Rhododendrons infected with Phytophthora ramorum
I have 5 rhododendrons that are more than 15 years old. Over the past 5 years, they have slowly developed yellow and brown leaf spots and odd colored stem growth. I've been removing the leaves, have embellished the surrounding soil and nothing helps. Four of them are close together. However, one on the other side of the house now has a few yellowed leaves. What should I do? Remove them? I read online that we should burn all plant material. Help!
This is not Phytophthora ramorum (Sudden oak death.)
This is a fungal leaf spot (See our diagnostic chart: http://extension.umd.edu/sites/extension.umd.edu/files/_images/programs/hgic/Publications/HG51_IPM_A... Removing infected leaves, fallen leaves, can be helpful. You can put the leaves in the trash.
Your variety of rhododendron may be particularly suceptible to leaf spots. The shrubs look very sparse and overgrown. You may get a better looking plant if you do a renewal pruning in the early spring. In a couple of years, you should get a more compact and fuller plant.