This is not a caused by nutrition deficiency by it is a Sigatoka disease.
Sigatoka is a leaf disease, that significantly impacts banana yield by causing premature leaf death and affecting fruit ripening. To manage this disease, cultural control and chemical control methods should be employed.
Cultural Control: Regularly trim infected leaves, ensuring to remove more than 50% of the leaf area if it's infected. This should ideally be done weekly. After pruning, remove these leaves from the plantation to prevent further spread of the disease. Burning the pruned leaves is a highly recommended method of disposal as it kills the disease-causing spores. Additionally, remove any old infected leaves and burn them too.Ideally, convert the diseased or aging leaves into biochar, that enhances your soil quality and controls soil-borne diseases when activated.
Chemical Control: Fungicides can be employed to control Sigatoka, particularly in commercial plantations. Protectant fungicides like Mancozeb, Copper hydroxide, Chlorothalonil, and Banana misting oil can be used. Systemic fungicides, such as Triazoles (propiconazole, fenbuconazole, tebunconazole) and Strobilurins (azoxystrobin), can also be effective. However, remember to rotate the fungicides to prevent the fungus from developing resistance.