Yellow and black streaks with leaf spots spreading on my banana leaves (kela)

Small yellow streaks that turn into brown then black spots with grey centres, spreading on the leaves until they dry up, are most likely Sigatoka leaf spot, a fungal disease that thrives in humid, wet, crowded plantings. As the leaves die early the bunch fills poorly and fruit quality drops. Confirm with your KVK, since other leaf spots exist, but the pattern of streaks running into spots is typical. The most useful steps are cultural: remove and destroy badly affected lower leaves to cut the source of spores, keep proper plant spacing so air moves through, improve drainage, control weeds, and avoid overhead splashing that spreads the fungus. Balanced nutrition, especially adequate potassium, makes plants more able to cope. Where pressure is high, KVK-recommended fungicide sprays with typical actives such as mancozeb, propiconazole or a copper product, often with a sticker, are used, but follow the label, observe the pre-harvest interval, and rotate modes of action to avoid resistance. Mind residue and MRL limits if the fruit is for export. Get a local diagnosis before starting a spray schedule.