My rhododendron is a new plant but after 6 weeks the leaves are turning a very light green with a brown/tan residue on them. I have 2, both planted the same and the other is ok.
Certified GKH Gardening Expert
Check whether your plant's symptoms match anything in this article:
Is the residue you mention something that can be brushed or washed off? If so, this could be powdery mildew. Unlike in most plants, powdery mildew in rhododendron appears brown or tan in color. Here is more information:
The pale green leaves are probably what's known as "chlorosis". This is often a sign of nutrient deficiencies or of soil pH that is too high for rhododendrons. Here is more information: