Great thread. I never thought of potassium phosphites in the same way as an overused fungicide that allows the disease to show resistance. In turf, phosphites are used to control Colletotrichum and Microdochium. Because of the amount of commercial fertilizers containing phosphite, our national governing body just announced that all phosphites must be registered as a fungicide. Will raise costs but will hopefully allow their effectiveness to increase with less, more targeted use. 3 year grace period.