What kind of invasive grass is making my lawn look bad and what can I do about it?

Invasive grasses can cause unsightly color variations in turf and can choke out your desirable grass.

In our little corner of the Pacific Northwest, most people start out with a rye grass, fescue grass or some combination of the two in their original lawns. Invariably, over time, invasive native grasses will begin to creep in. We just have too many open spaces, fields, pastures and waste areas where these native grasses get established and then spread. And, being native, they are better adapted to our climate, which allows them to out-compete the desirable grasses.

Here are a few of the most common ones and what can be done about them:

Poa annua

Probably the most common native and easily identifiable. This grass produces very distinctive small, whitish seed heads, even when mowed down as low as half an inch. Poa annua is also an annual grass, meaning it dies back each year and re-seeds itself. We have not found a really effective chemical control options so you can either live with it, which I highly recommend, or spray it out and re-seed/re-sod the areas. But be aware, this will be a yearly chore.

Bentgrass

It is most noticeable in drought stress, when it turns brown, or yellowish when we get frost conditions. This grass throws up a pulpy stem the grass blades sprout from. A “grass tree” if you will. Unlike many of our native grasses, this one will eventually die-out if it suffers through repeated years of summer drought stress. There are some products that supposedly will control bentgrass, but in my experience, they don’t work well. Another live with it or kill and replace. But be aware; if you choose to kill it, you must remove all the dead grass down to the dirt before replacing it or the new grass will not get well-established.

Poa Trivialis

This one is really unsightly, causing “bird nest” clumps of grass that grow fast and lays down. This one is definitely as kill it with glyphosate (Round Up) and do not let it spread.

Quackgrass

This one looks the most like a tall fescue in color and shape, but grows much faster, giving the lawn an uneven look between mowing. Nothing for it but glyphosate.

Crabgrass

Five years ago, if you told me you had crabgrass, I would have politely told you you were mistaken. Those days are gone and crabgrass is here to stay and spreading rapidly. This is a just plain ugly grass that will take over lawns and leave bare spots when it dies out each year. Unfortunately, it produces a lot of seed and sprouts back in the late spring the following year. Fortunately, we have a very effective two-application per year program that will eliminate crabgrass without damaging your good grass.

Nutsedge

This looks like a wide-bladed grass, but it is actually a sedge. This means it actually forms bulbs below the soil and, it allowed to grow long and tall enough, produces a seed. It is not bothered much by most turf herbicides, but there is a product called Sedgehammer that does a great job of controlling both yellow and purple nutsedge without harming your good grass.