I also have some common Bermuda in my St Augustine. It's in maybe 5% of my lawn, the majority of it is concentrated in two areas that recieve full sun. About 85% of my front lawn doesn't get enough full sun for Bermuda to be strong but it's great for St. A.
In my lawn, which I have only had for about a year, the Bermuda is embedded in two ways.
First there are solid chunks of it where it has established dominance. From about fist-sized chunks to as much as a square foot in one place wheee conditions changed that are now favorable to the Bermuda.
The other way it's crept in is the more challenging way, where it pops up in between the St. Augustine strongholds where there is a good amount of sunlight.
I plan to attack the areas where the Bermuda is bunched up first. I have lightly sprayed some glyphosate into the middle of some of these spots, careful not to hit the St. A. I plan to hand pick it, hit it with the trimmer, and overall try and weaken it over time while cutting around the St. A runners to try and give them favorable conditions.
I am also going to try and hit these Bermuda clumped groups with high doses of Atrazine. I will attempt one of the spots where it's more sparse and intertwined, but I want to be careful and not torch large patches of St Augustine in attempting this. Here are some pictures of my problem spots. My Atrazine just came in the mail today so I will be attempting this soon.
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