Yams are a good source of vitamins and minerals and a popular food plant commercially and in home gardens. However, they do attract some pests and problems that plague them both before and after harvest. The best way to keep your yams "happy" and healthy in and out of the ground is to be aware of the signs of problems with major pests and diseases of yams. Knowing what to look for can help you avert a serious problem with your yam crop.
Powdery mildew looks like a heavy dusting of black, gray, white or pink chalk on the plant. It can attack the leaves, stems or the roots of yams. As soon as you spot the problem, use sterile pruning to remove any affected foliage and make sure that you are watering early in the morning so that water does not sit on the leaves. Dispose of infected leaf material in a sealed bag to prevent reinfection. Treat recurring infections with a fungicide.
Yam anthracnose is a fungal infection that can impact your yam plants in any geographic region. Leaves and shoots of the yam will blacken and die, resulting in stunted, small, deformed harvests. Anthracnose can be prevented using a fungicide with benomyl, but you need to remove affected plants and all plant debris from the field immediately in order to prevent the spread of the disease.
While these fungal infections originate in the fields, they often are not fully evident at the time of harvest and may carry on and spread during storage after harvest. If you notice soft, mushy spots or hard, dry, crumbly spots on the yams themselves at harvest, then remove these yams from the rest to prevent the spread of infection. You can prevent tuber rots by making sure that soil is well-drained and doing your best to minimize the physical damage to the tube during the harvest. Make sure that your storage areas are well-aerated. Bordeaux mixture can also help alleviate or eliminate this problem.