Diseases and Management of Crops under Protected Cultivation

(Diseases and Management of Crops under Protected Cultivation)
Importance of Protected Crops for Plant Production
Greenhouses were initially built in areas with long, cold seasons to produce out-of season
vegetables, flowers and ornamental plants. Northern Europe is the paradigm of pioneering areas
of greenhouse cultivation. Greenhouses protect crops against cold, rain, hail and wind, providing
plants with improved environmental conditions compared to the open field. In greenhouses, crops
can be produced out-of-season year-round with yields and qualities higher than those produced in
the open field. Greenhouses have also allowed the introduction of new crops, normally foreign to
the region (Germing, 1985).
There are two basic types of greenhouse. The first type seeks maximum control in an
environment to optimize productivity. In Europe, optimal conditions for year-round production are
provided in the glasshouses of The Netherlands, Belgium, the UK and Scandinavia. The other type
of greenhouse, which is very common throughout the Mediterranean area, provides minimal
climatic control, enabling the plants grown inside to adapt to suboptimal conditions, survive and
produce an economic yield (Enoch, 1986; Tognoni and Serra, 1989; Castilla, 1994).
Reuveni et al,. (1989) observed a reduction in the number of infection sites of B. cinerea
on tomato and cucumber when a UV-absorbing material was added to polyethylene film to
increase the ratio of blue light to transmitted UV light. Blue photo selective polyethylene sheets
have been suggested for their ability to reduce grey mould on tomato (Reuveni and Raviv, 1992)
and downy mildew on cucumber (Reuveni and Raviv, 1997). Green-pigmented polyethylene
reduced the conidial load and grey mould in commercial tomato and cucumber greenhouses by
35–75%. Sclerotinia sclerotiorum on cucumber, Fulvia fulva (Cooke) Cif. (= Cladosporium fulvum
Cooke) on tomato and cucumber powdery mildew were also reduced (Elad, 1997).
The influence of greenhouse structures and covers on greenhouse climatic regimes may
have strong consequences for pests and their natural enemies, as they have for diseases. In hightech
greenhouses, regulation of temperature and water pressure deficit enables the creation of
conditions less favorable to pathogens and, in some cases, more favorable to bio control agents.
The use of heating to limit development of a number of pathogens is well known (Jarvis, 1992).
The use of high root temperatures in winter grown tomatoes in rock wool offers a non-chemical
method of controlling root rot caused by Phytophthora cryptogea Pethybr. & Lafferty. The high
temperature was shown to enhance root growth while simultaneously suppressing inoculum
potential and infection, and, consequently, reducing or preventing aerial symptoms (Kennedy and
Pegg, 1990). Careful control of the temperature also proved important in the case of
hydroponically grown spinach and lettuce, in which it prevented or reduced attack by both Pythium
dissotocum Drechs. and Pythium aphanidermatum (Edson) Fitzp. (Bates and Stanghellini, 1984).
Recently, attacks of P. aphanidermatum on nutrient film technique (NFT) grown lettuce in Italy
were related to the high temperature (>29°C) of the nutrient solution. Root rot was inhibited by
reducing the temperature below 24°C (Carrai, 1993).Productivity is manifold in greenhouses in
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