GLASSHOUSE CROP PEST MANAGEMENT (PLANT PATHOGENS)

Abstract

Glasshouses or greenhouses are structures covered with a transparent material for the purpose of admitting natural light for plant growth. These structures usually have automatic control over heating, cooling, ventilation, shading, air movement, and humidity. Glasshouses are used to grow a variety of vegetables, ornamentals, bedding plants, cut flowers, tree seedlings, herbs, and other plant material from tissue culture sources. In colder climates, glasshouses provide a significant amount of fresh vegetables during the time when outdoor production is not possible. The total world area under glasshouses is estimated to be 306,500 ha (1). There has been a revolution in the glasshouse production technology during the past couple of decades. Precise control of environmental conditions and nutritional status of plants has provided increased yields and powerful disease management tools (2). For optimal plant growth in a glasshouse, plants require an optimal level and quality of light, conducive day and night temperatures, relative humidity adjusted for adequate transpiration, carbon dioxide level higher than ambient air, all the essential nutrients, and adequate supply of high quality water (3, 4). Unfortunately, however, the environmental conditions provided for optimal plant growth in a glasshouse also generally are very favorable for development of many plant diseases. Any one of many stresses, including low or high temperature, overor under-watering, low or high light intensity, too little nutrients, or too high salinity could predispose a plant to a disease (5). Furthermore, dense plant communities and generally inadequate systems of air circulation and removal of moist warm air from a glasshouse create a microclimate conducive for development of foliar diseases for example gray mold (Botrytis cinerea) and white mold (Sclerotinia sclerotiorum) of cucumber. Intensive plant handling activities by workers also spread the pathogens and promote the development of epidemics. Hydroponic cultures provide an excellent system for excluding soilborne diseases. The system, however, also provides a conducive medium for large-scale multiplication and a rapid plant to plant spread of many devastating pathogens like Pythium spp. causing damping off of many greenhouse-grown plant species. Greenhouses: Advanced Technology for Protected Agriculture (6) and Managing Diseases in Greenhouse Crops (7) are two excellent books on this subject.