Plant Disease Management Handbook

Cause The fungus Sclerotinia sclerotiorum has an extremely wide host range infecting 383 plant species in at least 64 families. The disease develops in cool, wet conditions and is more prevalent when plants form a complete, compact canopy that holds high relative humidity. Individual sclerotia (survival structure of the fungus) can survive 3 years, but the fungus can colonize dead organic plant matter and survive many years.

Cause Fusarium oxysporum f. sp. delphinii has been reported on delphinium from Washington. The fungus usually infects the roots or stems through wounds. Macroconidia and microconidia are formed in sporodochia on stems and can be disseminated by windblown and/or splashed rain. Warm temperatures, wet conditions favor disease severity, and pH has little effect.

See:

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

Cause Several fungi such as Erysiphe spp. and Podosphaera spp. can cause powdery mildew but only Erysiphe polygoni and Golovinomyces cichoracearum (formerly Erysiphe cichoracearum) have been reported from the PNW. Conidia are released in response to abrupt decreases in relative humidity.

Cause The fungus Calophoma aquilegiicola (formerly Diplodina delphinii) has been found by the OSU Plant Clinic. The fungus overwinters on host debris and in the crown of living plants. The disease is favored by warm wet weather, high humidity, and excessive fertilization. Injury is not needed for the fungus to gain entry into various plant parts.

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

See:

Greenhouse Plants, Ornamental - Gray Mold

Cause The bacterium Pseudomonas syringae pv. delphinii has been found on Delphinium by the OSU Plant Clinic. Another bacterium, Pseudomonas chicorii, has similar symptoms but has not been reported from the Pacific Northwest. These bacteria survive as soil inhabitants, in plant debris and in the crowns of infected plants. Contaminated soil particles can be moved by water, tools, and people.

Cause The fungus Puccinia hemerocallidis is an exotic rust native to Asia. This pathogen was detected in daylily (Hemerocallis spp.) nursery stock in the southeast in 2000. It has since spread to many other states and was detected at one site in Benton Co., Oregon in 2001. The infected plants were imported from a nursery in Florida. An eradication program was implemented at that site and none was found in 2002.

See:

Greenhouse Plants, Ornamental - Gray Mold

Cause Botrytis cinerea, a fungus. The disease is favored by warm and moist conditions. Can survive in dead plant debris and is ubiquitous in most Pacific Northwest production areas.