Veggie Professor,
Root inefficiency caused by dry, chilled soil, commonly causes episodic nutritional deficiencies of zinc, copper, calcium, sulfur, etc.
The small or misshapened leaves are very susceptible to infections. I see mostly anthracnose--- grey-black --- and a few mango bacterial black spots--- coal-black.
Use mixed fertilizers with all the micronutrients, and use gypsum, and spray with copper and other micronutrients. Avoid the 0-0-52 fad.