D.M. Kenyon, G.R. Dixon, S. Helfer
Powdery Mildew is one of the most important foliar diseases of Rhododendron. Tentatively two pathogens are associated with this syndrome. These are possibly related to either Sphaerotheca pannosa (Rose and Peach powdery mildew) or Erysiphe cruciferarum which infects several host families. The latter infects the widest range of Rhododendron spp. and consequently is economically important in Britain (Watling, 1985).

Typical symptoms are a fine white coating of hyphae on leaves, stems and occassionally flowers. Fungal colonies are predominantly restricted to the leaf under surfaces with yellow chlorotic lesions visible on the upper surfaces. Chlorotic areas may later turn purple-black.

In the past 10–15 years the incidence of powdery mildew has increased rapidly causing dramatic damage to Rhododendron in both collections and commercial nurseries. The disease is widespread throughout Britain and has been identified in many major historic gardens. If unchecked these pathogens will permanently damage the fabric structure of important gardens and Rhododendron collections.

Current research is centred upon the development of an in vitro system for culturing of the host and pathogen. This will also allow experimental work to be carried out under controlled conditions.

Kenyon, D.M., Dixon, G.R. and Helfer, S. (1994). POWDERY MILDEW PATHOGENS OF RHODODENDRON. Acta Hortic. 364, 161-162
DOI: 10.17660/ActaHortic.1994.364.20

Acta Horticulturae