CO-Horts

CO-Horts

Thursday, August 20, 2015

My Lawn is Turning Red?

Tony Koski, Extension Turf Specialist

Rough(stalk) bluegrass (Poa trivialis) will turn purple or
red when it becomes heat-and/or drought-stressed,
and then brown when completely dormant.
It’s been an interesting year for lawns. The cool wet spring gave us perfect growing conditions for bluegrass and other cool-season grass lawns – and perfect conditions for some diseases we don’t normally see here. Then it turned hot and dry, causing Ascochyta leaf blight to break out in epidemic proportions. I’ve written about yellow lawns and brown spots. Now we are getting calls and emails about red and purple spots in lawns.

Rough bluegrass turns brown when completely dormant.
While it looks dead, it will revive itself when cooler
weather returns in the fall.
The red grass people are seeing is rough(stalk) bluegrass (Poa trivialis) reacting to the very hot weather we’ve had the past couple of weeks. This cool-season relative to Kentucky bluegrass likes hot weather even less than our bluegrass lawns do – so it will often go dormant when we get long stretches of 90+ degree weather. Most often it just goes from green to brown, but it sometimes turns a bright red or purple before browning out. These red grass plants may have stopped producing chlorophyll in advance of becoming dormant (a “smart” thing for a plant to do), leaving red pigments behind – giving the plant a red appearance. Or they are producing extra xanthocyanins and carotenoids (red, purple and pink colored pigments) to protect the leaves from excess light (kind of a sunscreen that the plant produces to protect itself). Either way, the Poa triv patches in some lawns (usually in the hottest, sunniest parts of lawns) take on a reddish or purple cast – before turning a dead-appearing brown.

While it may appear to be dead, dormant Poa triv
will come back from live stolons on the soil surface. You
can find these green stolons when you dig down into
the patches of dormant, brown grass.
In spite of the dead appearance, the grass is only dormant. When cooler weather returns, it will green up again. Triv will often go dormant when it’s hot, in spite of generous irrigation. It’s not a drought-induced dormancy, but rather a heat-induced one.

This happy, green Poa triv is growing in a shady spot
just a few feet away from the brown patch pictured
above. It is aggressively and successfully crowding out
the original grass - turf-type tall fescue.
When you have a lawn full of Poa triv, you either learn to love it (or at least tolerate it), or you kill it and reseed or re-sod. There is no selective herbicide that will eliminate this weedy grass without harming the bluegrass or ryegrass in the lawn. Poa triv spreads easily and quickly by creeping stolons (runners) to form large patches - especially in lawns that are kept on the wet side. Shade favors its growth, but it can grow quite well in full-sun (but is more likely to go dormant in the sunnier parts of lawns). It is an aggressive, smothering grass under optimal conditions (wet, cool, shady), but less aggressive in drier, sunnier lawns.

I’m hoping for some cooler, wetter weather that will give us healthy, GREEN grass again.

5 comments:

  1. I have such a hard time distinguishing this grass from fine fescue--based on your last blog photo, I would have said it was fine fescue. Fine fescues also don't like hot weather, so they can turn brown. Since they look like cousins, do you have any suggestions for ID?

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  2. They are confusingly similar in appearance. I like to pull on the grass and see if (or how) it comes up? Poa triv forms stolons (runners) on the surface of the soil, so it will peel up relatively easily. Fine fescues will be more firmly rooted and are not easily pulled up. Poa triv also has shinier green leaves and a taller ligule than the fine fescues - if you want to look that closely! :)

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  3. You guys have the most fun blog. Everthing from red grass to cemateries. Now I know what I have in my lawn. My lawn care company keeps telling me its crabgrass or quack grass. I will show this to them and tell them to read you blog so they can do a better job with their customers like me.

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  4. Susan with red grassAugust 22, 2015 at 9:25 PM

    I knew it wasn't crab grass. That's what my hubby kept telling me it was. And the guy next door agreed with him. Like they know anything, right? I found pictures of crab grass on the web, and what is in our lawn did't match the pictures, so I knew it wasn't crab grass. But I didn't know what it was. Big patches of the lawn are turning red and purple. I took some to our garden center and they said it was bend grass, but I couldn't find that on the web anywhere. When I did a search for lawn turning red, i foudn something called red thread but that is a spring problem when it is cold and its so hot now that didnt make sense. Then I found your article which is exactly the problem we have in our lawn. You describe it perfectly and the pictures are just like the red grass in our lawn. I showed my husband and he agrees with me, but not happy that I figured it out. typical. So bummer that I really can't get rit of it. But so happy that I can tell hubby and knowit-all guy next door they were wrong LOL. Thanks for your great article that made me look smart

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  5. Poa triv is turning my lawn red right now! I didn't know what it was, so thanks. With all the battles I've had over the years with my grass, I sometimes fantasise about paving it over but the kids would miss out on the play area. It would save me a lot of heartache, though.

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