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Invasive lawn grass - matt of rhizomes - Identify and recommend how to eradicate #573032

Asked June 22, 2019, 4:51 PM EDT

Thank you for response. Ref: Please refer to the 4 attached .jpg pictures. This grass was planted 20 years ago by a utility company next to the street and has taken over most of the lawn. In the spring it stays brown until 4-8 weeks after most lawns have turned green. The lawn had a very fine bladed grass (I suspect a fescue), and this “junk” grass has a wider blade, much like Kentucky or “playground” grasses. It spreads and grows from rhizomes which also make it very difficult to remove. One picture shows a sample rhizome I’ve taped to paper. Rhizomes remain 1-2 inches below the surface and probably extend several feet or more. Nodes are about an inch apart send a root down and a blade up. You can see a couple of small grass blades beginning to form. In an area the rhizomes cross each other forming a strong mat. The mat can be 1-2 inches thick and are very strong. Two of the pictures (#103-1020 and #103-1022) shows a section of mat, both the top and bottom. If the dirt is dry I can shake the mat and the brittle dirt will break apart and fall out. If you zoom in on the top (picture 103-0122) you can see several grass blades. My problem is to remove this junk grass and prevent it from growing back. I thought that Roundup and rototilling would do the job, but it only serves to cut the rhizomes into pieces and will probably grow back. Rototilling was probably a mistake. I need to find out how to kill it permanently so I can re-plant (probably a fine bladed fescue). If Roundup only kills the plant portion which grew it, possibly the rhizome and other nodes will grow later. I’m now spraying parts with a 2nd Roundup application. Can you identify the grass and suggest how best to eradicate it? Do I need a stronger commercial herbicide applied? Do I need to remove and replace several inches of dirt? I have a forest area in my back yard and if I dumped the old dirt there, would it die or lie dormant only to grow and cause future problems? I would appreciate any suggestions you might have. John Lilly <personal data hidden><personal data hidden>

County Minnesota

Expert Response

 

Thanks for the question. 

I suspect that your lawn has a heavy infestation of quackgrass.  In order to eliminate it – a task that will be neither quick nor easy – recognize that it spreads via two means:  rhizomes and distributed seeds.  You will need to attack on both fronts.

The first thing you should do is to be sure that you have quackgrass and not crabgrass.  The two are often mixed up.  The treatment strategies for the two are very different.  Take a look at the following sites for information about quackgrass as well as crabgrass:

https://www.whygoodnature.com/quackgrass-dont-call-me-crabgrass

https://www.thespruce.com/quackgrass-crabgrass-easily-confused-lawn-weeds-2153114

https://apps.extension.umn.edu/garden/diagnose/weed/grass/quackgrass.html

https://apps.extension.umn.edu/garden/diagnose/weed/idlist.html#Quackgrass

https://extension.umn.edu/weed-identification/perennial-weeds#quackgrass-844664

I am going to answer your question assuming you have quackgrass.  If you decide that you have something else, please disregard my response and get back to us.

For the immediate time other than trying to pull it up, there is not too much to do.  Even if you try pulling it up, you will leave behind root fragments that will generate more quackgrass.  You discovered this by your rototilling.  However, there is something you can do now in 2019 to greatly eliminate how much quackgrass you will see in 2020.

In late August to early September of this year,  quackgrass begins a very vigorous growth cycle.  At that time try to kill the quack grass with a product containing glyphosate, such as Round Up.   It is not clear to me when during the year you previously applied Round Up.  Unless quackgrass is actively growing (late summer), it does not readily take up the glyphosate and the underground rhizomes may not be completely killed.  In late summer, quackgrass should readily take up this herbicide, especially into its roots.  Under ideal conditions, this may kill the quackgrass before it releases any of its seeds.  However in order to avoid damaging any desirable turf, do this very selectively using a hand sprayer.  Try to direct the herbicide directly onto the quackgrass and avoid getting it onto surrounding grass.  Within a few days, you should see the quackgrass turning color and wilting.  This will be your sign that the quackgrass is dying.  If some quackgrass still looks unaffected, hit it again with Round Up.  You may have to repeat this tactic in 2020 as well.  Getting rid of quack grass is rarely a single year project.

If you decide to do some grass seeding this fall (late September),  wait at least two weeks after you apply the Round Up before doing so.

But having said this, you still may have had some quackgrass distribute seeds this fall.  So here is where a pre-emergent herbicide comes in.  In the spring of 2020, once the snow leaves your ground but before any greening up occurs, distribute some pre-emergent herbicide (for example, Preen) on the ground.  This should prevent any quackgrass seed from germinating.  However this same treatment may prevent germination of any grass seed you might have applied this fall but which did not immediately germinatel.  Additional grass seeding may be necessary next spring.  However wait at least for three weeks to do this after spreading the Preen.

Getting rid of quackgrass is not easy.  But with persistence and patience, it can be done.

Good Luck!!

 

An Ask Extension Expert Replied June 26, 2019, 4:54 PM EDT

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