Post harvest diseases fruits and vegetables - Xavier University ...

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
CHAPTER 9
CHEMICAL CONTROL
Chemical substances intended for controlling postharvest diseases
may be fungicides and bactericides (lethal to fungi and bacteria), or
fungistats and bacteristats (inhibiting fungal and bacterial development).
To serve its purpose, the chemical should come into contact with the
pathogen; the minimal effective concentration is pathogen dependent.
Chemical treatments can be applied under various strategies, with
various timings: (1) preharvest application to prevent infection in the
field; (2) sanitation procedure to reduce the level of inoculum in the
environment to which injured fruits or vegetable are liable to be
exposed; (3) postharvest application to prevent infection through wounds
and to eradicate or attenuate established infections, so as to prevent
their development and spread during storage. In order to choose the
appropriate strategy for decay control, we have to understand the mode
of infection of the pathogen, its time of infection, and the environmental
factors that may affect disease development.
A. PREHARVEST CHEMICAL TREATMENTS
The possibility of controlling well established pathogens by
postharvest disinfection is very small since most fungicides are unable to
penetrate deeply into the tissues, and effective concentrations of the
fungicide would not reach deep-seated infections. The effective way to
reduce infections initiated in the field, including quiescent infections, is
the application of broad-spectrum protective fungicides to the developing
fruit on the plant, in order to prevent spore germination or infection
establishment in the lenticels or in floral remnants of the fruit. In
practice, preharvest fungicides are combined with other preharvest
treatments applied against pests in the field.
A classic example of an effective preharvest treatment is the
preventive spraying of citrus fruit in the grove with fixed copper
compounds, to inhibit incipient infections of brown rot {Phytophthora
citrophthora) in the fruit peel. In this case, the preventive sprays are
essential for disease control, since penetration of the fungal zoospores
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