Hi Siddharta,
There are 2 main sorts of fungal diseases which can attack the leaves and in both cases the leaves blacken and the plants die. 1) Anthracnose is the one that is the most widely spread of the diseases. 2) Yam Mosaic Virus is the disease that causes the most damage.
The way to treat this problem is to remove the plants and destroy them immediately if possible. Sometimes the damage can be limited by a spraying with a fungicide but basically this does not really help and the longer they are left in the more problems remain for the following season .
Powdery Mildew is another disease that affects the plants. If afftected then prune the infected part and destroy. You can also use fungicides like dinocap 1g/l or any fungicide with a similar combination.
Yams are also prone to Yam Beetles, which burrow through the tubers and eat the flesh. These can be treated with an insecticide. Nematodes are a microscopic worm that causes a root restriction. Unfortunately there is no known cure and the yams need to be moved from the area.
Crop rotation helps keep the ground clear of pests and is essential for yam cultivation.
REgards
Ashwini S
