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www.agric.nsw.gov.au

Blight diseases inmangoes

The two main di sea ses of mangoes areanthracnose and bacterial black spot. This Agnoteexplains the diseases, causes, symptoms and the

pesticide program for their control.

ANTHRACNOSE

Anthracnose is a fungal disease caused byColletotrichum gloeosporioides. It is the most commondisease of mangoes on the north coast of NSW,devastating young leaves and often causingdefoliation of flush growth. If wet weather occursduring flowering, anthracnose causes severeblossom blight which can destroy inflorescences(flower panicles) and prevent fruit set. Fruit can

DPI-489 First edition 2004G. E. Stovold, Plant Pathologist

J. F. Dirou, District Horticulturist,NSW Centre for Tropical Horticulture,

Alstonville

be infected up to harvest but visual symptomsusually do not develop until the fruit begins toripen.

Spores of the fungus are produced from lesionson leaves, dead twigs, mummified inflorescencesand flower sepals. However, the major source ofinoculum for blossom blight is diseased immatureleaves. On leaves, spores are readily producedover a wide range of environmental conditionsand are dispersed by rain throughout the year.Infection of flowers depends on the temperatureand duration of surface wetness. Much longerperiods of wetness are required at lowertemperatures (1013C) than at higher

temperatures (2225C).Disease symptoms

Flowers

Black and irregular shaped spots grow andcoalesce to cause the death of flower panicles.

Leaves

New leaf growth is particularly susceptible.Initially, small, dark spots form and then theycoalesce to form irregularly shaped, dark, dry

lesions. The dead tissue often cracks and fallsout.

Symptoms of both anthracnose (left) and bacterial black spot(right) on mango leaves

A mango panicle infected with anthracnose disease

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Fruit

Anthracnose is usually only a problem in fruit that

is ripening, as the fungus remains dormant ingreen fruit during the growing season. Small darkspots form at first and then enlarge rapidly underfavourable conditions. Pink spore masses growon the infected tissue. Such fruit has no market

value.

Fruit can also show a tear-stained patternwhere the infection commences at the stalk-endand runs down the fruit.

BACTERIAL BLACK SPOT

Bacterial black spot is a bacterial disease causedby Xanthomonas campestris pv. mangiferaeindicae.

It can potentially be more damaging to flowersthan anthracnose. Leaf lesions consist of black,raised, angular areas, restricted by the veins andfrequently surrounded by a yellow margin.Elongated stem cankers occur on the bark andcan cause terminal dieback. Fruit lesions consistof individual or multiple star-shaped cracks, oftenappearing with anthracnose lesions in a tearstainpattern. Unlike anthracnose, bacterial lesions do

not expand as the fruit ripen.The disease attacks through natural openings

such as stomata, wax and oil glands, leaf and fruitabrasions, leaf scars, and at the apex of branchesin the panicle. Damage by adverse environmentalconditions such as frost and wind can also createsites for infection. In young trees the disease cancause dieback of branches.

PREHARVEST FUNGICIDE SPRAYPROGRAM

The spray recommendations for control ofanthracnose and black spot diseases in NSW areas follows.

From panicle emergence to fruit set (earlyAugust to end of October), apply a fungicideregistered for control of anthracnose (e.g.prochloraz, mancozeb) every two weeks and acopper fungicide registered for control ofbacterial leaf spot every three weeks. Begin thespray program with a copper fungicide.

From fruit set until harvest, alternate afungicide registered for control of anthracnose

with a copper fungicide every 1428 daysdepending on the weather. In dry seasons fewersprays are needed, saving time and pesticide.New flush growth should be sprayed duringautumn. This prevents a build-up of disease

on young foliage. Azoxystrobin (Amistar WG), a new

strobilurin fungicide, can be included in thespray schedule to improve control ofanthracnose. Include one or two azoxystrobinapplications at flowering and/or early fruit set,depending on the weather, at no less than 14day intervals and again at 21 and 7 days beforeharvest. Do not apply more than threeapplications per crop, or more than twoconsecutive applications.

POSTHARVEST TREATMENT OFFRUIT

It is absolutely necessary for North Coast mangogrowers to use a postharvest treatment beforepacking their fruit to control anthracnose ripe rot.

Cold water prochloraz. The breakdown rate ofprochloraz has not been determined so it is onlyapproved as a non-recirculated spray.Prochloraz is not effective against stem-endrot.

Spray fruit for 30 seconds. A spraying unit canbe made using two TX2 hollow cone nozzles

Anthracnose ripe rot affecting Kensington Pride fruit Fruit infected with bacterial black spot. Mango on the left isexuding bacterial ooze.

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mounted above the fruit on the packing line.An operating pressure of 320 kPa delivers 16L per hour.

Hot water carbendazim. Submerge fruit for fiveminutes at 52C. Maintaining the correctdipping temperature is critical to the success

of this treatment, so monitor the diptemperature carefully and regularly. Allow 3 Lof dip per kilogram of fruit. Agitate the tankmix to keep the fungicide in suspension andde-sap the fruit before dipping. Carbendazim

will also control stem-end rot.

Postharvest treatments will not providecomplete disease control. It is important to followfield spray recommendations to reduce the levelof postharvest disease, and to cool fruit promptlyfollowing harvest.

A fr ui t fly treatment is required for theinterstate movement of fruit. Dipping or a floodspray of either dimethoate or fenthion must bethe last treatment applied before packing.

CULTURAL PRACTICES AND TREEMANAGEMENT

All commercial varieties have some susceptibilityto anthracnose and bacterial black spot. Siteselection and planting density are important indisease control. Plantings should be located where

sunlight and good air movement will minimisethe duration of leaf wetness following rain, yetstop wind from damaging young shoots, whichpredisposes them to bacterial infection.

Pruning trees is extremely important. Thisshould be done to remove all sources of inoculumand to maximise air circulation and penetrationof sunlight.

Internal growth should be removed, leavingonly the peripheral foliage. Prune defoliatedbranch terminals and mummified inflorescences

during the growing season and clip spent fruitstalks during harvest.

Apply fertiliser sparingly and with caution. Toomuch fertiliser encourages a rapid leaf flush andif this occurs during periods of frequent wet

weather trees can become diseased. The best timeto apply fertilisers is immediately followingharvest so that trees produce an autumn flush.

FURTHER INFORMATION

For further information contact the authors or your

district horticulturist.

The State of New South WalesNSW Department of Primary Industries 2004

Edited by Bill NoadCommunications BranchDubbo, September 2004

Agdex 217/10Job No. 4830

DISCLAIMER

The information contained in this publication is based onknowledge and understanding at the time of writing(January 2004). However, because of advances inknowledge, users are reminded of the need to ensurethat information upon which they rely is up to date and tocheck currency of the information with the appropriate

officer of the New South Wales Agriculture or he usersindependent advisor.

Recognising that some of the information in thisdocument is provided by third parties, the State of NewSouth Wales, the author and the publisher take noresponsibility for the accuracy, currency, reliability andcorrectness of any information included

ALWAYS READ THE LABEL

Users of agricultural (or veterinary) chemical productsmustalways read the label and any Permit, before usingthe product, and strictly comply with the directions on thelabel and the conditions of any Permit. Users are notabsolved from compliance with the directions on the label

or the conditions of the permit by reason of any statementmade or omitted to be made in this publication.