Q. Yellow leaf growth on rhododendron
From your descriptions of the symptoms, this may not be due to a virus, but insead, this may be due to a low pH level in the soil. In rhododendrons and azaleas, a yellow color between the leaf veins is a clue. If the soil is not sufficiently acidic, the plant may develop iron deficiency, or chelation, which creates the breakdown of the green color between the leaf veins. You might want to have the soil tested and then apply a chelated iron or iron sulfate fertilizer. Holly-tone, easily available in garden centers, contains these elements and 4-6-4 fertilizer. You may have the soil tested at the Cooperative Extension Service. The Delaware County office address is 20 Paper mill Road; the phone number is 610-690-2655. The email address is DelawareExt@psu.edu. Good luck.