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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
Physical Means 201
effective in controlling brown rot on sweet cherries, peaches and
nectarines, than unheated water treatments containing higher
concentrations (Jones and Burton, 1973).
In heat-sensitive mango cultivars, the addition of fungicides to the hot
water enabled the temperature needed for controlling anthracnose
{Colletotrichum gloeosporioides) to be reduced below the level which
causes heat injury (Spalding and Reeder, 1986b). Such a reduction
obviates the need for pedantic temperature control during treatment.
The mechanism of improved control with heated fungicide mixes may be
related in part to the direct effect of heat or to increased chemical
activity; however, improved control may also be attributed to increased
penetration of the fungicides into the host tissues (Wells and Harvey,
1970). Trials with mature guavas similarly indicated that the incidence
of rots, including Colletotrichum and Pestalotia spp., was greatly reduced
by a 5-min dip in benomyl (0.5-2.0g l-^) heated to 48-50°C, compared with
the effect of each treatment alone (Wills et al., 1982).
The fungicidal activity of imazalil, which is registered for postharvest
application to citrus fruit, to reduce both the incidence and the
sporulation of Penicillium digitatum, was considerably increased when
the fungicide was applied in hot water. Studies with Redblush
grapefruits (Schirra et al., 1995) showed that dipping the fruits for 3 min
in 1500 ppm imazalil solution at 50°C considerably increased the effect of
the chemical, compared with its use in cold water, on fruits stored for 16
weeks at 8°C followed by shelf-life conditions.
The chilling injury index under these conditions was threefold lower
than in fruits dipped in water at 20''C. Smilanick et al. (1997) found that
imazalil effectiveness on citrus fruit was substantially improved when the
fruits were passed through an aqueous solution of the chemical heated to
only 37.8°C, as compared with the current commercial practice, in some
areas, of spra5dng wax containing imazalil at ambient temperatures. The
improvement in imazalil efficacy in this case was due not only to the
combination of the fungicide with heating, but also to its application in
water, which is known to reduce the green mold more effectively than
application in wax (Eckert et al., 1994). In addition, heating the fungicide
solutions also accelerates the accumulation of fungicide residues in the
fruit (Schirra et al., 1995), and the immersion of lemon or orange fruits for
30 s in a 350-400 |ig ml-i fungicidal solution, instead of spraying the
fungicide on the fruit, deposited sufficient residues (2-4 |ig gi) to control
P. digitatum sporulation on the fruit. No rind injury was observed
following these procedures (Smilanick et al., 1997).
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