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Green-Seeds.com
Fruits
& Others
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Control of Postharvest Diseases of Mangoes
 Revised by A W Cooke
and K K Jacobi on behalf of L M Coates, Plant Protection Unit, Indooroopilly
and S N Ledger, Horticulture Postharvest Group, Hamilton
Information contained
in this publication is provided as general advice only. For application
to specific circumstances, professional advice should be sought. The Department
of Primary Industries Queensland has taken all reasonable steps to ensure
the information in this publication is accurate at the time of publication.
Readers should ensure that they make appropriate inquiries to determine
whether new information is available on the particular subject matter.
In Australia, the most
serious diseases of mango are caused by fungi, the exception being bacterial
spot. In mango production, the critical phases for disease control are during
flowering and fruit set, and after harvest.
Postharvest diseases
can ruin an otherwise high-quality crop. With some postharvest diseases,
the damage occurs when the fruit are ripening and ready to display before
buyers. Other diseases show symptoms before harvest so affected fruit can
be culled during grading and packing.
Control of postharvest
diseases in mango is currently achieved by a combination of preharvest and
postharvest fungicide application, orchard hygiene and postharvest temperature
management. Inoculum of postharvest diseases occurs on leaves, stems and
flowers so field control is important in reducing postharvest losses. Postharvest
temperature management is also important as postharvest diseases are favoured
by temperatures above 25°C during ripening.
During long-term storage
of mangoes in controlled atmosphere (5% oxygen and 2% carbon dioxide at
13 degrees C) for three or more weeks, diseases appear which are not encountered
in fruit stored for shorter periods. The cool temperature, high humidity
and the fact that fruit begin to reach the end of their storage life favour
these pathogens.
Anthracnose
Anthracnose (Colletotrichum gloeosporioides and occasionally C. acutatum)
is the major fungal disease of mangoes. Major losses occur from flowering
to fruit set and again after harvest. Sunken black spots appear on the
surface of the fruit during ripening. The disease is most severe following
periods of wet weather. Pre - and postharvest control measures are required.
Preharvest control 
Spray with mancozeb
(800 g/kg at 2 g/L) weekly during flowering and then monthly until harvest.
Stop spraying 14 days before harvest. During dry weather, flower sprays
may be reduced to fortnightly intervals.
Should rain occur during
flowering, apply prochloraz (462 g/kg) (Octave, registered trade mark),
using 1 g product/L in a tank mix with mancozeb. Prochloraz only needs to
be applied every 3-4 weeks.
Copper oxychloride sprays
(4 g/L) used for bacterial black spot control also control anthracnose,
however copper oxychloride should not be used during flowering. Where bacterial
black spot is serious, copper oxychloride can be substituted for mancozeb
sprays after flowering.
Postharvest control
Hot carbendazim
Hot carbendazim (registered
trade mark Spin Flo, manufactured by Rhone-Poulenc) is now registered for
postharvest treatment of mango in Queensland, Northern Territory, Western
Australia and New South Wales. Spin Flo is a liquid formulation containing
the active ingredient carbendazim.
Dip fruit within 24
hours of harvest by totally submerging them for 5 minutes in hot water (52
degrees C) to which has been added 100 mL product /100 L water. Lowering
the temperature of the dip below 52°C will reduce the effectiveness
of the treatment.
Temperature must be
carefully controlled to within 0.5 degrees C to prevent fruit damage. Use
an accurate thermometer to monitor temperatures in various parts of the
dip during use, especially near the heat source. Many growers use specially
designed tanks heated by gas or electricity with manual or thermostatic
temperature control. With an approximate ratio of 3 litres of dip to 1 kg
of fruit, no appreciable temperature drop occurs when fruit is added to
the tank. This dip also partially controls stem end rot.
Notes on dipping
Vigorous agitation before
and during dipping by means of a powerful recirculating pump is recommended
to keep the fungicide suspended. This is preferable to stirring or paddling.
Agitation also helps distribute heat from the heating element.
Bleed sap from fruit
before dipping. Mango sap affects the stability of the fungicide suspension.
Replace the dip once
it becomes contaminated by sap and dirt or after 3 days continuous use or
after 4000 trays have been treated. Prewashing fruit helps to prolong dip
life.
Dipping temperatures
should not exceed 52 degrees C as this may result in skin damage. Allow
fruit to cool before brushing. During wet weather, reduce the dipping temperature
to 48 to 50 degrees C as susceptibility to skin damage increases. Disease
control will be reduced at these lower temperatures.
Unheated prochloraz
Untreated prochloraz (Sportak, registered trade mark) spray to control
anthracnose can be used as an alternative to dipping in hot carbendazim
(Spin Flo).
Prochloraz is not effective
against stem end rot.
Apply prochloraz 45%
at 55 mL/100 L of water at ambient temperature. Prochloraz has been approved
for use only as a non-recirculated spray over fruit. Complete coverage of
the fruit is essential for effective control.
Dimethoate may be mixed
with prochloraz for fruit fly treatment for Victoria, provided fruit remain
wet for one minute.
Postharvest treatments
will not provide complete disease control.
Stem end rot
Stem end rot (Dothiorella dominicana and other fungi). A dark rot develops
from the stem end as fruit ripen after harvest. In fruit from drier areas,
stem end rot may be more serious than anthracnose.
Postharvest control
Avoid harvesting immature
fruit. Postharvest treatment with hot water and carbendazim (Spin Flo) is
partially effective against stem end rot. For control of stem end rot during
controlled atmosphere storage, a dual treatment of hot carbendazim (Spin
Flo) followed by prochloraz is necessary.
Fruit from orchards
with a history of stem end rot losses should be rejected for long term storage.
The severity of stem end rot can be assessed as follows.
Harvest 100 mature fruit
at random from throughout the orchard. Leave them untreated and store at
25 degrees C until they are fully ripe. Ideally, less than one-tenth and
certainly no more than one-third of the fruit should develop symptoms of
stem end rot by the time they are fully ripe.
Warning: The NRA has
indicated that at the end of the 1999/00 mango season (early 2000), the
off-label permit currently in place for postharvest treatment of mango with
benomyl (Benlate) for stem-end rot control will be withdrawn. The registered
product to treat this fungal disease is Spin Flo Systemic Fungicide, containing
carbendazim. Growers would be expected to use this fungicide following the
expiry of the current permit.
Transit rot
Transit rot (Rhizopus stolonifer) appears after harvest and can cause sporadic
losses of fruit under high humidity conditions. Pale watery lesions appear
and fungal growth may cover affected fruit. The disease can spread from
fruit to fruit and from contaminated packaging material such as wood wool.
Postharvest control of transit rot
Remove reject fruit
which may harbour Rhizopus from the packing shed. Spray packing equipment
and the shed with a sanitising agent. Steam cleaning or high pressure hot
water cleaning should precede the use of a sanitiser.
Wood wool should not
be used as packing material as it can act as a source of Rhizopus infection.
It also causes surface scratching.
No fungicides are approved
for control of transit rot in mangoes.
Other postharvest diseases
A few other fungi (Aspergillus niger, Mucor spp. etc) occasionally cause
losses in fruit during storage. They cause rots on the sides or at the
stem end of fruit. Rough harvesting and handling can encourage these diseases.
Hot carbendazim (Spin Flo) used for anthracnose control, careful handling
and observance of hygiene measures will help control these problems.
Export requirements
Choose fruit from orchards with low disease levels. Fruit from orchards
with a history of stem end rot or other diseases should not be exported.
Where carbendazim and
prochloraz are not acceptable to the importing country, export is not recommended
unless fruit are treated with a combination of hot water and vapour heat.
Vapour heat treatment was developed for export markets which require quarantine
security against fruit fly but do not accept chemical disinfestation treatments
such as ethylene dibromide. Vapour heat treatment will control anthracnose
during short term storage, but will not give adequate control of stem end
rot. Dipping fruit in hot water at 48-52°C for 5 minutes, 24 hours prior
to vapour heat treatment will improve stem end rot control.
Sanitation of packing equipment
Sanitisers should be
used after equipment has been cleaned. Steam cleaners or high-pressure hot
water applicators are very effective. Otherwise, use a hose and household
detergent. If possible, use chlorinated town water.
Spray packing equipment
with a sanitising agent such as:
(a) Chlorine solution
Use a solution containing 200 ppm (0.02%) available chlorine.
Notes
1. Sodium hypochlorite
(liquid)
Most preparations contain from 5% to 12.5% available chlorine.
For a 5% commercial solution, add 4 mL/L.
For a 12.5% commercial solution add 1.6 mL/L.
2. Calcium hypochlorite
(powder)
Contains approximately 30% active chlorine
First make a stock solution by adding 330 g of powder/L, then store in
a cool, dark place.
Add 2 mL stock solution/L
3. Monitoring the chlorine
level
Add 5 mL of wash solution to one litre of water, which should give a
solution of 1 ppm available chlorine.
Use a swimming pool test kit to check the concentration.
Warning
Chlorine may corrode steel and some rubber compounds if used continuously,
but 2 or 3 sprays a week should not cause problems. Avoid inhalation.
(b) Quarternary ammonium compounds (e.g. applied 3.300*)
Use 2 mL/L water. This product has a residual effect. Apply only to clean
surfaces. Avoid inhalation.
(c) Formalin
Use 20 to 50 mLs of formalin/L water. This is a potent product which is
unpleasant to use and should not be inhaled. In confined spaces, a full
face mask with the correct canister is recommended. Wear protective clothing.
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Green - Seeds Co., Ltd.
81/10B Ho Van Hue Street, Phu Nhuan District, Ward 9, Ho Chi Minh City, Vietnam
Tel: +84 (8) 847 6901 - Fax: +84 (8) 844 1392 - Email: info@green-seeds.com
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