VIEW ARTICLE

Ecology and Epidemiology

Influence of Interrupted Wet Periods, Relative Humidity, and Temperature on Infection of Carrots by Cercospora carotae. O. Carisse, Research assistant, Department of Plant Science, Macdonald Campus of McGill University, 21111 Lakeshore Road, Ste-Anne-de-Bellevue, Quebec, Canada H9X 1C0; A. C. Kushalappa, Associate professor, Department of Plant Science, Macdonald Campus of McGill University, 21111 Lakeshore Road, Ste-Anne-de-Bellevue, Quebec, Canada H9X 1C0. Phytopathology 82:602-606. Accepted for publication 29 January 1992. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1992. DOI: 10.1094/Phyto-82-602.

Carrot leaves were inoculated with a conidial suspension (10⁴ conidia per milliliter) of Cercospora carotae. Then they were subjected to interrupted and continuous wet periods of various durations and to several combinations of relative humidity (RH, 84–100%) and temperature (16–32 C) with and without an initial wet period of 6 h. Number of lesions per leaf decreased with increasing length of dry period for dry periods greater than 3 h. However, a dry period of 3 h with initial and final wet periods of 24 and 12 h, respectively, resulted in more lesions per plant than the corresponding continuous wet period (39 h). The number of lesions increased with an increase in initial wet period duration for a fixed dry interruption period of 6 h. For all temperatures, very few lesions developed at 84% RH. However, the number of lesions increased rapidly with increase in percent RH greater than 84%. In general, the plants exposed to an initial wet period of 6 h developed more lesions than those exposed to RH only. The number of lesions per plant was transformed to proportion of those at a continuous wet period and to proportion of maximum number of lesions for experiments on interrupted wet period and RH, respectively. Polynomial models were used to describe the effects of dry period durations, initial wet period durations, and combinations of RH and temperature on infection.