Fruit rotting after harvest

Fruit rotting after harvest

Anthracnose

Cause: The fungus Colletotrichum musae. Spores are produced on dead banana material and are spread to young fruit in water droplets. The fungus remains dormant in the tissue until the onset of ripening.

Solution: Handle harvested banana fruit with care to avoid damage. Apply appropriate post-harvest fungicide treatment.

 

Fungal growth seen on the cut surface of the crown.
Rot extending beyond crown and into fruit.

Crown rot

Cause: Several organisms can be responsible for causing crown rot symptoms. These include Musicillium theobromae, Fusarium equiseti-incarnatum (species complex), Colletotrichum musae and Thielaviopsis musarum. Symptoms can vary from fungal growth ‘fluff’ present on the cut crown surface through to complete breakdown of fruit.

Solution: Application of appropriate post-harvest fungicides will assist in minimising symptoms in the supply chain.

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Fruit rotting in field

Fruit rotting in field

Sunburn

Cause: Insufficient bunch shading during prolonged high temperatures. 
Solution: There is no cure for affected fruit. Maintain good canopy cover and ensure bunch covers are applied properly. It may be necessary to pull a leaf down over the bunch for protection. 

 

Affected areas are dark and in later stages are covered by ashy grey spores.
Close up of later stage covered by ashy grey spores.

Cigar end

Cause: The fungus Musicillium theobromae (formerly known as Verticillium theobromae). It enters the fruit from the dead floral parts and extends 10 to 20 mm into the fruit. 
Solution: Cigar end is a minor disease and specific control measures are not warranted. 
Bunch ripens prematurely in the field, making the bunch unmarketable.

Mixed ripe

Cause: Various stresses (severe leaf spot, pest damage, water and nutrition) reduce the rate of fruit filling. 
Solution: Improve crop management to limit stresses on the plant.

Punctures or splits on fruit

Punctures or splits on fruit

Birds or bats

Cause: Birds and bats landing on the bunch to feed on nectar from immature flowers.

Solution: Cover bunches promptly and use thick covers. For Lady Finger apply covers before any bracts lift on the bunch. 

Bell injection

Cause: Incorrect bell injection technique.
Solution: Train staff to inject slightly above one-third from the top of the bell. 
Symptoms show as slightly raised yellow spots on small fruit or longitudinal cracks on growing fruit. The exposed tissue collapses and turns black.

Diamond spot

Cause: The fungus Cercospora hayi. Spores are produced on dead banana material. 
Solution: Diamond spot is a minor disease especially where control of leaf spot is effective. 

Rust or bronzing on fruit

Rust or bronzing on fruit

Left: early damage appears as a water-soaked area on the skin between touching fingers. Right: later development showing typical reddish-brown rust.

Rust thrips

Cause: Feeding by Chaetanaphothrips signipennis from bract fall to harvest causes a rust brown skin discoloration. This symptom should not be mistaken for maturity bronzing, which is more prevalent on the outer exposed areas of the fingers. 

Solution: Soil treatments for banana weevil borer will help control the soil thrips population. Treat bunches at the time of bunch covering.

 

The bronze-red blemish on the curved fruit surface first appears at the 'three-quarter full' stage and becomes more intense and extensive as the bunch fills.

Maturity bronzing

Cause: Oxidation of cell contents, possibly from a water and nutritional imbalance, causes the epidermal cells to discolour, lift and break. 

Control: In the short term, bunches should be harvested early before symptoms become more severe. Avoid water and nutrient stresses in the plant.
Symptoms are similar to maturity bronzing but are associated with chemical burn from injection for scab moth. Symptoms are commonly seen on lower hands and may cross to fruit ridges.

Spray burn

Cause: Incorrect chemical application rates, problems with compatibility or environmental conditions.

Solution: Check that you are using registered chemicals and are applying them at the correct rates. Make sure that your spray application equipment is cleaned regularly. 
Note irregular silvery patches speckled with black spots. In severe cases the skin splits, causing longitudinal cracks.

Silvering thrips

Cause: Feeding by Hercinothrips bicinctus.

Solution: This is a minor and rare pest of bananas grown in north Queensland. No specific treatments are required.
Upper: banana (strawberry) spider mite causes red to purple-black surface discolouration to cushion end. Lower: two-spotted mite damage; webbing is usually present.

Mites

Cause: Banana (strawberry) spider mite, Tetranychus lambi, feeding on the fingers. More severe infestation will result in the damage spreading over the entire fingers. 

Two-spotted mites, Tetranychus urticae, feed primarily on the tips of fingers, causing silver-grey superficial damage. Webbing forms ‘bridges’ between heavily infested fingers. 

Solution: Severe mite outbreaks are usually the result of poor insecticide management, especially foliar application of disruptive pesticides that destroy beneficial species such as the Stethorus spp. beetle. Treatments with a suitable miticide may be required during periods of hot, dry weather when mite build-up can be rapid.
 

Spots of fruit

Spots on fruit

Note slightly sunken black circular spots up to 5 mm in diameter. Inset: banana spotting bug (about 2 cm long).

Banana spotting bug

Cause: Feeding (sucking) by banana spotting bug, Amblypelta lutescens lutescens, usually on the exposed outer curve of the fingers.

Solution: Damage is more severe on blocks adjacent to rainforest. No specific treatments required. If more than 5% of bunches are affected, spot spray.   

Fruit speckle

Cause: The fungi Colletotrichum musae, Fusarium oxysporum and Fusarium semitectum (formerly known as Deightoniella torulosa). Spores are produced in large numbers on dead leaf material during wet conditions and are spread in air currents to the fruit.  

Solution: Fruit speckle is generally a minor disease in well managed plantations that use a leaf spot spray program.  

Pin-head black spot

Cause: Rupturing of lenticels, most likely a reaction to environmental conditions, particularly water-logging and extended wet weather. This is often confused with infection by Deightoniella torulosa.

Solution: Ensure adequate surface and internal drainage for plants. Avoid planting in poorly drained soils. 

Note stings (minute pinholes) on the surface. A small drop of sap usually forms at the sting site.

Fruit flies

Cause: Banana fruit fly, Bactrocera musae, and Queensland fruit fly, Bactrocera tryoni, laying eggs (stinging) in the pulp of banana just below the skin. The banana fruit fly can sting green fruit but the Queensland fruit fly only stings ripening or yellow fruit.   
Solution: Chemical control should not be required since fruit is harvested at the hard green stage before either of the fruit flies can complete their life cycles. Do not leave over ripe fruit in the field. If mixed ripe fruit causes hot spots in the plantation, spot spray with an appropriate chemical. 
Note raised 'pimples' on the skin.

Flower thrips

Cause: Scarring from egg-laying by flower thrips, Thrips hawaiiensis on young fruit when still covered by the bracts.
Solution: Insecticide injection at bell emergence for control of scab moth also controls flower thrips. 
The spots or rings are usually on the lowest points of fingers where chemical runs if the bunch is oversprayed.

Spray burn

Cause: Spraying with excessive volumes of chemical or inappropriate chemical use. 
Solution: Use only registered chemicals and apply according to the label directions.

Sooty blotch

Cause: The fungus, Chaetothyrina musarum (formerly known as Chaetochyrena musarum)plus various fungi (moulds/mildews) growing on dead plant material during moist weather. 
Solution: Lady Finger and Ducasse are more prone to sooty blotch than Cavendish-type bananas. A post-harvest dip of sodium hypochlorite at 100 ppm for 5 minutes followed by immediate rinsing, is highly effective in removing sooty blotch.

Sooty mould

Cause: Sooty mould fungi that develop on the honeydew secretions of the banana aphid, Pentalonia nigronervosa.
Solution: Natural control by parasites and predators provides adequate suppression. Infestations are more obvious during cooler weather in autumn and spring. Spot treatment with a suitable pesticide is occasionally required as the mould can be difficult to remove from fruit. 

Scabs on fruit

Scabs on fruit

Surface feeding by the larvae causes scarring.

Scab moth

Cause: Larvae of Nacoleia octasema feeding on the fruit between the bunch stalk and the hand. Only occurs from bunch emergence to bract fall.
Solution: Newly emerged bells require pesticide injection while they are still upright. When the plants are growing quickly during summer, treat blocks at least weekly. 
Surface feeding by the larvae causes scarring.

Sugarcane bud moth

Cause:  Small grey larvae of Opogona glycyphaga. They feed and pupate mainly towards the tips of the fingers and where the flower end of a lower finger meets a finger in the hand above.
Solution: This pest lays its eggs on fruit after all the bracts have fallen. Treat bunches with insecticide during bunch covering. 

Banana fruit caterpillar

Cause:  Larvae of Tiracola plagiata feeding on leaves and fruit. Damage is usually confined to a few bunches and feeding on fruit is confined to the outside of fingers.
Solution: Although attack to a single bunch can be very severe, only a few bunches are damaged and specific treatments are not usually needed. Standard treatments for rust thrips and sugarcane bud moth help to control fruit caterpillar.  If damage is noted on more than 5% of bunches, treat with a pesticide. 

Corky scab

Cause:  Scarring from feeding and egg-laying by flower thrips, Thrips hawaiiensis on young fruit when still covered by the bracts.
Solution: Insecticide injection at bell emergence for control of scab moth also controls flower thrips.

Rub

Cause:  Rubbing between the bag and young fingers due to prolonged strong winds. Leaves rubbing against the fruit cause similar symptoms. 
Solution: Retaining existing vegetation or planting specific windbreak trees can reduce the damage caused by strong winds. 

Deformed or variegated fruit

Deformed or variegated fruit

Mokillo

Cause: The bacterium Pseudomonas sp. It occurs naturally on flowers and may be transferred to other flowers by insects. Frequently only one finger per hand is infected. The problem is more prevalent in the wet season. 
Solution: Control is not warranted.

Tissue-cultured off-type

Cause: A genetic abnormality occurring in tissue-cultured plants.
Solution: Destroy affected plants and set additional following suckers on nearby plants.
Fruit are usually short, straight and darker green.

Cold weather

Cause: Temperatures below 6°C lead to abnormal growth. The more hours of exposure and the lower the temperature, the greater the damage.
Solution: Very early bunch covering before bract lifting will raise the bunch temperature by 1 to 2°C.

November dumps

Cause: Bunch initiation coinciding with night temperatures below 6°C in winter. These bunches normally emerge in October and November.
Solution: Seldom a problem in north Queensland. Plant crops are affected more than ratoons, so time planting to avoid bunch initiation during mid-winter.

Genetic abnormality (variegated fruit)

Cause: A genetic abnormality that occurs in tissue-cultured plants.
Solution: Destroy affected plants and set additional following suckers on nearby plants.