True, a big part of the problem was trying to grow at 44 lattitude with cheap greenhouses. We had temps hitting 115 in mid summer and lows in the 30s in october.. PM was definitely a problem. I've heard silica and neem oil sprayed twice a week in flower is a great PM preventative. A 1% hydrogen peroxide solution worked well for getting rid of the stuff, but the problem was it spread so quickly and was virtually uncontrollable. They had us doing foliars 2-3 times a day with a 2 gallon fogger on 260 plants.. It was dumb. Almost always used thrive alive green and yucca, some expensive crap from nectar of the gods. Terpinator was used in flower, which is just 4% soluble potash derived from potassium sulfate... Another expensive bottle of water from the hydro store.