Bermuda grass vs Yarrow

I have a small central area in my garden that I seeded with yarrow two years ago to create a small yarrow lawn. Unfortunately, it is starting to be invaded by bermuda grass. I thought the yarrow was successfully competing with the bermudagrass, but lately it looks like the bermuda grass is starting to establish itself. Can anyone offer suggestions as to how to help the yarrow win?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file
Upload is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.