Dimethylsulfoxide, it acts as one of the worlds weirdest materials as it's one of the very few relatively safe chemicals that doesn't care whether there's a cell membrane, cell wall, or chitin armor.. It passes through it all.. And it takes everything with it.
Lab technicians get it on their hands sometimes, and some of them report a taste of garlic in their mouths, mwaning that it travels rapidly throughout the body.
If drugs don't penetrate the skin, add some dmso and they will if they're soluble in it. Most fungicides are.
But dmso alone as a "paint on" treatment killed external rust pretty easily. It is a temporary fix when not coupled with a fungicide. But it might be a permanent fix when coupled with fungicides, as they can essentially get to the core of the infection and kill it from the inside.
It's cheap, on it's own not dangerous, and plants have a decent tolerance to it. But do wear gloves and eye protection, because it will literally pull soap residue from the outside of your hands, to the inside.
