If cassava plants leaves has black spots what is the deficiency and how you cure it?
Can you send a photo of the complaint. The usual problem in Fiji and elsewhere are brown spots caused by a fungus, Passalora henningsii. Used to be Cercosporidium henningsii, and before that Cercospora henningsii.
You can see a fact sheet on the Pacific Pests and Pathogens app. download it at the Google store (or Apple). It is no. 95
Grateful for a photo. And your name please