Influence of Grower Activity on Concentrations of Airborne Conidia of Botrytis cinerea Among Geranium Cuttings. M. K. Hausbeck, Former Graduate Research Assistant, Department of Plant Pathology, The Pennsylvania State University, University Park 16802. S. P. Pennypacker, Associate Professor, Department of Plant Pathology, The Pennsylvania State University, University Park 16802. Plant Dis. 75:1236-1243. Accepted for publication 26 May 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-1236.

The relationship of grower activities to concentrations of airborne conidia of Botrytis cinerea among geranium (Pelargonium × hortorum) cuttings was studied within a commercial-propagation greenhouse. Hourly concentrations of conidia of B. cinerea were estimated for selected time periods of the 1986 and 1987 growing seasons with a Burkard recording spore trap in two propagation areas. Conidia of B. cinerea were present in the greenhouse throughout the propagation cycle. Each grower activity associated with crop production, including planting, shipping, filling benches with cuttings, cleaning benches, irrigating, fertilizing, and spraying pesticides, resulted in peak conidial concentrations (PCCs) (>50/m³/hr) in the greenhouse atmosphere. During a 7- to 12-day period between planting and application of a fungicide, newly planted cuttings were exposed to PCCs associated with grower activity in nearby established cuttings. Even though fungicides were applied, the PCCs occurring during grower activity increased as the propagation cycle progressed and cuttings matured.