Hard to say. Might be a fungal issue brought on by the heat. Where are you located?

tj

Are these plants in pots or planted in the garden?

Heat and drought

and most importantly.. LACK OF WATER...

and rock retaining heat long into the night used as a mulch ... and i sure hope there isnt landscape fabric under the stone ...

ken

I mentioned about whether the plants were in pots or the ground because pots dry out even faster.

I'm in Minneapolis, and the hosta are in the ground. Paul's Glory has been there for 15 years, but we have had eight days in a row over 90 degrees, several days in the upper 90's. Blueberry Muffin was planted just last year. I have watered them now. The front yard is mostly shady, but in the mid-afternoon that area gets sun. I never noticed it before this year. I'll have to be more careful.

I am in MN too and I'm having the same issues with hostas I've never had burn before this year. Im good about watering... But i guess not good enough this time around.