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Disease Note

Powdery Mildew of Carrot in New York. H. R. Dillard, Department of Plant Pathology, New York State Agricultural Experiment Station, Cornell University, Geneva 14456. A. C. Cobb, and N. G. Call. Department of Plant Pathology, New York State Agricultural Experiment Station, Cornell University, Geneva 14456, and NGC Consulting, 7885 Lewiston Road, Batavia, NY 14020. Plant Dis. 76:972. Accepted for publication 4 May 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0972C.

Powdery mildew was observed on leaves and petioles of processing carrots (Daucus carota L. subsp. sativus (Hoffm.) Arcang. 'Oranza') grown in Lyndonville, New York, in September 1991. The disease was present in a single large area encompassing approximately one third of a 16-ha field. Powdery mildew was most severe on the older leaves, which were covered with white mycelia and conidia of the fungus and senesced prematurely. Conidia were produced singly a~d were 32-44 × 11-14 µm. Cleistothecia were not found, and fibroslll bodies were not observed in the conidia. The fungus was identified as Erysiphe heraclei DC. Infected leaves were gently shaken to dislodge the conidia over healthy Oranza plants grown in the greenhouse, and mildew colonies developed within 7 days. Weather conditions were conducive for development of powdery mildew during the 1991 growing season, with mean maximum temperatures of 26, 28, and 27 C and rainfall of 3.6, 3.4, and 5 cm during June, July, and August, respectively. Control of the disease with fungicides was not attempted because ofthe proximity of harvest. Yield in the affected field was not noticeably reduced. In the United States, powdery mildew of carrot was previously reported in California (1) and North Carolina (2). This appears to be the first report of powdery mildew of carrot in New York State.

References: (1) K. Abercrombie and H. C. Finch. Plant Dis. Rep. 60:780, 1976. (2) S. F. Jenkins et al. Plant Dis. 70:892, 1986.