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Etiology

Flower Blight and Scape Girdling of Onion Grown for Seed Production in New York. G. R. Ramsey, Research assistant, Department of Plant Pathology, New York State College of Agriculture and Life Sciences, Cornell University, Ithaca 14853; J. W. Lorbeer, professor, Department of Plant Pathology, New York State College of Agriculture and Life Sciences, Cornell University, Ithaca 14853. Phytopathology 76:599-603. Accepted for publication 11 October 1985. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/Phyto-76-599.

An epidemic of onion flower blight occurred in Orange County, New York, during the wet July of 1976. The disease occurred at low levels during the drier Julys of 1977-1981. Blighted onion umbels were categorized into four symptom types (types 1-4), from umbels with a small group of blighted florets to umbels with all the florets or seed capsules blighted. For type 1, infection occurred near the bases of pedicels from which Botrytis allii was most frequently isolated during 1980, but B. cinerea and B. byssoidea were isolated occasionally. For types 2-4, infections occurred above the base of pedicels and the symptom types were differentiated by the number, development stage, and pattern of blighted florets. From umbels of these types, B. cinerea and B. allii were isolated most frequently in 1980, with occasional B. squamosa and B. byssoidea. All four Botrytis species were isolated each year from 1976 to 1981 from florets excised from umbels with the two most commonly observed symptom types, 2 and 3, During 1976. B. squamosa was isolated from blighted florets more frequently, and B. allii less frequently, than during 1977-1981. Numbers of conidia of B. squamosa trapped in July were 16 times higher during 1976 than during 1977-1982.