Avocado - Crop Post-Harvest: Science and Technology - page 168

by insects, rodents or mechanically, allow the entrance of
the pest, which produces spores on the attacked tissue.
Among all the cultivars grown in Mexico, 'Fuerte' is the
most susceptible to this disease. 'Hass' can also be
severely affected if the pest is not prevented. 'Booth 1',
'Pollock', and 'Waldin' are considered slightly suscepti-
ble. The Mexican local hybrids (Criollos) are also likely
to be affected by the fungus, although the incidence is
lower because fruit from these trees ripens in the spring
(Gallegos 1983).

compared with higher temperatures (Hopkirk et al . 1994).
Post-harvest fungicides (prochloraz, benlate/benomyl and
thiabendazole) are used in some countries, but these are not
registered for use in the United States (Darvas et al . 1990).
Control methods include good orchard sanitation,
effective pre-harvest fungicide application, careful
handling to minimize physical injuries, prompt cooling to
optimum temperature for the cultivar and maintaining that
temperature during marketing. Pre-harvest sprays with
copper have been shown to significantly reduce post-
harvest diseases (Hartill et al . 1990a). Four sprays during
the season were insufficient to reduce post-harvest rots,
and 12 sprays were required before significant differences
were obtained. Pre-harvest Benlate application has been
shown to reduce disease significantly when three sprays
were applied during the season (Hartill et al . 1990b).
Post-harvest dipping with Sportak R appears to be
unreliable. It appears that there may be a curing effect, or
alternatively an infection period immediately after harvest
that is not halted by a delayed application of prochloraz.
Hartill et al . (1986) found no difference in rots if prochlo-
raz was applied within 24 hours of picking. Everett and
Korsten (1996) have demonstrated the effectiveness of
applying prochloraz either in wax or as an ultra low-
volume spray. Wax by itself also seemed to reduce levels
of stem end rots, however waxing has been reported to
increase the incidence of all post-harvest diseases on
'Fuerte' avocados (Darvas et al . 1990). Waxing proba-
bly increases the humidity next to the skin of the fruit,
and also the production of ethylene, both can promote
the growth of anthracnose fungi (Darvas et al . 1990;
Flaishman et al . 1995). However, Darvas et al . (1990)
have shown that wax extended the shelf life of 'Fuerte'
avocados. Fruit treated with prochloraz cannot be exported
to Asia, the United States and some countries in Europe.
Post-harvest temperature control is effective in
reducing the incidence of diseases (Truter & Eksteen
1987; Young & Kosiyachinda 1975; Fitzell & Muirhead
1983). However, optimum temperatures are specific for
different cultivars and in different regions. For example,
New Zealand 'Hass' avocados stored under appropriate
South African recommendations (Hass from KwaZulu/
Natal) were affected by more rots than the standard New
Zealand post-harvest temperature regime (Hopkirk et al .
1994). Storage in 2% O 2 and 5% CO 2 extended the
effective storage of 'Hass' avocados to 4 weeks, but rots
were severe (Hopkirk et al . 1994). High concentrations
of CO 2 (10%) prevented development of anthracnose for
3-4 weeks in 'Fuchs' and 'Waldin' fruit stored at 7.2°C
(Spalding & Reeder 1975).

Control measures
Darvas et al . (1990) showed less stem end rots and more
anthracnose due to snap picking 'Fuerte' avocado fruit, and
that removing the pedicel delayed ripening, which may
account for the increase in anthracnose rots. Tingwa and
Young (1975) showed that removing the pedicel increased
the rate of ripening in avocados in California. More rots
resulted in snap picked fruit in 'Hass' fruit in New Zealand
(Hartill & Sale 1991).
In order to minimise post-harvest diseases of avocados
an integrated disease management needs to be imple-
mented. Both pre-harvest and post-harvest protocols and
procedures are important for their control. A basic
understanding of the infection processes and the
periods of highest risk for infection to take place are
required, in order to more effectively use control
procedures. Development of prediction models in the
orchard for calculation of periods of infection risk is a
valuable tool, to enable growers to more effectively target
spray applications and thus reduce costs, and reduce the
risk of resistance to chemicals. Post-harvest handling,
especially temperature and ripening control should be
optimised. Sanitation in the pack house is necessary. Pre-
harvest control methods for post-harvest fungal decay
include good orchard sanitation (removal of mummified
fruit and dead wood) and effective pre-harvest fungicide
application such as copper which is widely used in some
countries where humid growing conditions prevail.
Harvesting should not be carried out in the rain or when
fruit are wet, and careful handling to minimize skin
damage helps to reduce rots. Snap picking of fruit can
reduce stem end rot incidence in dry periods but it can
result in increased rots in humid growing environments or
when harvested in wet conditions.
The most important post-harvest factor for reducing rots
is that of maintaining optimum temperature during handling,
storage, transport, and ripening. It is also critical not to store
fruit for long periods. Ripening fruit at lower temperatures
(15 to 20°C) can lead to significant reduction in rots