Powdery mildew experiment

I'm first time gardener and everything is new to me. 

For example - powdery mildew. I have some cuces on a very sunny spot on my deck, I thought I can be the perfect place for them, yes they're starting to grow very nice little cuces, but
those white spots!

Cuces in a more shady garden do not have those problems.
I guess it is powdery mildew. So today, may be late, I began an experiment - I mixed 1 tsp baking soda, 1 tsp dish liquid, 1 tbsp fish emulsion in a water and sprayed the leaves on top and bottom.
Let's see....