Plant Disease Management Handbook

See:

Azalea (Rhododendron spp.) - Leaf Burn

Rhododendron - Sunburn

Summer drought combined with high temperatures and brief sun can scorch leaves.

Jay W. Pscheidt, 2019.

Note how the necrotic areas are all at the tips of the leaves.

Photo by Jay W. Pscheidt, 1994.

See:

Azalea (Rhododendron spp.) - Leaf and Flower Gall

Rhododendron - Witches' Broom

Note the reddened, enlarged leaves.

Photo by Stacey Fischer, 1987.

Image related to Rhododendron-Leaf and Flower Gall

Natural infection in the Cascades.

Bob Ross, 2009.

Cause Pestalotiopsis sydowiana, a fungus. A minor problem in the field but potentially severe in propagation. Leaf infection usually follows an injury such as sunburn, sunscald, or low temperature. Infection can be severe if leaves, on cuttings in cutting beds, are cut in half to reduce transpiration combined with heavy misting.

Image related to Rhododendron-Gray Blight

Brown areas develop on the leaf and small, black fruiting bodies form in the dead tissue.

Photo by Ralph S. Byther

Cause Seifertia azaleae (formerly Briosia azaleae) , a fungus that infects terminal flower buds through axils of the bud scales. Diseased buds may remain attached for 2 to 5 years. Insects and slashing rain spread spores to healthy buds. Plant types range in susceptibility with up to 90% of the buds infected on the cultivar Pink Pearl.

Image related to Rhododendron-Bud Blight

Fruiting bodies (synnemata) of the fungus can easily been seen.

Robin Rosetta, 2005.

Although not generally a problem, 20% of these buds were damaged.

Robin Rosetta, 2005.

See:

Azalea (Rhododendron spp.) - Botrytis Petal Blight

Cause Botrytis cinerea, a fungus. Growers observe that "purple" cultivars are more susceptible than others.

Note how the bent-over shoot has a gray area at bend.

Photo by Jay W. Pscheidt, 1991.

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.

See:

Rose (Rosa spp.) and hybrids - Armillaria Root Rot

Fir, Douglas and True - Armillaria Root Rot

Note the white plaques on the trunk in the center of this picture. White plaques can also be seen on the inside of the bark that was scraped off (right).

Photo by Jay W. Pscheidt, 2002.