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Letter to the Editor

Threshold Criteria for Model Plant Disease Epidemics. II. Persistence and Endemicity. M. J. Jeger and F. van den Bosch. First author: Natural Resources Institute, Central Avenue, Chatham Maritime, Chatham, ME44TB, UK; and second author: Department of Phytopathology, Agricultural University of Wageningen, P.O. Box 8025, 6700EE Wageningen, the Netherlands. Phytopathology 84:28-30. Accepted for publication 15 September 1993. Crown copyright 1994. doi:10.1094/Phyto-84-28.

Onstad and Kornkven (9) defined endemicity (of a plant disease) as "the persistence or constant presence of a pathogen in an ecologically proper spatial unit over many generations." The constant presence of a pathogen was effectively taken to mean a nonzero density of infected (i.e., latent plus infectious disease), but not postinfectious, plant tissue (or plant units) over the time scale of model simulations performed with a supercomputer. This definition appears conceptually novel and potentially useful, and although the authors disavow an equilibrium approach, there are clearly long-term properties of persistence to consider.