Plant Disease Management Handbook

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Greenhouse Plants, Ornamental - Impatiens Necrotic Spot

Image related to Impatiens-Impatiens Necrotic Spot

Spots can be seen on some of these leaves of 'Rosebud' impatiens.

OSU Extension Plant Pathology Slide Set, 1990.

Multiple necrotic spotting may be seen rather than a single spot which could easily be confused with fungal infection.

OSU Plant Clinic Image, 2014.

Cause Plasmopara destructor is a host-specific, fungus-like organism known as an oomycete, or water mold. There have been sporadic reports in greenhouses since 2004, but it was not until summer 2011 that regional outbreaks of this disease were seen for the first time in landscape beds and container plantings in North America. The disease was found in landscapes in Oregon and Washington since 2012. Impatiens business dropped 50% to 60% due to this disease alone.

Image related to Impatiens (Impatiens walleriana)-Downy Mildew

Leaf yellowing, stippling and down curling may be seen with or without the white moldy growth under leaves.

Robin Rosetta, 2012.

Look for white fungal moldy growth on the underside of leaves.

Robin Rosetta, 2012.

Leaf yellowing and stippling may be seen with or without the white moldy growth under leaves.

Robin Rosetta, 2012.

Defoliation is common in advanced infections where plants look like flowers on green sticks.

Luisa Santamaria, 2012.

Plants infected early are stunted.

Robin Rosetta, 2012.

Only Impatiens walleriana are infected with this downy mildew. The disease has been found in landscapes as well as production greenhouses.

Robin Rosetta, 2012.

Defoliated stems and collapsing plants are found in the later stages of this disease.

Robin Rosetta, 2012.

See:

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

Plants have collapsed due to Rhizoctonia sp.

Photo by Stacy Fisher, 1990.

See:

Greenhouse Plants, Ornamental - Gray Mold

Image related to Impatiens-Botrytis Blight

Flowers are often attacked by Botrytis especially as they become senescent.

Jay W. Pscheidt, 2002.

Botrytis colonized flowers may fall onto leaves allowing the fungus to gain entry into these tissues.

Jay W. Pscheidt, 2002.

See:

Hazelnut (Corylus avellana) - Bud Rot (Anthracnose)

Hazelnut Cultivar Susceptibility

Trees seem to die randomly in the orchard during the summer.

Jay W. Pscheidt, 2010.

Exposed, discolored cambium originating from the top of the tree.

Photo by Jay W. Pscheidt, 1991.

Image related to Hazelnut (Corylus avellana)-Bacterial Blight

Notice the discolored cambium exposed in this picture of bacterial blight on an older tree. The canker does not go below soil line.

Photo by Jay W. Pscheidt, 1989.

Leaf spot due to bacterial blight.

OSU Plant Clinic Collection, 2011.

Branch and bud dieback due to bacterial blight.

Larry Moore collection, 1970.

Leaf spots due to bacterial blight.

Larry Moore collection, 1969.

Cause Rust on the common garden ground cover (creeping St. John's Wort - H. calycinum) is caused by the fungus Melampsora hypericorum. The same rust can occur on the therapeutic herb H. perforatum. Another rust, Uromyces hypericifrondosi (formerly Uromyces triquetrus) (which may also be called U.

Yellow, red, or brown spots scattered on many of the leaves.

Jay W. Pscheidt, 2008.

Powdery orange spots on the underside of leaves.

Jay W. Pscheidt, 2008.

Diffuse orangish spots on the top side of leaves with powdery orange spots on the underside of leaves.

Jay W. Pscheidt, 2008.

Yellowish spots on the underside of a Hypericum leaf.

Jay W. Pscheidt, 2008.

Image related to Hypericum (St. Johnswort)-Rust

Infected plants make the bed look sparse and unattractive.

OSU Extension Plant Pathology Slide Set.

See:

Greenhouse Plants, Ornamental - Impatiens Necrotic Spot

Cause There are 14 viruses reported for hydrangea. Hydrangea ringspot virus (HRSV) can be transmitted mechanically by leaf contact or by knives but not through seed or by aphids. Suspected as cause of hydrangea running-out. Many cultivars are tolerant of the virus.

Not a great picture but you can see the reddish spots on the leaves from Hydrangea ringspot virus.

OSU Extension Plant Pathology Slide Set, 1984.

Leaf spots from these viruses look similar. Tomato spotted wilt on the left and Hydrangea ringspot on the right.

OSU Extension Plant Pathology Slide Set.

Cause Erysiphe friesii var. friesii (formerly Microsphaera friesii) has been reported from Washington and Erysiphe polygoni has been reported from British Columbia. These fungi are favored by conditions that produce high humidity but dry leaves such as heavily-shaded growing sites. It is a highly specialized pathogen that forms a close association with the host.