Plant Disease Management Handbook

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Petunia (Petunia spp.) - Impatiens Necrotic Spot

Image related to Petunia (Petunia spp.)-Viruses

Plants infected with TMV have mottled green and yellowish green deformed leaves.

OSU Plant Clinic Image, 2014.

Plants infected with TMV can also have necrotic lesions as well as deformed leaves.

OSU Plant Clinic Image, 2014.

Plants infected with TMV may have very subtle mottling of the leaves.

OSU Plant Clinic Image, 2014.

Cause Sclerotinia sclerotiorum, a fungus that produces hard, black sclerotia, which can survive many years in soil. Sclerotia germinate to form hyphae that may attack plant stems and roots or produce apothecia that contain sexual dispersal spores in the spring. Spores may come in from nearby vegetable fields with the same disease. The disease develops in cool, wet conditions and is more prevalent when plants form a complete, compact canopy that holds high relative humidity.

Note mycelial webbing on this poor petunia plant that had stem rot and dieback.

OSU Plant Clinic image, 2010.

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Greenhouse Plants, Ornamental - Shoot Proliferation and Leafy Gall

Image related to Petunia (Petunia spp.)-Shoot Proliferation and Leafy Gall

OSU Plant Clinic Image, 2013.

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Greenhouse Plants, Ornamental - Impatiens Necrotic Spot

Symptoms Yellow, white, or brown spots are often observed with a brown border. Less frequently seen are mottle or mosaic symptoms. The cultivars Calypso, Summer Madness, and Super Blue Magic are good indicators of both tomato spotted wilt virus and impatiens necrotic spot virus.

Cause Damping-off refers to a disease that develops on the seed, radicle, hypocotyl, epicotyl, or stem of an emerged seedling. Damping-off is caused by the organisms Pythium spp., Rhizoctonia solani, and Fusarium spp. These organisms also can cause stem lesions and root rot of older plants.

Poor germination or stand development can indicate pre-emergence damping-off where seeds rot in the media prior to emergence above ground. Low germination in a petunia row between rows of seed that have germinated.

Jay W. Pscheidt, 2019.

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Greenhouse Plants, Ornamental - Gray Mold

Image related to Petunia (Petunia spp.)-Botrytis Blight

Botrytis can be seen sporulating on this Petunia flower.

Lisa Jones, 2015.

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Greenhouse Plants, Ornamental - Black Root Rot

The stunted plants are due to black root rot.

Photo by Jay W. Pscheidt, 2002.

Image related to Petunia (Petunia spp.)-Black Root Rot

Black root rot has stunted these plants.

Photo by Melodie Putnam.

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Vinca spp. (Periwinkle)

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Poinsettia (Euphorbia pulcherrima) - Pythium Root Rot

Cause Golovinomyces cichoracearum (formerly Erysiphe cichoracearum) has been reported in Washington, and Podosphaera fusca (formerly Sphaerotheca macularis) has been reported in Washington and Idaho. The classification in the rest of the world has Podosphaera pericallidis. The fungi are favored by conditions that produce high humidity but dry leaves.