Plant Disease Management Handbook

See:

Calla Lily (Zantedeschia spp.) - Soft Rot

Yellowing or browning of leaves, especially the fan's outer leaves, is an early symptom. (Leaf spots are due to leaf spot fungus).

Larry Moore collection, 1971.

Decay can also occur on the floral stems.

Larry Moore collection, 1974.

See:

Potato (Solanum tuberosum) - Nematode, Potato Rot

Cause A nematode, Ditylenchus destructor, that lives in soil and can be carried in bulbs. It is rare and only in isolated regions.

Cause Mycosphaerella macrospora (asexual: Heterosporium gracile), a fungus formerly known as Didymellina macrospora. This is considered the most important foliar disease of iris and can significantly reduce bulb yields. It overwinters on dead leaves and other plant remains. Spores are produced in spring, dispersed by wind and rain and infect leaves directly or through stomata. Several disease cycles can occur in warm, wet weather.

The chlorotic halo around each spot is easy to see when light comes from behind the leaf.

Photo by Jay W. Pscheidt, 2006.

Toward the end of the season, after bloom, spots may become very numerous and run together.

Jay W. Pscheidt, 2006.

Image related to Iris, Bulbous and Rhizomatous (Iris spp.)-Leaf Spot

Notice the brown spot with a yellow margin.

Photo by Jay W. Pscheidt, 1990

Note the necrotic spot on the leaf below the flower.

Photo by Jay W. Pscheidt, 1999.

Spots can be numerous on leaves.

Melodie Putnam, 1997.

See:

Iris, Bulbous and Rhizomatous (Iris spp.) - Leaf Spot

See:

Tulip - Gray Bulb Rot

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.