How To Kill Crabgrass In A Lawn

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This article provides tips for how to prevent or kill crabgrass in lawn grasses
by Brett · All Zones · Lawn Care · 2 Comments · April 23, 2013 · 7,562 views

What Is Crabgrass?

Crabgrass is a type of annual grass (lives for less than a year) that appears in lawns and landscape beds during the warm season. Depending on weather and soil temperatures, crabgrass seeds begin to germinate mid- to late- spring in the lawn and, after doing so, it isn't long before the clumps of foliage are visible.

If it weren't an annual, perhaps crabgrass might be a suitable grass for lawns...it sure is stubborn and hard to kill, and reliably reseeds itself! However, unlike other perennial warm-season grasses such as Bermnuda, Centipede and Zoysia, which keep their dormant foliage intact during winter, crabgrass dies back completely during the cool season. Therefore it would leave nothing but unsightly dead foliage and, more likely, bare dirt during the winter.

The term "crabgrass" can actually refer to several grasses. The two most common species that invade lawns are Hairy Crabgrass (Digitaria sanguinalis) and Smooth Crabgrass (Digitaria ischaemum). Depending on climate and maintenance practices, these can either grow with high branching stems or they can form low, spreading mats of foliage. When lawns are mowed regularly they usually form mats. These mats will spread and put out roots within a season.

If allowed to flourish, crabgrass tends to choke out the lawn grass surrounding it, forming depressions in a lawn. Then, as already mentioned, will reseed each spring allowing it to spread even further the next season.

How to control or kill crabgrass?

In the past, before the arrival of preventer products, when crabgrass had colonized in a lawn it was very difficult to eradicate. It overwhelmed desirable lawn grasses with an aggressive seeding pattern and rapid growth habit. As a result, as it emerged, most gardeners spent hours digging up each clump by hand. Then along came the crabgrass preventer products, which killed crabgrass seeds before or when they started to germinate.

To this day, the use of lawn weed preventer is still the best long term method for control of crabgrass. But this article isn't about prevention...it's about killing crabgrass after it has already sprouted in the lawn.

If you're not on a lawn weed prevention program chances are you battle with crabgrass every year, or have given up on the battle altogether and just let it take over the lawn every summer? Even if you're on a prevention program, or have just started, there's still the possibility you'll see some clumps of crabgrass pop up randomly in the lawn. Either way, there are now herbicide sprays available you can use to kill crabgrass after it has sprouted. The type of herbicide you use will depend on the type of lawn grass you are growing.

Warm Season Lawn Grasses (Bermuda, Centipede, St. Augustine, Zoysia)

Cultural Control - A number of steps can be taken to eliminate crabgrass in warm season lawns, such as Bermuda, Centipede, St. Augustine and Zoysia. The first is to grow and maintain a healthy, dense turf that does not allow this grassy weed to take root and compete. If your lawn grass is unhealthy, it's a good idea to first test the soil to make sure the pH is right, and to find possible nutrient deficiencies.

Bermuda and Zoysia grasses thrive in a neutral to slightly alkaline soil pH between 6.5 to 7.0 on the pH scale. Centipede and St. Augustine thrive in a more acid soil with a pH between 5 to 6. To make soil more acid apply lime sulfur, chelated iron or aluminum sulfate. To make soil more alkaline apply pelletized lime.

Keep the lawn well fed. Apply fertilizer in spring, early summer, and again in early fall with a "fall feed." Avoid the use of quick-releasing high-nitrogen fertilizers.

Warm season grasses are more heat and drought tolerant than cool season grasses. However, during prolonged periods of dry weather provide supplemental water to keep the lawn healthy and free of stress. It's best to water more deeply and less frequently. Never remove more than 1/3 the height of the grass in a single mowing. Cut often enough to avoid clumping during mowing.

When all else fails to eradicate crabgrass from your warm season lawn, there are now chemical herbicides that can be useful to kill it. Below are recommendations for the various types of warm season grasses.

Chemical Control in a Bermuda or Zoysia Lawn - The best product I've found to kill crabgrass plants in a Bermuda and Zoysia lawn is Fertilome Weed Out with Q. In addition to killing crabgrass, Weed Out with Q kills over 200 other grassy and broadleaf weeds, roots and all.

Chemical Control in a Centipede or St. Augustine Lawn - There are three products I've found that work well to kill crabgrass plants in Centipede or St. Augustine lawns: Fertilome Over The Top II, Hi-Yield Grass Killer and Vantage. All of these products are liquid concentrates which contain a chemical called Sethoxydim.

*NOTE: When using chemicals always follow the instructions for mixing and application on the product label. Unless weeds are widespread spot treatment is recommended.

Cool Season Lawn Grasses (Fescue, Bluegrass)

Cultural Control - As with the warm season lawn grasses, there are a number of steps that can be taken to eliminate crabgrass in cool season lawns, such as fescue or bluegrass.

The first is to grow and maintain a healthy lawn that does not allow this grassy weed to take root. If you have a fescue or bluegrass lawn, plan on overseeding and fertilizing in early fall. Then fertilize again in spring, before crabgrass emerges, so that the lawn can get a head start.

Have your soil tested to make sure the pH is in the range for fescue and bluegrass to thrive (6.5 to 7 ph). Apply pelletized lime if the soil is too acidic.

In the absence of rainfall, keep the lawn watered sufficiently: deeply and infrequently is best.

To help shade out the crabgrass seeds, and keep them from germinating, keep the turf relatively high when you mow - cutting it no lower than 3 inches in height. Never remove more than 1/3 the height of the grass in a single mowing. Cut often enough to avoid clumping during mowing.

Chemical Control - When all else fails to eradicate crabgrass from your fescue or bluegrass lawn, there are chemical herbicides that can be used to kill the plants. The best product I've found is Fertilome Weed Out with Q. In addition to killing crabgrass, Weed Out with Q kills kills over 200 other grassy and broadleaf weeds, roots and all.

*NOTE: When using chemicals always follow the instructions for mixing and application on the product label.

Hope this information was helpful to you!


Gardenality.com

Gardenality.com · Gardenality Genius · Zone 8A · 10° to 15° F
Hi Jerome - Glad you found it helpful! If you ever have any gardening related questions don't hesitate to ask them in Ask Experts. You'll see the tab for Ask Experts in the main navigational bar at the top of every page in Gardenality.

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