poa annua control - Ask Extension
Last summer I replanted my lawn by killing it with glyphosate, dethatching it, reseeding with an Oregon certified perennial ryegrass mix, and giving i...
Knowledgebase
poa annua control #798418
Asked June 29, 2022, 1:45 AM EDT
Last summer I replanted my lawn by killing it with glyphosate, dethatching it, reseeding with an Oregon certified perennial ryegrass mix, and giving it a light cover of sawdust. Before the summer was over I had several spots of annual bluegrass, and this year it is just getting worse. What can I do about it. Do you recommend any post- and pre-emergence herbicides? Thanks.
Marion County Oregon
Expert Response
Hello,
Welcome to Oregon and the Pacific Northwest! The annual bluegrass is in your seed bank.
Unfortunately, you cannot prevent annual bluegrass from taking over your lawn, you can only delay the process. How do I know? There are no golf courses in western Oregon and Washington that have been successful keeping out annual bluegrass despite some having over million dollar budgets. They have all converted to nearly 100 percent annual bluegrass in spite it never being planted. Annual bluegrass is the only grass that will produce seed heads even though it is being mowed regularly. The seeding even occurs on golf course putting greens that are being mowed at 0.110 inches seven days a week.
There are a few things you can do to delay it. First, apply enough fertilizer to keep your lawn dense throughout the year. This especially applies in the winter when temperatures decline, growth slows, and the soil is wet. Second, mow your lawn at 2 – 2.5 inches regularly. Twice a week is better than once a week especially in the spring and fall. If the Poa annua is flowering, retain the clippings (i.e. bag them when you mow) and discard them in a mulch pile or some other place. Third, irrigate your lawn regularly (2 - 4 x per week) in the summer to keep your lawn dense.
Fourth, apply a pre-emergent herbicide in the spring and fall. Some examples of herbicides that you can apply to your lawn are Dimension, Barricade, Crew, or Pendimethalin (e.g. Pendulum). These products come in granular formulations so you can apply them with a drop spreader.
Lastly, to kill existing annual bluegrass, you can spray Prograss herbicide in the fall. However, you need to make 3 - 5 applications every year with each application spaced 3 - 4 weeks apart. Unfortunately, this product is for commercial use only and you would need to hire a licensed pesticide applicator to apply it. Needless to say, this would be very expensive. Some annual bluegrass plants will not be affected by these applications (they have resistance) and they will produce seed and offspring that will also be resistant. Over time, the resistant populations will grow and Prograss will no longer be effective.
Another alternative is to spray out the individual plants with Glyphosate (e.g., Roundup) and reseed the dead patches with perennial ryegrass. Any plant that glyphosate gets on will likely die, so be careful if you go this route. Keep in mind if you are reseeding and you are also applying a pre-emergent herbicide, you will need to wait until the seed germinates and grows for a month before applying the pre-emergent herbicide. Read the label for exact timing after seeding.
My recommendation is to let your lawn convert. Annual bluegrass can produce a really nice lawn, albeit a little lighter in color. If you have doubts, visit your local golf course and see how nice the turf is. Undoubtedly, it will be predominantly annual bluegrass.
Good luck.
Welcome to Oregon and the Pacific Northwest! The annual bluegrass is in your seed bank.
Unfortunately, you cannot prevent annual bluegrass from taking over your lawn, you can only delay the process. How do I know? There are no golf courses in western Oregon and Washington that have been successful keeping out annual bluegrass despite some having over million dollar budgets. They have all converted to nearly 100 percent annual bluegrass in spite it never being planted. Annual bluegrass is the only grass that will produce seed heads even though it is being mowed regularly. The seeding even occurs on golf course putting greens that are being mowed at 0.110 inches seven days a week.
There are a few things you can do to delay it. First, apply enough fertilizer to keep your lawn dense throughout the year. This especially applies in the winter when temperatures decline, growth slows, and the soil is wet. Second, mow your lawn at 2 – 2.5 inches regularly. Twice a week is better than once a week especially in the spring and fall. If the Poa annua is flowering, retain the clippings (i.e. bag them when you mow) and discard them in a mulch pile or some other place. Third, irrigate your lawn regularly (2 - 4 x per week) in the summer to keep your lawn dense.
Fourth, apply a pre-emergent herbicide in the spring and fall. Some examples of herbicides that you can apply to your lawn are Dimension, Barricade, Crew, or Pendimethalin (e.g. Pendulum). These products come in granular formulations so you can apply them with a drop spreader.
Lastly, to kill existing annual bluegrass, you can spray Prograss herbicide in the fall. However, you need to make 3 - 5 applications every year with each application spaced 3 - 4 weeks apart. Unfortunately, this product is for commercial use only and you would need to hire a licensed pesticide applicator to apply it. Needless to say, this would be very expensive. Some annual bluegrass plants will not be affected by these applications (they have resistance) and they will produce seed and offspring that will also be resistant. Over time, the resistant populations will grow and Prograss will no longer be effective.
Another alternative is to spray out the individual plants with Glyphosate (e.g., Roundup) and reseed the dead patches with perennial ryegrass. Any plant that glyphosate gets on will likely die, so be careful if you go this route. Keep in mind if you are reseeding and you are also applying a pre-emergent herbicide, you will need to wait until the seed germinates and grows for a month before applying the pre-emergent herbicide. Read the label for exact timing after seeding.
My recommendation is to let your lawn convert. Annual bluegrass can produce a really nice lawn, albeit a little lighter in color. If you have doubts, visit your local golf course and see how nice the turf is. Undoubtedly, it will be predominantly annual bluegrass.
Good luck.
