Good question.
The last time, I power washed off the start of any mold before I treated the canvas. It was fine at the time but comments on here afterward indicated that it wasn't a great idea. (Hey, I'm full of 'em!)
So, I think my plan will be to stop in at Gillan and see what they recommend. Perhaps some sort of a pre-treatment spray or something unless someone can verify that the washer will take the mold out with just the detergent?
I've got very little on there.