A New Canker and Twig Dieback Disease of Apple and Crabapple Trees Caused by Sphaeropsis pyriputrescens in Washington State

Plant Disease
C L Xiao, R J Boal

Abstract

Crabapple (Malus sylvestris) is commonly used as a source of pollen in apple production. During September and October 2003, a canker and twig dieback disease of 'Manchurian' crabapple trees was observed in some commercial apple (Malus × domestica Borkh.) orchards (7- to 10-years-old) in north-central Washington State. A fungus was consistently isolated from 40 to 77% of sampled crabapple trees. During May 2004, the same symptoms and fungal association were observed in an 8-year-old 'Fuji' apple orchard in which all crabapple pollenizers and 43% of the Fuji trees were diseased. Canker and dieback appeared to originate from infection of dying or dead fruit spurs or pruning wounds. Cankered areas were slightly sunken, brown and the margin of diseased area often developed cracks in the cortical tissue. Pycnidia were often present in older areas of the lesion. Pycnidia were black, 0.3 to 0.6 mm in diameter, separate to aggregated in small numbers, and partially immersed to nearly superficial in the diseased tissue. To isolate the fungus, outer bark tissues of diseased twigs were scraped and small tissue segments were cut from the canker margin. Tissue segments were surface disinfested for 5 min in 0.5% sodium hypochlorite solution, ...Continue Reading

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