I don't use systemics. Period.
I believe that a healthy system creates a healthy plant. I attack things that don't belong in that system with precision, and it seems to work just fine like that.
Systemics don't fit in that approach, and I want to stay away from those as far and as long as possible.
Unless, live fungi like Trichoderma viridae count as systemics. I use those systematically to combat mildew and other fungal issues.