KC Gardens

Controlling unwanted warm season grasses

Tip of the Week

Say the words zoysia or Bermuda grass and you will get very strong reactions, ranging from “love it” to “invasive weed!” These warm season grasses are yard staples in the South. But for us Northerners, we tend to prefer the cool season grasses, such as bluegrass and tall fescue. We enjoy their green color for long periods of time, while we despise the short season. We value the feeling of walking barefoot through the soft grass. And most of all, we dread the runners of the warm season grasses that invade our gardens or creep in from the neighbors.

Each year our office fields a number of questions from people wanting to rid their lawns of patches of these grasses that have engulfed the more desirable lawns. Control can be achieved successfully if the proper steps are taken. Luckily, now is the time to start the process of eradicating these “weeds” so that a new lawn can be established this fall.

So how do you control Bermuda grass or zoysia that has invaded a cool-season lawn? Research conducted at K-State showed that glyphosate (Round-up, Kleen-up, Killzall and Kleeraway) are the best herbicides for the job. Glyphosate is a nonselective herbicide and will kill everything — including tall fescue or Kentucky bluegrass. That means you will need to reseed treated areas.

In the study, researchers applied glyphosate on July 15, and again on August 15, on warm-season grassy plots that were more than 15 years old. Now, in the real world, it does not have to be on that exact date. The recommended time for application is on or around these dates.

Glyphosate works best if Bermuda and zoysia is activity growing. If it is growing well and lush, the more chemical is taken up and pushed into the roots. A week or more before treating, water the area well, maybe lightly fertilize, and even skip a mowing to develop more leaf surface area for absorbing the chemical.

Once the unwanted grass is up and growing and the lawn is not drought stressed, spray and then wait for it to go to work. Spray again in about a month if there is any green left. Another tip to help increase control is to mow the lawn about two weeks after the first application. This removes the dead growth so that it does not impede the second application from reaching the newly emerging shoots.

After this second application, you will need to wait about two more weeks and reseed. If you follow this timetable, it will have you reseeding around the first week in September, which is the best time to establish a new lawn from seed. While waiting to reseed, you could have your soil tested to determine your pH levels and fertilizer needs. Johnson County residents can get one free soil test, courtesy of a grant from Johnson County Stormwater Management. Visit www.johnson.ksu.edu for details.

So there you have it — the tricks and schedule to rid your lawn of the unwanted invaders.


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