Yam belongs to the family Dioscoreaceae. It is a root and tuber crop popularly grown in West Africa and it is rich in carbohydrates.
Cutlass is used to clear the bush or vegetation and heaps, ridges or mounds are made with hoe. It can also be done by ploughing, harrowing and ridging mechanically.
Varieties or Cultivars
Important varieties include:
- Dioscorea rotundata – white yam.
- Dioscorea alata – water yam.
- Dioscorea bulbifera – aerial yam.
- Dioscorea cayenesis – yellow yam.
- Dioscorea domentorum – bitter yam.
Climate and soil requirements: Yam requires a temperature of 25°C – 30°C; rainfall of between 100cm -180cm per annum; abundant sunshine and a well drained sandy-loamy soil, rich in humus.
Method of propagation/propagation materials: Yam is propagated by the following materials: yam setts, yam seeds or yam minisetts.
Seedrate: One seed yam or sett per hole; three to five tonnes of seed yam per hectare is required.
Planting dates: Early yam is planted between November and December, while late yam is planted between March and April.
Planting: Open a hole on the heap. Place one yam sett inside with the cut surface turned upward and slantly placed at an angle of 45° before covering it with soil. The cut yam sett should be dried under the sun and dusted with chemicals such as aldrin dust before planting. This prevents rottening and pest attack of the sett.
Spacing: Spacing is 90cm x 100cm, while yam mini-setts is 25cm x 100cm Sprouting occurs three to six weeks after planting.
- Mulching: This is the covering of the heaps or ridges with dry leaves to reduce soil temperature, conserve soil moisture and prevent rottening of yam setts.
- Regular weeding: This should be done regularly to control pests and reduce weed competition with crops for nutrients.
- Application of fertilizer: Apply 200kg (four bags) of N.P.K. fertilizer per hectare three months after planting, by ring method.
- Staking: The yam should be staked with strong sticks or bamboo. It ensures adequate exposure of the leaf surface to sunlight and increases yield.
- Training of vine: This is done regularly after staking to ensure even spreading and neatness of the vines to receive sunlight.
Maturity period: Yam matures in 8-12 months after planting.
Harvesting: Dig the soil gently with cutlass to remove tuber from the soil.
Processing: Yam tubers are processed into yam powder or flour or consumed locally.
Storage: Yam tubers are stored in barns. It can also be stored in form of yam flour and in dried peeled yam tubers.
Pests of Yam
1) Yam tuber beetle: The beetle makes holes on tubers, resulting in low tuber marketability.
- Apply insecticide like BHC at planting.
- Dust yam sett with aldrin dust.
- Practise crop rotation.
2) Yam shoot beetles: Young larvae cluster on vine tips. Adults feed on yam leaves and cause vine to die or defoliate.
- Spray yam plant with insecticides, e.g ., BHC.
- By hand picking.
- Dust with chemical like Agrocide 3 powder.
3) Rodents: Rats and rabbits eat up tubers.
- Set traps to catch the rodents.
Diseases of Yam
1) Yam mosaic disease: It is caused by a virus which is transmitted by a piercing and sucking insect.
Symptoms: Symptoms include a mosaic pattern and chlorosis of leaves. It causes stunting of affected plant.
- Grow resistant varieties Spray with insecticides.
2) Yam rot: It is caused by bacteria which are spread by splashes of rain and insects.
Symptoms: Liquid oozes out from infected tuber. White – brown liquid emits with pungent odour.
- Destroy all affected yam.
- Apply aldrin dust.
- Practise crop rotation.
3) Yam leaf spot: It is caused by a fungus (Cercospora spp) which is spread by wind.
Symptoms: Symptoms include dead spots on the leaves.
- Spray yam plants with appropriate fungicides.