Rhododendron-Botryosphaeria Dieback

Latest revision: 
March 2024

Cause Botryosphaeria dothidea, a fungus, that has been found by the OSU Plant Clinic a few times on samples from coastal areas of western Oregon. Infections occur through wounds. Members of the Botryosphaeriaceae fungi can occur as endophytes, pathogens, and saprophytes on a wide variety of woody hosts. Many are latent fungal pathogens that cause no symptoms under normal conditions. However, disease symptoms can occur when plants are water-stressed such as under extreme heat fluctuations or during droughts. Some species of these fungi grow well in high temperatures and at water potentials much lower than what their plant hosts can tolerate.

Symptoms Tip necrosis of leaves and dieback of twigs was found in Oregon. Leaves on affected branches become dull green, turn brown and then roll downward, parallel with the stem. These dead leaves generally remain attached to the stem. The vascular cambium becomes dry and brown and may, at first, occur on only one side. In cross section the discolored and dead wood forms a wedge shape. Symptoms may spread down the stem encompassing whole branches and, sometimes, whole bushes.

Cultural control

  • Plant cultivars adapted to the area grown.
  • Remove and destroy all dead and dying branches below the discolored wood.
  • Avoid late season fertility that produces lush growth into the late fall.

Chemical control There has been no research on chemical control of this disease.

Reference Linderman, R.G. and Benson, D.M. 2014. Compendium of Rhododendron and Azalea Diseases and Pests, 2nd ed. St. Paul, MN:APS Press.