I always used to load my backpack sprayer with sevin and fungicide.
Mix the stuff 1/3 of what the bottle says.
It's WAY more than enough to do the job.
I spray my plants right before a rain. Always have. I always do it in the late evening, too.
That's cause plants open their millions of little mouths at night to breathe.
It allows the fungicide to enter the plant and become systemic.
It works 10,000 times better that way.
Then the next day it rains, medicine is in their system, and all is well.