In Tim Tompkins wrote:
A word of caution, Othenex contains triforine, this is a VERY
HAZARDOUS chemical, you MUST follow the directions on the label and
wear protective clothing: long sleeves, long pants, gloves and at
least a dust mask.

BS (and no, that's not short for black spot!). If Orthenex is harmful
then it's not because of the triforine component - probably more from
the insecticide in it.

Triforine has almost no safety warnings or concerns. You can buy it as
a concentrate or as a ready made trigger pack.

Having said that, I've found triforine only mildly beneficial on mildew.

The best preventative I know is foliar feeding, especially with seaweed
emulsion. The best remedy for me has turned out to be 4 weekly sprays
of one part whole milk to 5 parts water.

And DON'T trim the affected foliage. Cure it instead!