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Can anyone please help with the identification of this weed grass in my lawn? I live in the Pittsburgh area. It is like a lime green with purple stems (see Photos). The stems are thick and course. I have tried tenacity on this but no luck. I can not get a solid answer as to what this is. Any help would greatly be appreciated.enter image description here

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It looks like Elymus repens, common names "couch grass" (pronounced cootch) or "twitch" in the UK. In the UK the young stems can be light purple coloured but not usually as dark as in your picture, but I think it is the same species.

The bad news is there is no selective herbicide that will affect it. You could try a gel formulation of glyphosate or similar weedkillers. Even non-selective herbicides may take up to 3 weeks to kill it, and may need repeat applications.

The only non-chemical way to eradicate it is completely remove the roots (which are actually rhizomes, not roots). If you leave any root at all in the soil it will regrow.

The "nuclear option" of completely removing the turf layer and burning it (or disposing of it if off-site) and then frying any remaining roots in the soil with a flame-thrower will probably work, but is not 100% guaranteed. This thing is a survivor.

Its only "good" quality is that it does not have fertile seeds, so it only reproduces and spreads vegetatively - but that is little consolation if you want to get rid of it.

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  • If it's Elymus repens, then all of the plants should be connected via lateral roots (like quickgrass is). Is this the case with your weedy grass? See photo here: nps.gov/kova/blogs/images/1459493.jpg – Jurp Apr 21 at 15:54
  • @Jurp Not necessarily. If whoever laid the lawn tried to get rid of it by shredding the roots and burying them, each bit of root will be a separate plant! The old generation gardeners in the UK used to say that if you pulled up a piece of twitch, hung it the wall in your garden shed for seven years, and replanted it, it would grow again. – alephzero Apr 21 at 18:08
  • true, but the poster did not say that this was new turf. The poster could also have detached each plant from the lateral root when pulling them. The rhizomacity (to coin a word) of the grass is key to the ID. Not saying you're wrong but trying to prove you're right so that we can increase the knowledge base on the site. – Jurp Apr 21 at 18:12

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