Fescues (both fine and tall) are more susceptible to tearing than KBG, so if this is showing up more on the fescues, I think a dull blade is a likely prospect.

Can you post a closeup picture?

In addition to sharpening the blade, do you adjust it so you have the proper distance from the bedknife? That's apparently important and something I run across while trying to decide on getting a reel mower.

When grass gets cut it has to heal. Until it heals it has a greater chance of getting a lawn disease, especially if it rains within I think 24 hours of cutting.

Could be some of the grass is getting more damaged, could be some of the grass is resistant to the fungus while the other isn't? Do you see any dark spots on any grass blades?

OK, here are some pictures. The first is a range of sample blades from the lawn (the two on the left being healthy and the rest having some degree of browning). Then close-ups, and two wider shots. The one that is kind of C-shaped is what I had initially noticed, but now that I look closely I see some other patterns of browning too.

Thanks!

{{gwi:38953}}

Looks kind of like brown patch, a lawn diseases caused by fungus, except it doesn't have the dark rim that brown patch does.

The damaged blades are also much longer. Kinda looks like damage from the mower blade striking it but not cutting it, then striking it at a different location next time you mow and so on.

Only way to know what it is for sure is to take/send a sample to your local cooperative extension office and have them examine it under a microscope.

Might be time to sharpen or replace your mower blade. Frequent mowings with a sharp blade apparently helps to deter brown patch.