Preventing and Controlling Crabgrass
May 11, 2008
Crabgrass (Digitaria spp) is one of the most common weeds in American lawns. It is a warm-season annual weed which means it reproduces by seed and is killed off in the fall by frost. Crabgrass is not shade tolerant, and grows best in full, hot sun.
Crabgrasses can be controlled with pre-emergent herbicides that interfere with a key enzyme when a seed germinates. As their name suggests, preemergent herbicides kill crabgrass at a specific time: before its seedlings emerge. If they are applied to the soil too early, they get washed too deep into the soil by rainwater. If they are applied too late the key enzyme inhibited is no longer active.
So how do you know the proper time? In the Northeast and Northwest, crabgrass germination coincides approximately with the blooming of lilac bushes and forsythia bushes. In the South, preemergent herbicides application should coincide with the bloom time for dogwoods, redbuds and azaleas. In the Southwest, crabgrass can start germinating as early as mid-January if the winters have been warm. If you’re still not sure, a good rule of thumb is crabgrass will germinates when soil temperatures reach 50° to 55°F for at least 3 days.
Usually one application put down at the proper time gives control. If an application is made very early in the season, a second application may be necessary during mid- to late June to kill later germinating crabgrass. Always follow pre-emergent herbicide applications with one-quarter to one-half inch of water. This helps move the herbicide to the soil surface where it provides the control. Also, watering in the herbicide may reduce your exposure to the product.
What should you do if you miss the window of opportinuty of applying pre-emergent herbicides? Old fashioned weeding is probably the best method of crabgrass control once it has germinated. Hand-pulling small patches of crabgrass before it goes to seed is the quickest and easiest way to control it. To facilitate weeding, water the lawn first (weeds are more easily extricated from wet soil). Then remember to apply a pre-emergent herbicide next Spring.
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[...] Crabgrass (Digitaria spp) is one of the most common weeds in American lawns. It is a warm-season annual weed which means it reproduces by seed and is killed off in the fall by frost. Crabgrass is not shade tolerant, and grows best in full, hot sun. Crabgrasses can be controlled with pre-emergent herbicides that interfere with a key enzyme when a seed germinates. As their name suggests, preemergent herbicides kill crabgrass at a specific time: before its seedlings emerge. If they are applie Lawn Care Tips… [...]