exobasidium

Exobasidium symptoms on Rhododendron spp. Photo: Bruce Watt, University of Maine, Bugwood.org

Updated: April 21, 2021

Key points

  • While very noticeable, Exobasidium leaf and flower gall will not threaten the health of the plant.
  • This problem is more common during cool and wet spring weather.
  • The first symptoms are swollen or puffy portions on newly expanding leaves, shoots, buds or flowers.
  • These areas turn into galls that range in color from green, silvery white, to pink or red depending on the part of the plant infected.
  • As these galls age, they develop a white surface growth which consists of a layer of reproductive spores.
  • Eventually, the infected plant part will turn brown and shrivel up into hard galls.

Management

  • Fungicide sprays are not effective for the control of this disease.
  • Prevention strategies involve hand picking the galls off before they develop the white sporulating surfaces.
  • This will reduce the incidence of disease next season.