Agriculture Reference
In-Depth Information
Alternaria rot (
Alternaria alternata
), anthracnose (
Elsione
ampelina
,
Glomerella cingulata
), bitter rot (
Greenaria
uvicola
), black rot (
Guignardia bidwelii
), Botryodiplodia
rot (
Botryodiplodia theobromae
), Cladosporium rot
(
Cladosporium herbarum
), Coniella rot (
Coniella diplo-
diella
), Phompsis rot (
Phomopsis viticola
) and ripe rot
(
Botryosphaeria ribis
and others) (Snowdon 1990).
Botrytis cinerea
. A CT of at least 100 ppm-hour is the
minimum required to kill spores and mycelium of
Botrytis
at 0°C (32°F) or approximately 30 ppm-hour at 20°C
(68°F). The CT-100 dose can be obtained with an average
concentration of either 100 ppm for 1 hour, 200 ppm for ½
hour, 50 ppm for 2 hours or an equivalent combination of
concentration and time. This finding was the basis for the
development of the total utilization system.
The total utilization system differs from the traditional
system in that there is no excess SO
2
fumigant at the end of
the fumigation treatment, reducing both air pollution and
sulphite residues in the fruit. It can be used with forced
air cooling for initial fumigation and in cold storage for
subsequent periodic treatments. Total utilization typically
uses about half as much sulphur dioxide as the traditional
method, and improves uniformity and effectiveness of the
SO
2
fumigant. Details on this work are available in the
Luvisi
et al
. (1992). Inexpensive SO
2
dosimeter tubes are
available to enable fumigant penetration and distribution to
be monitored in store. These dosimeters were originally
designed for human safety monitoring.
When grapes are loaded for transport/shipment they
may receive an additional SO
2
fumigation before loading
to assure a longer market life because fumigation is seldom
available in receiving markets. During ocean shipment
period longer than 10 days or long retail handling in which
SO
2
fumigation cannot be applied, the use of SO
2
generat-
ing pads in combination with a box plastic liner is advised
(Crisosto
et al
. 1994). Sodium or potassium metabisulphite
is incorporated into the pads, allowing the release of SO
2
when exposed to moisture during transit and marketing.
The amount of SO
2
released is also affected by the
temperature and the effective use of these pads depends on
a good cool-chain being maintained. Dual-release pads
give a rapid initial release of SO
2
from part of the pad while
another part of the pad releases SO
2
slowly over a period of
8-10 weeks (Mustonen 1992). In France has been reported
that SO
2
levels within the carton usually reach approxi-
mately 10 ppm within the first week of cold storage and
then stabilise at around 2 ppm (Vidaud
et al
. 1993).
A special low dosage has been developed for fumigation in
trucks and overseas containers (Crisosto
et al
. 2002b).
Unless SO
2
fumigation is available, the receiver must order
grapes for immediate needs, and must complete distribu-
tion and marketing within a reasonable time after arrival.
General disease control
Strict hygiene in the vineyard is necessary to minimise the
amount of crop debris on which fungi can survive and form
spores. Thinning of bunches helps to prevent overcrowding
of berries and the resultant cracking which allows ready
infection. Pre-harvest fungicide sprays can give some
control of post-harvest fungal infections (Snowdon 1990).
It is recommended not to harvest until at least 3 days after
rain. After this period, berries infected with grey mould and
other fungi should be visible and can be removed during
bunch trimming. Harvesting tools should be disinfected
between rows of vines to reduce the transmission of viral
and bacterial diseases. After harvest it is vital to cool the
grapes as rapidly as possible and to handle carefully to
minimise injuries to the berries. Obviously a good control
of fungus development over the growing period is critical
for a good postharvest storage; however, a recent study sug-
gested that postharvest treatments are required even with
a good pre-harvest management (Smilanick
et al
. 2010).
Sulphur dioxide (SO
2
) fumigation
Table grapes are treated with SO
2
primarily to control grey
mould which is not inhibited sufficiently by rapid cooling
alone. Standard practice is to fumigate with sulphur diox-
ide immediately after harvesting and/or packing followed
by lower dose SO
2
treatments weekly during storage.
Usually this initial fumigation uses a high level of SO
2
(up to 5000 ppm) and may be carried out in specially
constructed rooms. Cold storage fumigation uses lower
concentration (2500 ppm or lower) and is carried out every
seven to ten days. In this traditional system the excess SO
2
is removed from the treatment chamber by venting or
scrubbing through water or sodium hydroxide aqueous
solution after a treatment period of about 20 min. Formulas
for calculating SO
2
fumigation dosages are available in the
publications by Nelson (1985) and Luvisi
et al
. (1992).
Recently it has been demonstrated that the amount of
SO
2
needed to kill
Botrytis
spores, or to inactivate exposed
mycelium is dependent on both the SO
2
concentration and
fumigation time. A cumulative concentration, calculated as
the product of the concentration and contact time, called
'CT product', describes the SO
2
exposure needed to kill
Problems with sulphur dioxide treatments
One of the problems associated with SO
2
fumigation of
grapes is the constant potential for injury to the berries
and rachis. Injured tissue first shows bleaching of colour,
