it has a very limited residual effect on crabgrass, only 4 weeks. If you wish to seed your lawn and prevent crabgrass at the same time, you must seed, apply Tupersan, then apply a stronger, longer lasting preemergent 4 weeks later for season-long control. If a long-lasting preemergent has been applied and subsequently the lawn has to be seeded, you must cultivate extensively and apply activated charcoal to neutralize the preemergent.

Post-Emergent Crabicides

Once crabgrass germinates, preemergents will generally not be effective. You may not notice a problem until hot weather in July accelerates the pest’s growth, and suddenly, seemingly overnight, the lawn is inundated with this weed. Post-emergents are available, but they usually must be applied several times over a 10-day period, and they present a risk of burning the desirable turf unless sufficiently watered in. Post-emergents are best used by the first weeks of July or when the crabgrass has not passed the four leaf-two tiller stage. The lawn should not be mowed immediately before application of a post- emergent, and good soil moisture is a must. Also, broadleaf herbicides should not be applied within 2 weeks of the use of post-emergents.

Preventive Steps

Prevention of crabgrass invasions is best accomplished by having a thick, vigorous lawn. Proper fertilizing schedules and amounts (see Johnson’s Fertilizing Your Lawn) along with the appropriate mowing height will keep crabgrass seed from getting a foothold in your lawn.

  

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