Are there organic insecticides that I can use on my Rhododendrons?

I have recently discovered some damage to my Rhododendron's leaves some of the leaves look like there has been something chomping on the outer edges, and other leaves have turned brown in some areas. They also seem to be dried out in the brown areas and have some small dark dots underneath those leaves. I have also discovered ants crawling on the leaves. I know this can be an indication of Aphids, but I haven't seen any Aphids.

My shrubs are near a bird feeder and I would like to avoid using chemicals.