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Ecology and Epidemiology

Prediction of Weather-Mediated Release of Conidia of Botrytis squamosa from Onion Leaves in the Field. M. L. Lacy, Professor, Department of Botany and Plant Pathology, Michigan State University, East Lansing, MI 48824-1312; G. A. Pontius, laboratory assistant, Department of Botany and Plant Pathology, Michigan State University, East Lansing, MI 48824-1312. Phytopathology 73:670-676. Accepted for publication 23 November 1982. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-670.

Large catches of Botrytis squamosa conidia with a Burkard recording spore trap in an onion field plot were almost always preceded by a 2- to 3-day period of fairly constant moderate (12- 20 C) temperatures and low (0- 5 mb) vapor pressure deficits (E_def). The more common weather pattern yielding smaller spore catches consisted of greater fluctuations in temperatures (15- 30 C) and E_def (0- 15 mb) values. Frequent rain showers usually occurred during periods when large numbers of spores were trapped, but did not directly trigger spore release. Multiple regression analysis identified temperature and E_def as the weather variables most strongly associated with spore release. A sporulation index (based on average temperature and E_def values for the preceding 72-hr period) was devised that accurately predicted the initial large release of conidia by B. squamosa about 85% of the time. Subsequent conidial releases were predicted with somewhat lower accuracy.