I use something called mancozeb. It may or may not contain copper. One source I read says it contains manganese and zinc, another said "inorganic copper," whatever TF that is.
I have read some growers stating concerns that the copper could turn into something toxic as a result of combustion, but that's all I know. I chose mancozeb because I read that it is used to control fungus in tobacco, recommended by the ag experts at the University of Kentucky.
I found a list of fungicides approved by California for cannabis. It's almost all "natural" oils like neem, rosemary, cloves etc. No metals on the list, far as I can tell.
I try to use mancozeb as seldom as possible, after rains to prevent powdery mildew. I can't really say if it works or not. I've had some PM on plants recently, mainly on a strain that I think is kind of vulnerable (Godfather Purps). I gave one plant a good soaking but two days later it still appeared to have the white powder on the leaves... but that could be dead mildew for all I know.
Lately I've been more aggressive about just cutting off foliage that has PM. It mostly attacks the leaves, and it attacks AFTER a rain, according to what I've read and seen on my plants. In fact, I read somewhere that just spraying plants with water might get rid of it or at least push back against the infestation. Apparently PM does not like A LOT of water, just dampness.
