New Delphinium Disease

In California’s central coast, Delphinium species are grown in the field or greenhouse as a cutflower or in the field as a cutflower or potted plant. In the spring of 2003, severe downy mildew was observed on three cultivars at two production nurseries in Santa Cruz County. One nursery was a cutflower producer where symptomatic Delphinium ‘Volkerfrieden’ were found in adjacent greenhouse and field production areas. The other nursery produced field grown containerized ornamentals where symptomatic Delphinium grandiflorum ‘Blue butterfly’ and Delphinium ‘Pacific Giant hybrid’ were found. Initial symptoms on leaves consisted of light green patches. These areas quickly turned dark green to black green and often were delimited by the central vein of the leaf. Purple-gray sporulation of the pathogen could be seen primarily on the bottom of the leaf. Symptoms were most severe on older foliage. As disease progressed, the lower leaves withered and dried up. Disease was most severe on Delphinium grandiforum ‘Blue butterfly’, where the disease affected all production plants and nearly blighted the entire plant except the central leader. The pathogen was identified as Peronospora ficariae. It has been found in other parts of the world and in the United States (Alabama, Idaho, Maine, Michigan, New York, Oregon, Wisconsin, and Wyoming). It has been found on other hosts including many species of Ranunculus, Anemone coronaria, and Helleborus purpurascens.