It looks like cherry leaf spot to me.

That's what I'm thinking. Any ideas for the type of fungicide that I should use to kill it? Should I apply the fungicide now or wait until the fall?

thanks

Treenation:

I have 3 tart and one sweet cherry. Sometimes I get leaf
spot too. I do spray with Captan. Captan is a preventative fungicide so it will do no good for the leaves already infected. It should keep the non-infected
leaves from getting the issue.

I have a few leaves with spot now, but since my cherries
are ripening, I will not spray until after harvest. Then I will spray with Captan or Chlorthalonil.

Do not spray chlorothalonil on your tree if it currently has fruit on it that you plan to be harvesting. Chlorothalonil is registered for use no later than shuck-split or can be used AFTER fruit is harvested to control
cherry leaf spot.

Captan can be used while you have fruit on the tree. Just
follow the directions as it does have a warning on when to stop spraying before harvest. I usually stop spraying
Captan about 15 days before I harvest my cherries.

If not controlled, leaf spot can weaken the tree if it gets
severe enough.

To add to that make sure the leaf clean up is done well.

Nothing will cure the affected leaves that I know of.
Immunox will stop it but if there's a chronic problem that's causing it, like staying wet with morning dew because of shade or lack of air flow (that fence?), it will continue coming back.
If that's the case I would try a different variety and/or a different spot.