Oh I totally agree, you don't want over-use to create resistance. But that's not what's happening here.
Here's what was sprayed in 2016:
03/08/16 Kocide 3000 (Copper)
04/05/16 Immunox (Myclobutanil)
04/16/16 Monterey Fungi-Fighter (Propiconazole)
05/02/16 Monterey Fungi-Fighter (Propiconazole) & Triazicide
So last year my cherries got only one dose of Immunox. As you can see, I'd hit them twice with MFF as it's very good on Brown Rot which I've had more issues with that than leaf spot here anyway.
Similarly, here's what was sprayed this year - 2017:
02/19/17 Kocide 3000 (Copper)
04/17/17 Monterey Fungi-Fighter (Propiconazole)
05/05/17 Immunox (Myclobutanil)
05/16/17 Monterey Fungi-Fighter (Propiconazole) & Triazicide
So in the two years shown you can see I've used Immunox only once each year on the cherries. (I do two applications on apples for CAR)
But I just think for whatever reason the Crimson Passion bush cherries (mine at least) seemingly have a weaker immune system or something else going on, but it's not a resistance issue.
I don't have any other explanation for why they would be getting leaf spot while all other bushes don't.
The five CJ's have been here since '11 & '12
The two CP bushes have been here since '14
The two Juliet bushes went in in '16.
So the CJ's have had a chance to have fungicides applied to them for a longer period of time and they haven't shown any tendency to get leaf spot.
The Juliet's are short timers and still no leaf spot issues with them so far.
The CP's which sit in the same row/area seem to be leaf spot magnets under the same spray program. (Maybe they just need additional apps...)
Well, they did get an additional application a couple days ago after I plucked off the yellow leaves and picked up the ones on the ground...