Sounds like the rhododendron rust disease caused by the fungus Pucciniastrum vacinii. This fungus invades rhodies and azaleas when they are planted near hemlock or become dry in the summer and more vulnerable to disease. First collect and destroy all infected foliage so the spores do not spread. After cleaning up around the plant spread a fresh layer of bark chips to seal in the soil fungi but don't pile bark up around the trunk of the rhodie. Feather the bark so it is very shallow near the trunk and an inch or two deep beneath the drip line or leaf canopy of the rhododendron. Then you can spray infected plants and the soil with wettable sulfur fungicide every 10 days in July and August following instructions on the fungicide. Make sure you do not allow your rhododendrons to dry out in late summer. Continue to remove any infected foliage and don't be shy if you need to prune back the shrub to get rid of rusty leaves - rhodies will recover from pruning and prefer to be pruned right after they bloom. As for organic products, some gardeners consider sulphur to be \"organic\" but to the scientific world that term is very misleading. (Water is a \"chemical\" called H2O and arsenic is a \"natural\" poison.) You can certainly try not spraying the plant with any fungicide and just cleaning up the infected foliage, adding a fresh mulch and watering more in the summer. Then let nature take her course. Keep growing and Good Luck, Marianne Binetti