Hello Carol,

Sorry, but I do not understand the reference to “thistle-like” grass. Thistle weeds are broad leafed and your pictures clearly show a clumpy broad bladed grass. It could be a tall fescue, an ornamental grass species or a forage type grass. Here is an article to help identify if it is a tall fescue: https://www.canr.msu.edu/news/pain-in-the-grass-tall-fescue

Which undesirable grass it is does not change your remediation options – you can remove it physically (dig it out) or chemically (by applying a non-selective herbicide such as glyphosate).

Anything that will kill off the undesirable grass will kill your desirable grasses as well. Once the undesirable grass is removed, you will need to overseed the bare spots. If you do not seed, you risk annual weed growth in the bare areas before the other desirable grasses spread in.

If you apply a non-selective grass killer (such as glyphosate) to kill the undesirable grass, be careful in the application of any grass/weed herbicide as it will kill your desirable grasses as well. Once the undesirable grasses are removed, you will need to seed the bare areas (likely next spring).

Here is an article on spring seeding of lawn areas: https://www.canr.msu.edu/news/tips_for_reseeding_lawns_in_the_spring

There are several excellent spring seeding references in this article: https://ag.purdue.edu/department/btny/ppdl/potw-dept-folder/2022/spring-seeding-lawns.html

Hope this helps.