Plant Disease Management Handbook

Cause A fungus, Fusarium oxysporum f. sp. gladioli, that lives in soil and plant debris for many years as chlamydospores. Population levels are highest in the top 8 inches of soil. Spores infect roots and cross the basal plate. These infections may continue to enter and spread within the vascular tissues. The fungus is spread widely by contaminated soil and infected corms while local spread can be by water flow and rain splash.

Image related to Iris, Bulbous (Iris spp.)-Fusarium Basal Rot

These plants have multiple problems including Fusarium root rot.

OSU Plant Clinic collection, 2012.

Cause Sclerotium delphinii, a fungus. The sclerotia overwinter in soil or affected plant parts. Infection usually occurs on the stems near the soil surface. Disease development and spread can occur very rapidly under mild to warm, moist conditions in the field or in storage after digging. The disease is widespread and can be serious. In the Pacific Northwest, crown rot is more common on bulbous iris, tulips and lilies than daffodils.

Image related to Iris, Bulbous and Rhizomatous (Iris spp.)-Crown Rot

Young cotton ball-like sclerotia of Sclerotium sp. can been seen forming within the white mycelium.

Maryna Serdani, 2012.

Leaves have died back from infection by a Sclerotium sp.

Maryna Serdani, 2012.

See:

Garlic (Allium sativum) - Blue Mold Rot

Tulip - Penicillium Bulb Rot (Blue Mold)

Go to:

Cedar, Incense

See:

Photinia - Leaf Spot

Spots will be on plants throughout the year until the leaves are shed.

Jay W. Pscheidt, 2008.

See:

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.

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.