Plant Disease Management Handbook

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Greenhouse Plants, Ornamental - Shoot Proliferation and Leafy Gall

Multiple buds (areal gall) due to the bacteria Rhodococcus fascians.

OSU Plant Clinic image, 2010.

Cause Puccinia pelargonii-zonalis, an autoecious (can complete their life cycle on this one host) rust fungus that survives on living plants and plant debris. Movement of infected cuttings can also spread this fungus. Infections occur readily if leaves are wet 5 to 6 hours at 55°F to 75°F. Urediniospores may be infective at least 3 months. Considerable genetic variation exists from highly susceptible to immune cultivars.

Image related to Geranium (Pelargonium spp.)-Rust

Diffuse, circular, pale-green to yellow spots appear on the upper leaf surface while dark, brown uredia form on the underside.

Photo by Ralph S. Byther

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Cabbage and Cauliflower (Brassica oleracea) - Oedema (Edema)

Image related to Geranium (Pelargonium spp.)-Oedema

Whole plant symptoms of oedema on this Ivy Geranium 'Red Blizzard'.

Melodie Putnam, 2006.

Note all the tan to brown areas on these leaves.

Photo by Ralph S. Byther

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Greenhouse Plants, Ornamental - Impatiens Necrotic Spot

Poor picture trying to depict ringspot symptoms on leaves. Slide labeled Tomato Spotted Wilt.

Photo by Jay W. Pscheidt, 1993.

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Greenhouse Plants, Ornamental - Gray Mold

Mature flowers are more likely to show symptoms than immature flowers.

Jay W. Pscheidt, 2020.

Image related to Geranium (Pelargonium spp.)-Botrytis Blight

Note the gray, fuzzy growth of the fungus along this petiole. The fuzzy growths along the healthy petioles are trichomes.

Photo by Walter F. Mahaffee, 1997

Spent flowers colonized by Botrytis can be a source of infection for leaves.

Jay W. Pscheidt, 2018.

Under the right moist conditions, the gray sporulation of Botrytis can be observed.

Jay W. Pscheidt, 2020.

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Greenhouse Plants, Ornamental - Black Root Rot

Image related to Geranium (Pelargonium spp.)-Black Root Rot

Black rotted roots of this 'Rozanne' geranium.

OSU Plant Clinic Image, 2014.

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Greenhouse Plants, Ornamental - Pythium Seed Rot, Damping-off, and Root Rot

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Poinsettia (Euphorbia pulcherrima) - Bacterial Leaf Spot

Round spots are dark green to black and slightly sunken.

Melodie Putnam, 2001

Image related to Geranium (Pelargonium spp.)-Bacterial Blight

Atypical symptoms; note the wedge-shaped damage on leaves.

Photo by Jay W. Pscheidt, 1992.

Angular, dead areas occur when sectors of leaves bounded by the veins die.

Photo by Melodie Putnam, 2001

Cause This fungal disease, caused by Alternaria alternata, has not been formally reported from the Pacific Northwest but has been found on a few samples sent to the OSU Plant Clinic. The disease is favored by prolonged cool, moist conditions and low nitrogen fertility. Older leaves are particularly susceptible if they are senescing. The fungus survives on dead leaves on the soil surface and spores are spread by air currents.

Image related to Geranium (Pelargonium spp.)-Alternaria Leaf Spot

Note the necrotic spots on this leaf.

Photo by Melodie Putnam, 2000.

Cause Sclerotium cepivorum (teleomorph: Stromatinia cepivora), a fungus. Enough sclerotia from an initially high population may survive 20 to 30 years or more in soil without the presence of an Allium host to incite unacceptable levels of disease in the next Allium crop. Only Allium spp. such as onion, leek, and shallot are attacked.

Image related to Garlic (Allium sativum)-White Rot

Garlic bulb with white rot.

Photo by Steve Renquist, OSU Extension, 2010