Plant Disease Management Handbook

Cause Sclerotinia sclerotiorum, a fungus that produces hard, black sclerotia, which can survive many years in soil. Sclerotia germinate best when soil temperature is 55°F to 60°F. The fungus can colonize dead organic plant matter and survive many years. As a rule, these plants tend to be susceptible to overwatering. In the potato system, flowers are very susceptible to infection and are the main source of stem infection.

Cause Golovinomyces cichoracearum (formerly Erysiphe cichoracearum) has been reported from Idaho and it is a common garden problem in Oregon. The fungus is favored by conditions that produce high humidity but dry leaves. They are highly specialized pathogens that form a close association with the host. Conditions that favor the host also favor the pathogen.

Image related to Rudbeckia spp. (Black-eyed Susan)-Powdery Mildew

Powdery mildew can cover leaves late in the growing season.

Jay W. Pscheidt, 2014.

Powdery mildew may cover much of the plant late in the season.

Jay W. Pscheidt, 2014.

Cause Several fungi can cause leaf spots. Ramularia rudbeckiae has been reported from Idaho, and Septoria rudbeckiae has been reported from Idaho and Washington. Generally, weather or irrigation that keeps leaves wet for extended periods favors these diseases.

Cause Several root rotting organisms have been detected in rosemary root rot samples coming to the OSU Plant Clinic. Pythium, Berkeleyomyces sp. (formerly Thielaviopsis basicola), and Rhizoctonia are among the organisms found. Rosemary is native to seaside cliffs and thus over watering and too much fertility inhibit good growth. These same soil conditions favor many root-rot organisms.

Image related to Rosemary (Rosmarinus officinalis)-Root Rot

Black root rot on rosemary.

OSU Plant Clinic Image, 2014.

Pythium root rot of rosemary.

OSU Plant Clinic Image, 2011.

See:

Greenhouse Plants, Ornamental - Gray Mold

Image related to Rosemary (Rosmarinus officinalis)-Botrytis Stem Canker

Stem lesions due to Botrytis sp.

OSU Plant Clinic Image, 2012.

Gray sporulation of Botrytis sp.

OSU Plant Clinic Image, 2011.

Defoliation and dieback of stems where portions above cankers wilt, die, and collapse when girdled.

OSU Plant Clinic Image, 2011.

See:

Rose (Rosa spp.) and hybrids - Bacterial Leaf Spot and Blast

Winter injury of rose. Note the black and yellowed canes.

Photo by Jay W. Pscheidt, 1991.

See:

Rose (Rosa spp.) and hybrids - Rose Mosaic

Rose (Rosa spp.) and hybrids - Chemical Injury

Image related to Rose (Rosa spp.) and hybrids-Virus Diseases

This disease is known as Rose Mosaic but is actually due to several viruses.

Photo by Melodie Putnam, 1998.

Abnormally thorny stems for this 'Knockout' rose lead to a Rose rosette diagnosis.

OSU Plant Clinic Image, 2018.

Cause Verticillium dahliae, a fungus that lives a long time in soil and can infect a wide range of hosts. Rootstocks such as Rosa odorata and 'Ragged Robin' are susceptible; R. multiflora and 'Dr. Huey' have more resistance. R. chinensis var. manetti is very resistant. Under favorable growing conditions plants may be able to tolerate infection.