Annette I would add that you should be sure not to compost the (possibly) rusted leaves. If it is rust, that could be warm enough for it to overwinter in your area.
Secondly, epsom salts will help alleviate magnesium deficiency in your plants. In daylilies this is often seen as veining and streaking in the leaves. They have dark green veins with very pale green to yellow between them. It looks similar to chlorosis which results from iron deficiency. When I've seen this I just put a pinch of epsom salt near the base of the plant in question and water it in.
