Black Sigatoka disease is caused by a fungus Mycosphaerella fijiensis and affects bananas. The fungus spreads spores that infect and destroy banana and plantain leaves. The leaves turn brown, plant energy reserves are depleted, and fruit production is greatly reduced. A native variant of the plantain is resistant to the disease, but is not acceptable to consumers because it is round instead of banana-shaped. Aerially sprayed fungicides can protect against the disease, but are too expensive for small-scale farmers.
Within 4 years in the 1980's, there was an 80% drop in plantain banana production in Costa Rica due to Black Sigatoka disease, which reduced the plantain crop from 26,000 to 5000 tonnes.