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.