Branches die at any time. Shoots usually die during growth flush. Factors Favoring Infection and Spread of Dieback Phytophthora dieback is favored by hot, wet weather during the summer months. The fungus is spread from infected plant debris on the container base and between plants by spores in splashing water. Free water on the leaves is needed for infection by the spores.
Infection occurs on the lower surface of expanding new leaves.
Nurseries where rhododendron are grown under shade and irrigated by overhead sprinklers provide ideal around plants often occurs in nurseries using pine bark or plastic as a container base and increases the spread of the fungus by splashing. Excessive use of nitrogen fertilizer, which increases plant succulence, particularly during August, increases plant susceptibility to Phytophthora . Phytophthora dieback is not a common disease problem in the landscape. Purchase only plants that do not show Phytophthora dieback or root rot symptoms. Remove and destroy all severely infected plants and plant debris promptly.