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Spore Production and Dispersal of Alternaria dauci. J. O. Strandberg, Associate Plant Pathologist, University of Florida, Agricultural Research and Education Center, Sanford, FL 32771; Phytopathology 67:1262-1266. Accepted for publication 25 April 1977. Copyright 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-1262.

In greenhouse and growth chamber studies, conidia of Alternaria dauci were produced during night hours on necrotic areas of infected carrot leaf tissue. Relative humidities of 96-100% or free moisture were required for conidiophore and conidia production. Conidia were produced over the range of 8-28 C, but were not abundant when night temperatures were below 7-8 C. In field studies, conidia were dispersed by winds above 2 to 3 m/sec when relative humidity dropped soon after daylight. Conidia were not detected during night hours. The number of hours of relative humidity above 95% during the night preceding conidial release was not correlated with the relative abundance of conidia above infected carrot fields (r = 0.13), whereas hours of continuous foliar wetness during the same period were correlated with the observed abundance of conidia (r = 0.35).

Additional keywords: Daucus carota, epidemiology.