Leaves with dead edges or patches

Manganese toxicity (dead patches)

Cause: Excess manganese in the plant due to the presence of manganese nodules in the soil profile and water-logging.
Solution: Confirm the diagnosis with a leaf analysis. Improve soil drainage and soil structure. Avoid planting bananas in poorly drained soils.

Salt toxicity (dead edges)

Cause: A build-up of salt in the plant from high soil or water salinity.
Solution: Confirm the diagnosis with tissue or water analysis. Water heavily to leach salt out of the root zone. Seek alternative sources of water. Avoid excessive applications of fertilisers containing chloride.

Mites (dead edges)

Cause: Feeding of the banana spider mite Tetranychus lambi, or the two-spotted mite, Tetranychus urticae on the underside of leaves. Severe outbreaks are usually the result of poor insecticide management which has destroyed beneficial insects.
Solution: Treat with an appropriate miticide. Ensure adequate coverage to the underside of the leaves.

Water stress (dead patches)

Cause: Severe water stress during hot, dry periods.
Solution: Apply more water during periods of high demand. Water scheduling devices help to plan irrigation. 

Herbicide damage

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.