Greenhouse environment and epidemiology of grey mould of container-grown Douglas-fir seedlings

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Abstract
The environmental parameters associated with grey mould, Botrytiscinerea Fr.: Nocca & Balbis, on container-grown Douglas-fir, Pseudotsugamenziesii (Mirb.) Franco, were studied in a plastic-covered greenhouse and a fibreglass-covered greenhouse near Victoria, British Columbia. Disease losses and numbers of B. cinerea spores were much higher in the fibreglass-covered house, where seedlings were taller and more succulent because the fibreglass reduced light intensities. From July to October the length of time when the combination of temperature and relative humidity that favours B. cinerea spore germination and infection was 14.5 times greater in the fibreglass-covered than in the plastic-covered house. Conditions beneath the seedling canopy that enhance the disease were more prevalent in July and August than in the autumn when the disease becomes evident, suggesting that earlier application of preventive fungicides may benefit disease control. Grey mould inoculum originated from outside the greenhouses, but once the disease was established on the seedlings, numbers of spores within the houses exceeded those outside. Airborne spore numbers both outside and within the greenhouses were highest during the day. Numbers of spores within the houses peaked when the irrigation system was on; this is ascribed to the mechanical effect of the irrigation water on spore dispersal rather than to changes in greenhouse environmental parameters.

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