Diseases and Management of Crops under Protected Cultivation

(Diseases and Management of Crops under Protected Cultivation)
Biocontrol of Foliar Plant Pathogens under Protected Cultivation
A.K. Tewari
Department of Plant Pathology, G.B.P.U.A&T., Pantnagar- 263 145 (UK)
The world area under protected crops is 307,000 ha, with vegetables occupying 65%
(200,000 ha) and ornamentals, 35% (107,000 ha), while in India it is approx 30,000 hectares.
Insects and diseases are the major challenges under protected cultivation as it provides
favourable environment conditions. The greenhouse environment presents a unique situation that
makes conditions more favourable for foliar diseases especially powdery mildew, downy mildew
and gray mould caused by fungi and bacterial diseases caused by Xanthomonas and
Pseudomonas. Some of the conditions that favour diseases also favours the biocontrol agents for
the management of foliar diseases. Biocontrol in greenhouses may have a greater potential
because of the development of fungicide resistance in the pathogen; workers are at greater risk of
fungicide exposure in the greenhouse as most fungicides require a re-entry period; fungicides
have a longer residual activity; controlled environment of green houses favours the survival and
growth of biocontrol agent; availability of limited number of registered fungicides; most of the
fungicides can not be used due to pre-harvest period of most of the vegetables; environmental
awareness and consumer concern due to the ill effect of the fungicides and for the production of
organic and export oriented products; reduced area and high density of planting; safe, non-toxic to
humans and animals and are rapidly biodegradable. Bio-pesticides currently represent about 1.5-
2.0 % of the world pesticide market. However, the growth rate of bio-pesticide over the next ten
years has been forecast at 10-15% annually in comparison to 2% of chemical pesticides. During
the last ten years, over 80 biocontrol products have been marketed worldwide. A large of these
has been developed for greenhouse crops. However, not all of these products are registered as
biocontrol agents, but some are also marketed as plant growth promoters, plant strengtheners, or
soil conditioners Most of these products are formulations of either of the fungi Trichoderma,
Ampelomyces or the bacteria Pseudomonas and Bacillus. Because of the high value and
emphasis on quality of greenhouse crops, a biocontrol agents should be recommended, if can
perform with the consistency and efficacy as of fungicides.
The increased use of biological controls has led to a reduction in pesticide applications and
leads to environmentally responsible, intensive crop production. The primary strategy of biological
control for greenhouse plant diseases is to introduce fungal parasites to control disease causing
fungi in the greenhouse environment so that pathogens are unable, or have a reduced ability to
infect the plants. Research in developing biological controls for greenhouse crop diseases is
ongoing and it is likely that more potential products of the biological control will be available in the
near future for greenhouse diseases. Biocontrol agents should be used as preventative measures
and/or in combination or alternating with compatible fungicides for the effective management of
foliar diseases.
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