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Tackle crabgrass, Bermuda grass invasions with a few methods

Q. When should crabgrass preventer be applied?

A. Forsythia is our cue to apply "crabgrass preventer," or more correctly crabgrass pre-emergent herbicide. The optimum time to apply this herbicide is typically when Forsythia starts to drop its blossoms.

That's about the time that the soil is warm enough for seed germination.

However, our prolonged cool weather this spring may have delayed soil warming and probably has delayed germination a bit. Depending on the chemical and the time of application, the effectiveness of the pre-emergent herbicide chemicals may dissipate before the crabgrass seed germinates and starts growing. If you're on your toes and note crabgrass starting to grow, there are some herbicide products that will kill the plants after they emerge but when they are still small and young.

Why doesn't my crabgrass preventer ever work?

When people ask me about crabgrass preventers, I've learned to ask how they know they have a crabgrass problem. Many folks think the dastardly lawn invader plaguing them is crabgrass, but often Bermuda grass is the real culprit. It comes back each year from roots and rhizomes. Crabgrass comes up each year from seed. At this time of year, you can pull up the tough wiry rhizomes of Bermuda grass and may note small sprigs of green just starting to emerge along the rhizomes. Crabgrass preventers have absolutely no effect on Bermuda grass because it's a perennial warm season grass. Before applying a "preventer" product, make sure crabgrass is the weedy grass that's invading your lawn.

Q. You're right, I have Bermuda grass. What do I do about it?

A. Controlling Bermuda grass in your lawn is close to impossible. There are no chemicals that you can put on your grass that will outright kill the Bermuda grass and not hurt the desirable lawn grass. If there is only a patch here and there, you can kill the Bermuda grass by spot treating it with glyphosate. This is most effective when applied in late summer when the Bermuda grass starts to flower. If a large percentage of your lawn area is infested, you have two choices. One is to live with it. The other choice is to renovate your lawn, killing all the grass and starting your lawn over again.

Q. Whoa! I've heard there's a chemical that you can apply to the lawn and selectively kill the Bermuda grass and not the Kentucky bluegrass. What about this?

A. There is a Bayer product containing fenoxaprop that will suppress the growth of Bermuda grass growth. Directions for the product indicate that to achieve Bermuda grass control you will need to apply the products on a monthly basis (during the growing season) for one to two years.

Failure to make timely treatments on the prescribed schedule would mean a failure to effectively suppress the Bermuda grass. Hopefully, within the next several years there will be some new, more effective products that may help us our Bermuda grass problems.

Q. When should I fertilize my lawn?

A. In order of importance, the optimum times to fertilize your lawn in our region are September 1, November 1-15, May 1, June 15.

* Marianne C. Ophardt is a horticulturist for the Washington State University Benton County Extension Office.

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