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
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.
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.