Spots on leaves
Leaf spot (yellow Sigatoka)
Cause: The fungus Pseudocercospora musae (formerly known as Mycosphaerella musicola). Early stages of development appears as light yellow streaks 1 to 2 mm long. Streaks enlarge in time to become spots.
Solution: Ensure the leaf spot management program is carried out effectively. The program should include cultural (deleafing, drainage) and chemical (fungicides, oils, application timing, coverage) practices.
Cause: The fungus Paracercospora fijiensis (formerly known as Mycosphaerella fijiensis). In the early stages of development, black Sigatoka appears as rusty red streaks up to 5 to 15mm. These symptoms are more obvious on the underside of leaves. Streaks enlarge over time to become spots.
Solution: If you suspect black Sigatoka you must notify Biosecurity Queensland immediately (13 25 23). It is a notifiable disease and you must report any suspicious plants.
Biosecurity: Importation of all banana material (fruit, leaves, planting material) is prohibited without approval. A biological barrier is now established, reducing the number of susceptible bananas between the Torres Strait/Papua New Guinea, where the disease exists and the Far North Queensland banana production areas.
Cause: Several fungi including Mycosphaerella musae (banana leaf speckle or common speckle), and Ramichloridium spp. (tropical leaf speckle) can produce a range of symptoms. These fungi are spread by wind in moist weather and are more tolerant of cool conditions than the leaf spot fungus.
Solution: The leaf spot management program normally provides control of speckle. If better control is needed, apply fungicides by ground rig which targets the underside of leaves.
Cordana leaf spot
Cause: The fungus Cordana musae. Large numbers of spores produced on the underside of lesions are spread during wet windy weather. The fungus mainly enters the leaf through injuries. It is common on plants weakened as a result of water-logging or drought.
Solution: The leaf spot program provides adequate management of cordana leaf spot.
Southern cordana leaf spot
Cause: The fungus Cordana johnstonii. This disease is present in the tropics and distribution is limited. It is frequently seen on unsprayed Ducasse plants, and in areas of high elevation under cooler weather conditions. Lesion size is significantly smaller than Cordana musae, approximately 10 by 15 mm. As with Cordana musae, spores form abundantly on the underside of leaves on mature lesions.
Solution: The leaf spot control program should manage this disease.
Cause: The fungus Uredo musae. A disease with limited distribution, it is seen within plantations near tree lines and buildings which reduce spray coverage. Banana rust occurs predominantly on older leaves. Therefore fungicide applications should be applied via ground rig.
Solution: The leaf spot program should provide adequate management of rust.
Cause: Spray drift of contact herbicides such as paraquat onto the plant.
Solution: Avoid spray drift onto leaves. Affected plants should grow out of the symptoms.
Cause: Feeding by the banana spider mite, Tetranychus lambi, or the two-spotted mite, Tetranychus urticae, causes tissue to die, resulting in bronzed areas under leaves.
Solution: Treatment is usually not necessary because predatory beetles Stethorus spp. maintain adequate natural control. If these beetles are not present and monitoring results show the level of damage is severe, treat with an appropriate miticide. Ensure adequate coverage to the underside of leaves.
Cause: The scale insect Aspidiotus destructor sucking nutrients from the leaf cells.
Solution: Natural predation by beetles, parasitism by wasps and oil sprays used for leaf spot help to suppress scale. For small outbreaks, cut off affected leaves. Avoid the use of foliar sprays that will interfere with natural control agents. Specific insecticide treatments are not recommended or required.
Cause: The insect spiralling whitefly (Aleurodicus dispersus). The white adults and nymphs occur on the underside of the leaf. The name comes from the white trail in which the eggs are laid. Its sap-sucking reduces vigour, and the production of honeydew supports the growth of sooty mould which can cover fruit and leaves.
Biosecurity: Report all suspicious symptoms immediately to Biosecurity Queensland (13 25 23)