Knowledgebase

How to treat/prevent poa annua #745504

Asked April 21, 2021, 1:36 PM EDT

Hello, I live in west Beaverton, a typical residential neighborhood. My lawn is tall fescue. Poa annua is a constant threat. I really try to keep the unsightly growth out of our yard, but it unfortunately invades some of my neighbors and spreads (presumably via wind) to ours. Two questions: Some of it has just appeared in my lawn and I fear (from experience) more of it is coming. What is the best current way to treat it once you have it? Can it be applied now? Second, what is the best way to prevent it from getting in? Thank you.

Washington County Oregon

Expert Response

I'm going to quote from the Pacific Northwest Handbook article on Annual Bluegrass:

"Selective preemergence and early postemergence control is viable with ethofumesate applied to pure seedling stands of perennial ryegrass. Ethofumesate is active on young annual bluegrass up to about the four-leaf stage. In mature perennial ryegrass, Kentucky bluegrass, or tall fescue, annual bluegrass can be controlled with three applications of ethofumesate in fall. Start in mid-October and reapply at 3- to 4-week intervals. Activity generally is not apparent after the first application, but yellowing begins between the second and third applications. In western Oregon, the death of the treated annual bluegrass may not be apparent until March, depending on the year. Kentucky bluegrass and tall fescue may be slightly injured or discolored. Some tests achieved 90% to 100% control after one series of treatments. Annual bluegrass may reinvade from seed once the herbicide dissipates."

I'm also going to link you to a response to a similar question from Alec Kowalewski, OSU's turf specialist, for a more detailed response.

For now, if you don't have too much, you can dig the poa annua spots up with a hand fork, or spot treat with glyphosate and reseed.  Then in the Fall you can try the above treatments.  I'm afraid there isn't really any way to avoid it getting into your yard completely.
Many thanks for this information. Please see the attached photo. Can you confirm it’s poa? If not, what is it and how should it be treated?
 
Bob
 
Sent: Wednesday, April 21, 2021 12:11 PM
Subject: Re: How to treat/prevent poa annua (#0015435)
 
The Question Asker Replied April 28, 2021, 1:30 PM EDT
Yes, that does look like poa annua (annual bluegrass) to me.
Another question for you: Is it risky for me to have our lawn aerated now when poa is present? I want to aerate the soil but I am concerned that it could contribute to greater spread of the hated weed. Please advise. Thank you again!
 
Bob
 
Sent: Wednesday, April 28, 2021 11:35 AM
Subject: Re: How to treat/prevent poa annua (#0015435)
 
The Question Asker Replied April 29, 2021, 1:31 PM EDT
This one is a bit tricky because while poa annua thrives in compacted lawns, it also finds footholds in disturbed areas (like the divots left behind by aeration).  So it depends on how compacted you think your lawn is and whether or not the pros outweigh the cons.  According to this article from Clemson, you can test lawn compaction by the following method:  "One way to determine if aeration is needed is by scouting the lawn. Take a screwdriver and probe the soil. If the screwdriver penetrates the soil with little resistance, then you probably don’t need to aerify. If it is difficult to penetrate the soil with the screwdriver, then you may need to aerify. Make sure the soil is moist when testing the areas, as dry soil can also be more difficult to penetrate. Inspect the overall appearance of the lawn and especially where the turf is thinning. Walk over the area and ‘feel’ the soil with your feet. If it feels like you are walking on concrete, then compaction could be a problem."

Quoting Alec Kowalewski again:  "If you plan to aerify (core cultivate) your lawn this process should be done in the spring during active turf growth, fall aerification often promotes annual bluegrass establishment."  So, if you determine that your lawn is compacted enough to warrant aerifying, then you should do it soon while it is still growing actively before summer.

Great information, thank you much.
 
Bob
 
Sent: Thursday, April 29, 2021 12:36 PM
Subject: Re: How to treat/prevent poa annua (#0015435)
 
The Question Asker Replied April 29, 2021, 3:49 PM EDT

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