How to Control Poa annua
The headline above is an ambitious statement. Poa annua germinates when the soil temperature gets down to 70 degrees or below in the fall. Poa annua germinates all winter long and once your fall seeding of fescue (our normal grass in this area) gets a a couple of months of growth on it, you could probably us a pre emergent like Barricade or several others to stop the Poa for the rest of the winter. That is too late since it germinates mainly in the fall when the soil temps are 50 to 70 degrees. I actually saw Poa produce seed heads in December 16th of 2018 in my driveway. Thats not just sprouts, but became mature enough to put on seed heads. Below is a photo I took.
The winter of 2018/2019 was a very bad year for lawns because it was so wet and constant hard rains that it was hard to establish the new grass seed. It seemed like every time I would put out some fescue seed we would have a hard rain and a week later, I would see my grass seed coming up a full city block at the entrance to Freedom Park tennis courts.
After doing a lot of investigating, I found that there is a fairly new material called Tenacity (expensive but a little goes a long way) which is a pre-emergent which does not harm fescue. If one gets Tenacity down in the soil early enough and accurately enough then Tenacity will keep the Poa annua from geminating. Tenacity breaks down after around 30 days so a second treatment can be applied at that time and then a third and final dose should be applied. I desided that I had a choice to either apply a third dose or save that last of three doses per year to later in the season as a pre-emergent for crab grass and other spring and summer weeds. I made the decision to apply the 3rd application in the fall mainly because most of the Poa annua germinates in the fall during October and November. I started a little later than I wanted on my application which was later September. That gave me about 90 days of pre-emergent control through mid to late January.
With Tenacity, you can only apply a certain amount per year and although it would serve as a pre-emergent from crab grass in the spring when the soil temperature reaches 50 to 55 degrees, my choice would be to put all three doses on in the fall. I would then follow up with another type of pre-emergent later in the winter to keep weed seeds from germinating.
When Tenacity is applied, it also is a post emergent for many broad leaf weeds and will kill them. Tenacity destroys the plants ability to make chlorophyll and the plant turns white and dies. It might take 3 weeks to do so, but it will be worth the wait.
It is important to use a good surfactant and a blue dye because over spraying the same place can damage the grass. Accuracy is important. Tenacity only requires 1/2 a teaspoon per gallon, so the small 8 oz bottle it comes in goes a long way.
Professional lawn care companies use this product for controlling Poa annua as well as some enlightened home owners who want a yard without Poa annua.
What I have typed above is what I did and I was very pleased in the results. I see traces of Poa on the edges of the lawn and on a place I did not spray around a tree that was covered in mulch. Turns out my mow and blow guy managed to rake off all the pine bark much I had around the tree trunks. Mulch shades out the Poa annua and that mulch got removed.
The surprising thing to me is that vertually all the broad leafed weeds were killed by the post emergent properties of Tenacity. There is one weed I have not been able to identify. It loves moisture and had it bad in the back yard. After I had sprayed twice I still saw this weed and was afraid Tenacity just did not work very well in controlling it.
Last week February 25, 2020 I could barely find a trace and that is what you see in the photo above. I did not have a lot of broad leaf weeds that were particularly visitable in the yard in the fall so I did not have a lot of white foliage from the spraying of broad leafed weeds.
To explain that a little further. Tenacity works as an existing weed killer by destroying the chloraphil in the plant. As the Tenacity does its job, the folage turns white for both broad leafed weeds and grassy weeds. Tenacity does not kill every weed. There are list on the Internet that list the weeds it controls, but there are additional weeds that it kills that are not on the recent list.