Dieback of Azalea

Disease Information

Dieback

Symptoms and damage

Dieback is an important disease of hybrid rhododendrons in the landscape and is caused by the fungus Botryosphaeriadothidea. Azaleas with similar symptoms are more likely to be infected by the fungus Phomopsis species. Typically, dying branches (stem dieback) begin to appear on an otherwise healthy plant. The leaves die and can remain attached to the plant until late summer.

Usually a single branch on an established plant is affected. Scraping away the bark with a knife reveals a reddish-brown discoloration under the bark on dying branches of rhododendron. On azaleas the discolored wood under the bark appears chocolate brown.

Management

 Dieback is difficult to control on rhododendrons and azaleas in the landscape. The azalea varieties that are the least susceptible include: `Delaware Valley White,``Hershey Red,``Pink Gumpo` and ``Snow.` The following rhododendron varieties are considered resistant: `Boursalt,``Chionoides White,``Cunningham`s White,``English Roseum,``Le Barr`s Red,``RoseumTwo`and`Wissahickon.`

Reduce stress to the plants by planting in partial shade and watering during dry periods. Drought stress and freeze injury may predispose azaleas to infection. Avoid wounding the plant. Prune infected branches well below all discolored wood and dispose of dead plant material. Clean pruning tools between cuts with a dilute solution of household bleach (1 part bleach to 9 parts water) or 70% rubbing alcohol. For azaleas, fungicide sprays containing either thiophanate-methyl or mancozeb can be used. For rhododendrons apply a product containing a copper-based fungicide or chlorothalonil.

 



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