WHAT CAUSES THE LEAVES ON MY WYSTERIA BUSH TO GO RUSTY

By rusty, do you mean a rust coloured deposit on the leaves? If so, its' got rust, a fungal infection, so get yourself a fungicide to treat it with. If they flower, it's about May time, but if yours is a young plant, you will be waiting some years.

A fungicide may not be that effective this late in the season. Make sure you rake up and burn the diseased leaves and start to spray with a systemic fungicide early next summer.