Co-Authors:
Elad, Y., Department of Plant Pathology, ARO, Volcani Center, Bet Dagan 50250, Israel
Abstract:
Traditionally, foliar diseases of greenhouse-grown crops have been classified into two groups: (i.) diseases that develop during the wet and cold winter, under conditions of free moisture and high relative humidity and (ii.) diseases of dry conditions that develop from spring to autumn. Common diseases in group i are gray, leaf and white molds, late blight, rusts and downy mildews; those of group ii. Include powdery mildews. The pattern of occurrence and the severity of epidemics of foliar diseases of greenhouse crops has changed in recent years. This is attributed to the spread of greenhouse cultivation, improvement of climate management and the extension of greenhouse cropping throughout the year, together with the introduction of new cultivars and agrotechniques. Israeli and Mediterranean greenhouses have tended to become drier and warmer during winter while the use of greenhouses with moderate temperatures during the summer has become more popular than in the past. As a consequence, changes have taken place in the significance of certain diseases and their severity, as the duration of periods with microclimate suitable for epidemics has been extended and diseases develop during previously disease free seasons. Examples of the change in the prevalence of humidity-promoted diseases are the increased severity and earlier appearance of tomato downy mildew during autumn, frequent epidemics of rust and downy mildew during summer in greenhouse-grown roses, and the increased severity of tomato leaf mold during most of the year, including the summer. Conversely, powdery mildew epidemics are increasingly frequent in greenhouses, especially warmed ones, during winter; the most pronounced of these is the outbreak of pepper powdery mildew. These phenomena call for adoption of suitable disease management techniques.
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