Agriculture Reference
In-Depth Information
environment (Norman 1988). The continuous use of synthetic
chemicals has also led to the proliferation of resistant
strains of pathogens (Archbald & Winter 1990, Eckert
1990). Different viable technologies have therefore been
developed as part of a holistic integrated control approach
and this can be achieved through effective pre- and post-
harvest management of diseases, improved handling,
transport, storage, packing and marketing. Alternative
post-harvest treatments can also be used in combination
with synthetic fungicides, such as the use of microbial
antagonists integrated with commercial chemicals (Droby
et al
. 1998), hot water (Obagwu & Korsten 2003), chloride
salts (Wisniewski
et al
. 1995), carbonate salts (Obagwu &
Korsten 2003), natural plant extracts (Obagwu 2003) and
other physical treatments such as curing and heat treat-
ments (Ikediala
et al
. 2002). Alternative post-harvest con-
trol options such as biological agents or natural plant
extracts have further become important since it is perceived
as being environmentally safer and more acceptable to the
general public (Janisiewicz & Korsten 2002). Whatever
treatment(s) that industry adopts, it must be more environ-
mentally friendly, safer for human health, economically
viable, able to minimise post-harvest decay and able to
extend shelf life to ensure successful trade in both the
domestic and distant export markets (Naqvi 2004).
mould on citrus (Eckert 1988). Resistance to thiabendazole
and imazalil is also widespread (Holmes & Eckert 1999).
This has further contributed to industry pressure to
introduce alternative protectants. Several new fungicides,
including the active ingredients fludioxonil and pyrimetha-
nil offer effective control of the pathogens that cause green
and blue mould,
Diplodia
stem-end rot and grey mould.
Fludioxonil is classified as a 'reduced risk' pesticide that is
based on having very low toxicity to humans and other
mammals, low risk of environmental contamination, a low
risk to soil and ground water contamination and is
compatible with integrated pest management practices
(Syngenta 2004). Pyrimethanil is also combined with other
fungicides, such as imazalil, with the advantage that they
have different single site modes of action. This combina-
tion provides effective mould control when used as a post-
harvest treatment on citrus (Vorstermans
et al
. 2005).
Spectrophotometry has been used effectively to set up a
feedback control system to control the variation of imazalil
concentrations in dipping tubs for citrus fruits (Altieri
et al
. 2005).
Preservatives or antimicrobial food additives
Preservatives or antimicrobial food additives are not gener-
ally considered post-harvest treatments but they do control
decay, and in some cases is the only option available for
producers. Some of these products include sodium benzo-
ate, the parabens, sorbic acid, propionic acid, SO
2
, acetic
acid, nitrites and nitrates and antibiotics such as nisin
(Chichester & Tanner 1972). The advantage of using such
products are that they are often used in the food industry,
are often considered as GRAS compounds, are cheap and
are able to integrate with other disease control strategies
(Molinu
et al
. 2005). Since the early twentieth century,
sodium carbonate and bicarbonate were investigated for
control of
P. digitatum
and
P. italicum
on citrus fruit
(Molinu
et al
. 2005).
Chemical control
In general, most fruit industry sectors have experienced a
serious reduction in registered available pesticides with
few new additions, if any. New EU and US legislation that
required re-registration of all pesticides introduced stricter
requirements in terms of health, environment and safety.
This necessitated major pesticide companies to focus on
major industries and the most important diseases. In gen-
eral, citrus pesticides remain important in the global arena,
despite growing chemophobia.
Pre-harvest applications
Pre-harvest fungicide applications are an effective approach
for control of post-harvest diseases, such as anthracnose
and stem-end rot on citrus as discussed in previous sections.
Nonchemical control
Biopesticides
The development of alternative post-harvest disease con-
trol options using either microbial agents (Conway
et al
.
1999; El-Ghaouth
et al
. 2000a; Korsten
et al
. 2000;
Janisiewicz & Korsten 2002; Pang
et al
. 2002; Ismail &
Zhang 2004) or natural plant products (Kubo & Nakanishi
1979; Dixit
et al
. 1995; Wilson
et al
. 1997; Obagwu &
Korsten 2003) have become more important as successful
commercial applications have gained ground. This alterna-
tive control strategy has the potential to be more environ-
mentally safe and more acceptable by the general public
Post-harvest applications
Several fungicides are presently used post-harvest for con-
trol of citrus decay-causing fungi. Examples of post-
harvest fungicides include thiabendazole, dichloran, and
imazalil. However, when compared to pre-harvest pest
control products, the number available to the industry is
limited. Build-up of pathogen resistance in the post-harvest
environment has also been reported for blue and green
