Is this bentgrass? If not, what is it?

Tekcor1May 23, 2012

I have this lighter colored grass that there are patches of in with my darker colored newer lawn. It is unaffected by a broadleaf weed killer,which leads me to believe it may be bentgrass. Can someone confirm this? If not, can you tell me what it is? My lawn is in Western Washington and the grass is in it's third season. The lighter colored grass has a wide, flat leaf compared to the rest of the lawn and there are several "clumps" of it around the lawn.


Also, I just put a new blade on my Toro push mower. I mulched for the first time, and after I cut the grass there are circles that are about the size of the blade all over the lawn. Does this have something to do with the new blade? Being unbalanced perhaps? Or is it because I mulched? I didn't have this issue with the old blade.


Here is a link that might be useful: Photos of undesirable grass and circles

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dchall_san_antonio(8 San Antonio)

Bentgrass creeps low along the ground. What you are looking at appears to be a bunch grass that grows in clumps. Before embarrassing myself with a guess, I would want to see what the seed heads look like. I am going to guess that you mow low enough that you have not seen seed heads. Someone else might recognize the grass right away.

No grass should be affected by a broadleaf week killer. At least they are not supposed to be. One exception is St Augustine which is affected by the 2,4-d products.

What kind of grass do you have? Usually we see perennial rye in the PNW. And how high/low are you mowing?

Is your new blade exactly the same design as the old blade? Or does it have a sort of S curve to it from the center to the tip? If it has a curve, you might have installed it upside down. If it is just flat and so was the old one, then it should not be the blade. Usually when you see scalping, 1) the mower is set too low, or 2) the soil surface is bumpy allowing the mower to raise and lower as the wheels fall in an raise up out of the low spots.

    Bookmark   May 23, 2012 at 8:30PM
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Thanks for the reply. I'm not sure exactly what type of grass it is. I got it from a local sod farm and it is a mixture of several types; it's what they use at the sod farm. I should have clarified that I used a broadleaf/crabgrass weed killer, so it rules out crabgrass.

As far as the lawnmower blade, the center of the blade has a "U" shape so it would be impossible to put it on upside down. I'm mowing at the same setting as I have the last two years, and I've never had this issue. Also, the lawn is only three years old, so the soil is still very even; there. I appreciate your input.

    Bookmark   May 23, 2012 at 9:10PM
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dchall_san_antonio(8 San Antonio)

How high/low are you mowing?

Is the shape of the new blade the same as the old one, including the U? I'm not sure how it would be impossible to reverse it. How did you put it on?

Three years is about the right time for some soils to fully settle. If yours is pretty level, then you are both lucky and can look forward to no surprises on that aspect. Still since it is causing the circles, there is something a little uneven about it. Really important to know how high the grass is after you mow. Can you go measure it quickly?

    Bookmark   May 23, 2012 at 9:16PM
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Looks like poa triv to me and your lawn looks like a fine fescue lawn.

    Bookmark   May 23, 2012 at 10:36PM
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Dchall, I should have been more clear about the blade. It is not U shaped from end to end, but rather along the width of the center. The metal that the blade sits against is also U shaped, so they spoon together. If you put the blade on upside-down then they would no fit together, rather one would be concave and the other convex. I also sharpen the blade regularly and am quite certain how to put it together. From what I've read putting the blade on backwards isn't uncommon so I'm surprised more manufacturers haven't go to a goof-proof design such as this.

My grass is cut at 2". I do need to interject though that I've been cutting my lawn at this height for three years and never had this problem. When I used the old blade a week ago it did not make these swirly marks. It obviously has something to do with the blade or mulching (or both), I'm just not sure what or how to fix it. I appreciate your suggestions.

Tiemco, I will research poa triv. Hopefully it is not terribly hard to get rid of, because I sure don't like how it looks in my yard!

    Bookmark   May 23, 2012 at 11:35PM
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Poa triv is not terribly hard to get rid of, it's damn near impossible.

    Bookmark   May 24, 2012 at 12:51AM
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Way to play with my emotions tiemco! I started reading your post and I went Yay! Oh wait, Aaaaaaahhhhhh! So the next question would be, of I dig up a sample, where do I take it to get a positive ID? Rather, what kind of business do I take it to? Once again, I appreciate the help even if it's bad news.

As for the mower, I took off the blade and balanced it and it was pretty unbalanced. I was quite surprised for a brand new blade, hopefully that solves my circles issue. I'll report back on that in a few days when I mow again.

    Bookmark   May 24, 2012 at 1:20AM
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Sorry for that Tekcor. Most universities that have a turfgrass program would be able to ID that for sure. You could also try your local extension service, or nurseries in the area, but they aren't always the best when it comes to grass. There are also a lot of sites on the web you can use to ID grassy weeds, and again I would start with Poa trivialis.

    Bookmark   May 24, 2012 at 9:13AM
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Not bentgrass for sure.

    Bookmark   May 25, 2012 at 9:06PM
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garycinchicago(Z5 Chicago IL.)

+1 Poa Trivialis

Adjust your lawn care regime so that you favor the desirable grass, not poa trivialis.

To encourage poa trivialis, mow short, irrigate shallow and often, provide shade.

To discourage poa trivialis, mow as tall as possible, hold off on irrigation until absolutely necessary (good grass shows tell-tale signs of drought stress) and provide full sun shine.

I know, easier said than done sometimes because of nature.

    Bookmark   May 26, 2012 at 2:16PM
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dchall_san_antonio(8 San Antonio)

I agree with gary and tiemco. After you said you hoped it was not hard to get rid of, I was already chuckling. Are you new to lawn care? Or new to reading about lawn care? There are worse weeds. The big problem is it is an ugly grass and not an ugly broadleaf weed. Selectively killing grass in grass is very difficult. Gary has the right idea. I have been able to get rid of nutgrass several times in my lawn by doing things that don't favor it.

Thanks for the additional info about your blade. I was going to suggest it was bent or one side higher than the other. If you raise your mower to the top notch, that problem might go away. You should raise it and I would go all the way to the top. Once it gets up there it looks great. Here's a pic of a fescue lawn from long ago. He wrote in with two pictures to thank the forum for the suggestion to raise his deck height.

He happened to be on a full organic program but that has nothing to do with deck height or your other issues.

    Bookmark   May 26, 2012 at 10:37PM
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