What Is Wrong With My Yam?

Do the leaves have any small circular or irregularly shaped dry spots that are gray to straw in color?

Are the leaves mottled with yellow and green patterns?

Are the leaves curled and distorted, sticky to the touch?

Do the leaves and stems have white, cottony clusters on them?

Are the leaves covered with small white insects?

Are there any necrotic lesions beneath the skin, followed by yellow lesions below the outer skin of the tuber?

These symptoms indicate a fungal disease - Anthracnose. Keep plants dry when watering to prevent spread. Spray plants with copper when the first fruit develops if you have had problems in the past. Bordeaux mixture can also help to protect the plant from the disease.

Mottled leaves are caused by Mosaic Virus (Yam mosaic potyvirus). There is no cure for infected plants. Remove and destroy all flowers that have the symptoms of the mosaic virus. Mosaic virus is spread by aphids, so the best way of preventing the disease is to control these insects.

Distorted and sticky leaves and stems are caused by aphids. These tiny insects cluster under leaves and on growing tips where they feed on plant sap. Leaves, stems, and buds get distorted and later leaves and flowers drop from the plant. You can control them by washing them off the plant with water spray. Insecticidal soap should be used only with severe infestations.

White, cottony clusters on leaves and stems are caused by mealybugs. These tiny insects are covered with a fluffy white coating. They feed by sucking plants sap. They produce the sticky substance honeydew which makes leaves sticky. You can control them by washing them off the plant with water spray. Insecticidal soap should be used with severe infestations.

White scales are known to attack yams. Even though it won't affect yield sometimes foliage causes poor growth and tubers may show a delay in germination or even stopped. Severe infestation may lead to tuber shrivel. Control scales by spraying insecticidal oil during the growing season.

Yam nematodes cause a dry rot disease in yam tubers. There are no above-ground symptoms with yam nematode infestation. Use disease-free tubers/setts for planting. Treating tubers with hot water for 40 min at 120-130 degrees Fahrenheit before sowing and after harvest will reduce disease both in the field and storage.

Yellow, stunted plants and roots that have swollen galls indicate root-knot nematodes. Other symptoms are plants wilting during bright, hot days. Prevent root-knot nematodes by applying chitin or introducing parasitic nematodes to the soil before planting. Solarizing the soil also helps in preventing root-knot nematodes.