I know because I did it last week, fortunately only one girl burned like that. I'm going with a systemic ASAP, I'm sick of all this God damn foliaring.
I know this is old, but so am I, lol!
Did you ever find a systemic?
I've been using cal/phos from eggshells and vinegar, amino acids, and fulvic ala Harvey Smith.
It works great when the grow room temps are high, but I also think higher temps slow down pm anyway.
Didn't see any all summer, but as soon as temps got into the 60s, it started cropping up again. RH is 30-45%.
I grow in a crawl space, so it's impossible to completely clean, plus have to keep fans moving air.
Green Cure works for a few days, and I can keep the pm under control, but I want to be rid of it, and sick of foliars, too, lol!
Just found some SM-90, anyone had any luck with that?