Plant Disease Management Handbook

See:

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

Notes: Armillaria root rot is a problem mostly in the forest. It could also be a problem in the landscape if trees are planted in new home sites recently cleared of native vegetation. Avoid wounding roots and overwatering in landscape settings.

Wood decay in this sample was due to Armillaria.

OSU Plant Clinic Image, 2017.

See:

Dogwood (Cornus spp.) - Leaf Spots

Image related to Dogwood (Cornus spp.)-Anthracnose

All the reddish spots on these flower bracts are due to anthracnose.

Photo by Ralph S. Byther

Many leaf lesions can disfigure leaves and stunt growth when disease pressure is high.

Jay W. Pscheidt, 2010.

Leaf blight due to anthracnose on this Cornus kousa.

OSU Plant Clinic Image, 2010.

Notice the twig dieback from this fungal disease. Note the dead leaves.

Photo by Everett Hansen, 1999.

Cause Sclerotinia sclerotiorum is a fungus that overwinters as small black structures (sclerotia) attached to decomposing infected plant portions. Sclerotia may survive more than several years. After a moisture-conditioning period of at least 70 days, they produce a small, stalked, cup-shaped fruiting structure (apothecium), which releases spores into the air. Spores may infect blossoms and senescing leaves. After colonizing, the fungus can invade healthy parts of the plant.

Cause The soilborne fungi or fungus-like microorganisms, Fusarium spp., Pythium spp., and Rhizoctonia solani, may attack before, during, and after germination. In the Pacific Northwest, Pythium spp. are the major cause of pre- and post-emergence damping-off of young dill seedlings. Pythium is favored by cool, wet soils.

Cause Alternaria species. These fungi survive in residues of affected crops including carrot, parsley, celery, and parsnip; they also may be seedborne. Spores move by wind and water.

Symptoms Seedlings and older leaves are more susceptible. Yellow spots develop and centers may be coated with sooty black spore masses.

Cultural control

Cause Dasheen mosaic virus, a rod-shape potyvirus. It can be transmitted by aphids (nonpersistent), mechanically through infected sap, and by vegetative propagation. It infects many members of the Araceae family including jack-in-the-pulpit, caladium, philodendron, and calla lily.

Symptoms Depending on species or cultivar, infected plants may develop ringspots, mosaics, and leaf distortions and/or color breaks.