Diseases and Management of Crops under Protected Cultivation

(Diseases and Management of Crops under Protected Cultivation)
Factors Favorable to Pest and Disease Development: Well-grown and productive crops are
generally less susceptible to diseases, but in many cases compromises have to be made between
optimum conditions for economic productivity and conditions for disease and pest prevention.
Well-fertilized and irrigated crops are, however, often more sensitive to pests, like aphids,
whiteflies and leafminers. High host plant densities and the resulting microclimate are favorable to
disease spread. Air exchange with the outside is restricted, so water vapour transpired by the
plants and evaporated from warm soil tends to accumulate, creating a low vapour pressure deficit
(high humidity). Therefore, the environment is generally warm, humid and wind-free inside the
greenhouse. Such an environment promotes the fast growth of most crops, but it is also ideal for
the development of bacterial and fungal diseases (Baker and Linderman, 1979; Fletcher, 1984;
Jarvis, 1992), of insects vectoring viruses and of herbivorous insects. For bacteria and many fungi
(causal agents of rusts, downy mildews, anthracnose, grey mould, etc.) Greenhouses are
designed to protect crops from many adverse conditions, but most pathogens and several pests
are impossible to exclude. Windblown spores and aerosols containing bacteria enter doorways
and ventilators; soilborne pathogens enter in windblown dust, and adhere to footwear and
machinery. Aquatic fungi can be present in irrigation water; insects that enter the greenhouse can
transmit viruses and can carry bacteria and fungi as well. Once inside a greenhouse, pathogens
and pests are difficult to eradicate.
Problems in protected cultivation
Greenhouses are designed to protect crops from many adverse conditions, but most
pathogens and several pests are impossible to exclude as:
1. Windblown spores and aerosols containing bacteria enter doorways and ventilators
2. Soil-borne pathogens enter in windblown dust, and adhere to footwear and machinery
3. Aquatic fungi can be present in irrigation water
4. Insects that enter the greenhouse can transmit viruses and can carry bacteria and fungi as
well
5. Once inside a greenhouse, pathogens and pests are difficult to eradicate eg. leach
Factors Stimulating Sustainable Forms of Crop Protection in Protected Cultivation:
Protected cultivation is an extremely high-input procedure to obtain food and other agricultural
products per unit of land, although inputs are the lowest when related to the yield per area.
Among the factors stimulating sustainable forms of crop protection are the following:
1. Consumer concern about chemical residues.
2. Pesticide-resistance in pests and pathogens.
3. Side-effects of chemical application are increasingly observed in old and new growing
areas.
4. Efficacy: Some pests and diseases are difficult – sometimes impossible – to control if an
integrated approach is not adopted.
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