Good morning!

How long have you had it on your grass? Here is a great fact sheet from CSU on ascochyta if you haven't read through that already. Can you send some photos over?

Before using a fungicide (pending how long it has been on your grass) I would start with some cultural controls. Cleaning your mower blades in-between each mow, bagging the clippings so they do not spread and making sure your blades are sharpened will help. Also make sure to check your irrigation to ensure it is running efficiently.

There are not a lot of fungicides out there for treatment since ascochyta is found on the blades of the plant not the crown or root. Do you use a lawn company? If it has been persistent for a while and has a huge spread, I would reach out to a turf grass company to see if they would be able to treat it. 

Hopefully this helps!

Rachel