It looks exactly like rust. Eagle 20 or Bayer disease control are the only things that helps. Once you get rust in your room its almost impossible to get rid of. I have bleached(12 oz a gal) and used ammonium chloride between grows and it always comes back in the end. What I have been doing is spraying once in veg once day 1 flower and once 1 week into flower. I normally see the 1st signs at day 35 of flower. It is a very slow moving fungus. What I have observed it only effects fan leaves. I have not seen any major decrease if any at all as long as you control it. Keeps your nutes a little higher than normal. As soon as you start to flush the whole room will look like Autumn in a few days.