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Schmidt: Controlling crabgrass

September 23, 2016
Yolanda Schmidt - County Agent , Pierce County Tribune

In an NDSU Extension office, it often takes only a couple of seasons before an agent is soon able to start predicting the types of calls that will begin coming into the office with the changing of the seasons. So, it doesn't surprise me that a number of homeowners from around the county have been calling or bringing in samples for identification and to inquire about how to control this grass that is suddenly "taking over their lawn". Which is why I decided to write about this troublesome grass in this week's column.

This troublesome grass is called crabgrass, Digitaria spp. Because of its flat vs. upright growth habit most home owners don't really notice it until the seed heads start to change color in late summer/early fall.

Crabgrass is easily controlled with a combination of pre-emergence herbicide and basic cultural practices. However, depending on current infestation level and existing seed bank, complete control may take several seasons.

Common North Dakota lawn grasses, Kentucky bluegrass and red fescue, are perennial cool season grasses. Crabgrass is a warm season annual grass which grows best in the heat of mid-summer when desirable lawn grasses are often semi-dormant and offer little or no competition. Crabgrass overwinters as seed, comes up about mid-May (about the time forsythia begin to bloom or roughly about 2 weeks before lilacs bloom) and later, and is killed by fall frosts. Crabgrass is not shade tolerant and grows best in full sun.

Simply mowing crabgrass won't stop it since it grows more flat than upright and keeps producing seeds, week after week, until you kill it or cold weather arrives. Each plant has the potential to produce 10,000 or more seeds.

Once this troublesome weed has gotten started in your yard, there are several things you can do to get control over it. The step or stage that is best for starting will depend on the season in which you begin.

Steps for Controlling Crab Grass

1. Keep crabgrass seeds from spreading.

2. Kill existing crabgrass.

3. Remove dead crabgrass plants.

4. Replant bare lawn spots with new grass seed.

5. Apply a crabgrass preventer at the appropriate times.

6. Set your lawnmower at the high end of the range that is best for your grass type.

7. Restrict excess fertilizing or too-frequent watering.

8. Keep your lawn healthy as the most conducive way to get rid of crabgrass.

When using a crabgrass preventer, keep in mind that this is a pre-emergence herbicide. To be effective, pre-emergent herbicides must be in place before germination occurs. Pre-emergence treatments are preferred because they are generally more effective for crabgrass control and less injurious to the turf grass that post-emergence treatments. In general, pre-emergence herbicides should be applied before soil temperatures reach 50 to 55 degrees Fahrenheit. This will allow the pre-emergent herbicide to form a barrier before the crabgrass seedlings emerge. Pre-emergence herbicides work by inhibiting the growth of young seedlings. These products do not eliminate established plants and must be applied before germination begins. Applications made very early in the spring have potential to break down before the end of the germination window and are, for the most part, not recommended. This is a particular problem in the three out of 10 years when late-season conditions are conducive for a second germination flush. Delaying pre-emergence applications in a very cool or dry spring would provide better season-long control because crabgrass germination is also delayed under these situations. Nearly all of the commercially available pre-emergence herbicides are very effective when applied properly. As always, read and follow label instructions when making herbicide applications.

For more information on crabgrass control as well as other common lawn problems check out NDSU Extension Publication H1553, "Home Lawn Problems and Solutions for North Dakota" available online at: or contact your local NDSU Extension Service office.



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