Q.Will Regular Grass Invade Feather Grass?
I have fight it for two summers. It looks like regular grass is invading my reed feather grass? Any suggestions?

Certified GKH Gardening Expert
There are countless types of grasses, and it would be hard to identify from the photo. Many do grow to be invasive, and it looks to be an issue, here. Unfortunately, this may be a permanent problem. Aside from killing off everything in the area, the grass will, likely, persist.
You can some help with your local extension service. Taking samples to them may get you an ID, which might open up the possibility of using a selective herbicide.
https://www.gardeningknowhow.com/garden-how-to/info/what-is-extension-service.htm