First Report of Downy Mildew on Delphinium Caused by Peronospora ficariae in California

Plant Disease
S A Tjosvold, S T Koike

Abstract

Along California's central coast, delphinium (Delphinium species and cultivars) is grown as a cut flower and potted plant. In the spring of 2003, severe downy mildew was observed on various delphinium crops in Santa Cruz County. The disease was detected on cut flower Delphinium 'Volkerfrieden' in a greenhouse and adjacent field production areas. At a different nursery, outdoor, containerized D. grandiflorum 'Blue Butterfly' and Delphinium elatum (Pacific Hybrids) were also infected. Initial symptoms on leaves consisted of light green patches. These areas quickly turned dark green to blackish green and often were delimited by the central vein of the leaf. Purple-gray sporulation of the pathogen could be seen primarily on the abaxial leaf surfaces. Symptoms were most severe on older foliage. As disease progressed, the lower leaves withered and dried up, giving the plant a blighted appearance. Disease was most severe on D. grandiflorum 'Blue Butterfly', in which the disease affected the entire planting and blighted all foliage with the exception of the youngest leaves on the plant's central leader. For this cultivar, the diseased nursery stock had to be discarded, resulting in significant economic loss. Sporangiophores branched di...Continue Reading

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