Management of post-harvest mango diseases

In Australia, the most serious diseases of mango are caused by fungi. The majority of these diseases infect fruit in the field and the critical phases for disease control in mango production are during flowering and fruit set, and after harvest.

Post-harvest diseases can ruin an otherwise high-quality crop. With some post-harvest diseases, the damage occurs when fruit is ripening and ready for display to buyers. Other diseases show symptoms before harvest, so affected fruit can be culled during grading and packing.

Post-harvest disease control in mango is currently achieved through a combination of pre- and post-harvest fungicide application, orchard hygiene and post-harvest temperature management.

Inoculum of post-harvest diseases occurs on leaves, stems and flowers, so field control is important to reduce post-harvest losses. Post-harvest temperature management is also important because post-harvest diseases are favoured by temperatures above 25 °C during ripening.

During long-term storage of mangoes in a controlled atmosphere (5 per cent oxygen and 2 per cent carbon dioxide at 13 °C for three or more weeks), diseases appear that are not encountered in fruit stored for shorter periods. The cool temperature, high humidity and fact that fruit begins to reach the end of its storage life favour these pathogens.

Anthracnose

Anthracnose (caused by 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 post-harvest control measures are required.

Pre-harvest management

Spray with mancozeb at the label rate weekly during flowering and then monthly until harvest. Stop spraying 14 days before harvest. During dry weather, you can reduce flower sprays to fortnightly intervals.

If rain occurs during flowering, apply prochloraz at the label rate  in a tank mix with mancozeb. Prochloraz needs to be applied only every 3-4 weeks.

Copper oxychloride sprays at the label rate 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.

Post-harvest management

Unheated prochloraz spray can be used to control anthracnose. Prochloraz is not effective against stem end rot.

Apply prochloraz as per label recommendations 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.

Post-harvest treatments will not provide complete disease control.

Stem end rot

Stem end rot (Botryosphaeria spp., Lasiodiplodia theobromae and other fungi) is a soft, watery rot that develops from the stem end as fruit ripens after harvest.

Post-harvest management

The chemical fludioxonil is currently permitted for the management of stem end rot in mangoes. The permit specifies three use rates. A low rate for use in heated dip systems to be used when disease pressure is suspected to be low, a double rate for heated dip or flood spray systems when disease pressure is expected to be high and a higher rate that can be used as an ambient flood spray. Agitation and recharge is essential to maintain chemical levels in the treatment so consult the label for directions of use in your situation.

Do not use fruit from orchards with a history of stem end rot losses for long-term storage. The severity of stem end rot can be assessed in the following way.

Harvest 100 mature fruit at random from throughout the orchard. Leave them untreated and store at 25 °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.

Transit rot

Transit rot (Rhizopus stolonifer) appears after harvest and can cause sporadic fruit losses 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.

Post-harvest management

Remove reject fruit that 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.

No fungicides are approved for transit rot control in mangoes.

Other post-harvest diseases

A few other fungi (Aspergillus niger, Mucor spp. etc.) occasionally cause fruit losses during storage. They cause rots on the sides or at the stem end of fruit. Rough harvesting and handling can encourage these diseases. Careful handling and good hygiene measures will help manage these problems.

Export requirements

Choose fruit from orchards with low disease levels. Do not export fruit from orchards with a history of stem end rot or other diseases.

Where prochloraz is not acceptable to the importing country, export is not recommended unless fruit is treated with a combination of hot water and vapour heat. Vapour heat treatment was developed for export markets that require quarantine security against fruit fly but do not accept chemical disinfestation treatments. 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 before vapour heat treatment will improve stem end rot control.

Sanitation of packing equipment

Clean equipment daily with a steam cleaner or high-pressure hot water applicator. Otherwise, use a hose with a suitable detergent. Clean any equipment on which dirt and sap collects at lunch time as well as at the end of the day. If you are having a problem with fruit rots other than anthracnose or stem end rot, you may need to sanitise the equipment using a solution that is approved for use in a food business.