KC Gardens

It’s time to control unwanted perennial grasses that crept into your yard

By Dennis Patton

The brown Bermuda grass has a shorter growing season than cool weather grasses like fescue.
The brown Bermuda grass has a shorter growing season than cool weather grasses like fescue. Provided.

While a lush green lawn is the pride of many suburbanites, others couldn’t care less. We all have to make choices about our preferred level of quality and efforts to achieve that look. For those wanting a high quality turf any invaders cannot be tolerated, while others may just say, “Well, at least it is green.”

Say the words zoysia or Bermuda grass and you will get very strong reactions, ranging from love it to invasive weed, depending on your desired outcomes. 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.

Cool season lawns are green for long periods of time, while warm season lawns have a short season. Those who like a better quality lawn 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 their more desirable lawns. Control can be achieved successfully if the proper steps are taken. 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.

Glyphosate works best if Bermuda and zoysia are actively growing. If growing well and lush, more chemical is taken up and pushed into the roots. A week or so before treating water the area well and skip mowing to develop more leaf surface area for absorbing the chemical. Stressed turf will not absorb the chemical and will reduce its effectiveness.

Once the unwanted grass is up and growing, spray the area to be treated and then wait for it to go to work. A follow up application can improve the kill rate and should be made 10 days to two weeks later to any areas still showing green. 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 one to two weeks and reseed. The ideal time to seed is around the first three weeks in September. 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 per Johnson County address, courtesy of a grant from Johnson County Stormwater Management.

Visit www.johnson.k-state.edu for details. Soil testing is provided by all local Extension offices on both the Missouri and Kansas sides of the state line.