Yam Mosaic Disease
This causes lesions on the leaves in a mosaic pattern. The plant withers and looks weak. It can cause stunted growth in the tubers, and they’ll have little starch content.
The best cure is prevention. Use slips resistant to this disease and ensure the area is weed-free during growth. Aphids spread this virus, so keep them under control. Otherwise, you can lose up to 50 percent of your yam harvest.
Leaves become dry, brittle and look burned. This is a fungus that overwinters in debris so ensure your planting area is free of plant material and the soil is rich and healthy.
Dry Rot Disease
This disease is caused by a nematode. When dry rot is present, the tubers have small lesions on the outside of the skin. As the disease progresses, the lesion deepens into the tuber causing cracking and rotting.
Use slips and tubers that are disease-free, rub tubers with wood ash prior to planting or practice good crop rotation. Try growing yams where you last grew chili peppers to help control dry rot.
These are little, flat bugs that leave behind a waxy substance. They suck the sap and moisture from the plant and excrete honeydew, which will attract ants and diseases like sooty mold.
Use neem oil at the first sign of the bug. You can also spray plants daily for a few weeks with diluted rubbing alcohol.
White Scale Insect
White scales appear on the tubers and often cause slow growth or even shriveling of the tubers.
Use a good quality neem oil or organic pyrethrum, as this is spread by insects.