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Factors Affecting the Development of Cavity Spot of Carrot. E. Vivoda, Graduate Student, Department of Plant Pathology, University of California, Davis 95616. R. M. Davis, J. J. Nuņez, and J. P. Guerard. Extension Specialist, Staff Research Associate, Department of Plant Pathology, University of California, Davis 95616, and Farm Advisor, 1031 Mt. Vernon Avenue, Bakersfield, CA 93307. Plant Dis. 75:519-522. Accepted for publication 16 November 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0519.

Pythium violae and P. ultimum, isolated from cavity spot lesions on carrots produced in California, caused typical cavity spots on carrots grown in artificially infested soil in the greenhouse. In a 2-yr survey of 54 fields in the San Joaquin Valley of California, cavity spot incidence was not correlated with soil pH, electrical conductivity, moisture-holding capacity, organic matter, total and exchangeable calcium, particle size distribution, or planting densities (57, 115, or 230 carrots per meter of row). In a growth chamber maintained at 20 C, six commonly grown carrot cultivars were susceptible to both Pythium spp. Five-month-old carrots inoculated with either P. violae or P. ultimum developed about twice the number of lesions that developed on 3- or 4-mo-old carrots. Both pathogens were more virulent at 15 C than at 20 or 25 C. The number of cavity spot lesions per carrot was greater in soils continuously flooded for 24 or 48 hr than on carrots grown in nonflooded soil. P. violae was more virulent than P. ultimum in all experiments.