Crabgrass

crabgrass, Joseph Berger, Bugwood

Crabgrass photo, courtesy of Joseph Berger, Bugwood.org

This time of the year is always full of activities to do outside. It is a great time to get outside in the comfortable weather. Lawncare is always at the top of our spring outdoor ‘to do’ list, and crabgrass is number one on the concerns.

Crabgrass Basics

Crabgrass is a summer annual grassy weed that takes advantage of thin areas in our lawns to become established. As a summer annual weed, crabgrass germinates in the spring and, if not controlled, new plants continue to germinate throughout the summer. Each plant grows for one summer, then dies with the first hard frost in the fall. New crabgrass that you see in your lawn each year is from seed that was set the previous year by the crabgrass growing before.

Crabgrass is a problem in our lawns. Each plant will compete with our desirable grass species. Once crabgrass gets into a lawn, it will compete with our grass for water, sunlight and growing space. Plants produce a large amount of seed that will germinate the following year, creating an ongoing problem on your lawn.

Prevention

Crabgrass is difficult to eradicate once it becomes established, so it is better to prevent this weed from becoming established in the first place. Crabgrass preemergent herbicides are used to inhibit the growth of young seedlings, destroying them before they can emerge from the soil. Which is why many people prefer to use a preemergent herbicide to control the crabgrass in their lawn.

Preemergent herbicides should be applied before crabgrass has started to germinate, which happens when soil temperature has reached 55-60 degrees F, measured at 4-inch soil depth, for at least four days. This is not based on a date range, because soil temperatures differ from year to year. It is based on the weather conditions for that year. We have reached that point now this year.

It is not beneficial to apply the preemergent too early in the year. Once applied products begin to degrade and breakdown. If your application is made too early, before crabgrass germination has started, you are wasting your product and monty because you will have a shortened period of control once crabgrass does start germination.

Plan on making two applications of preemergent to give season-long crabgrass control. Purchase enough product in spring for two applications; garden centers often run out of preemergent products by the end of spring so it could be hard to find later in summer. Each product has a slightly different length of residual action, so follow the product’s label directions on when the second application should be made.

Controlling Existing Plants

Post-emergent herbicides can be used to control crabgrass that has emerged in your lawn. Products containing Mesotrione, commonly found in the product called Tenacity, works as both a pre- and post- emergent herbicide on grasses and broadleaf weeds. It can also be used at seeding if you have a history of crabgrass problems and need to overseed.

The other commonly used post-emergent herbicide for controlling crabgrass would be products that contain Quinclorac, commonly found in the product called Drive.

If crabgrass does appear in your lawn, you can reduce future problems by keeping plants mowed short enough that they don’t produce seedheads. Then at least there won’t be additional seed in the soil to increase your problem next year.

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