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 grown 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. That’s 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 after another 30 days.
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 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.
Some 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.
Soil Temperature Is Critical.
I got a good thermometer from ???? and have been checking my lawn. I ended up finding 4 spots in the yard. The first was next to a cement plant container that gets sun pretty early in the morning and a lot more in the afternoon.
On September 18, 2019 we are close to drought conditions. The air temperature was 70.9 degrees and and I measured 82.6 degrees at the cement plant container mentioned above.
The second place I measured is under a young willow oak in the back yard, and it is shady and does not get much afternoon sun. The temperature there in the soil was 75.6 degrees. Photo below temperature was measured at the base of the metal bench.
The third reading was at the white Rabbit which is under a small red maple and does get afternoon sun but nothing in the morning. Rabbit location soil was temperature was 78.1.
The forth and last place is in the shade is mostly under a small japanes maple. Temperature taken at Gus’s Big Red Ball was 74.5 degrees
Since it is now the 25th of September several measurements from this location are down below 70 degrees. We had two days a week ago when the air temp at night got in the low 60’s, but since then we are seeing no rain and air temps in the high 80’s.
So, to me the Question is when I do I spray my lawn with Tenacity?
all for the day I will post more soon. Sept 25, 2019