Powdery Mildew

Tried cukes last year in my indoor IBC set up. Hundreds of little (1/2") cukes, and then they plants started dying, and I ended up with powdery mildew in the gravel (pea gravel). Any thoughts or ideas on getting rid of it? I've heard baking soda, but to watch my chemical levels. My thought was to use one of the weed burners that attaches to a 20# propane tank. Thoughts or ideas?

Thanx