Do you have an idea from this photograph what is going on with my rhododendrons? This happened last year and I sprayed them with miracle grow to give them more acidity and it seemed to work. This year it is a different story. Any suggestions are helpful and thank you in advance for your assistance.
Ingham County Michigan
Two things might be going on here. First, I'm wondering I you have taken a soil test recently to detemine the pH? As you probably know, rhododendrons love acid soil (5.5-6.0) and in Michigan, our soil pH ranges from very Acidic to very alkaline. Some yellowing tends to indicate that we need to apply an acidic fertilizer, formulated especially for rhododendrons. (Miriacid not miracle grow as you mentioned) The branch that seems most affected may also be showing symptoms of Phytopthera root rot. This disease especially affects Rhodondendron when planted in wet, clay soils. I would take a pocket knife and do some digging in the cambium around the base of this twig. If you are seeing brown tissue right below the bark, it would be a good indicator that you may have the rot present. Not to worry though--Prune out that stem close to the base and try to remove leaf litter and mulch in the general area of the trunk to try and let it dry out a bit. Remember that much of your plant looks really good, and try to remember that the new growth "tells the story" of how the plant is doing. Try this for a couple of seasons and see how it comes out of it. I think you are already on the right track! Have a great weekend.