This archive report was first published on 10 January 2020.
By ANN MACHARIA
Sweet potatoes are a staple crop in many parts of the country, farmed under both irrigation and rain-fed conditions due to their adaptability.
However, some tubers may have black marks or tunnels, which can be a sign of infestation by the sweet potato weevil.
According to an agronomist, the weevil is the most common pest affecting the crop, causing significant destruction to the tubers.
Adult weevils feed on the leaves and vines of the sweet potatoes in the vegetative stage, causing the leaves to turn yellow.
They also lay eggs on the leaves and vines, and once the crop starts forming tubers, the weevils spread their attack.
The weevils normally search for exposed roots and get into tubers through exposed cracks in the soil.
Infestation of the tubers depends on the availability of cracks in the soil.
As they feed on the tuber, they lay eggs below the surface of the roots, causing damage that can result in high mortality cases in young plants.
The infested tuber often has tunnels that serve as entry points for infections, making them bitter and sometimes causing them to rot.
The vines also become thick, malformed, and tend to discolour, crack, and wilt.
To control the pest, farmers should create mounds or ridges incorporating fresh lantana camara leaves before planting the sweet potatoes vines.
This improves soil organic matter and serves as a repellent for the sweet potato weevil, increasing yields and the quality of the tubers.
Other control measures include effective crop rotation, sourcing clean planting materials, and planting resistant varieties.
Deep planting, regular filling of soil cracks, and irrigation can also help reduce infestation.
Additionally, mulching newly planted vines, intercropping with ginger or coriander, and timely planting can help control the pest.
Field sanitation, timely harvesting, and grading after harvesting and sorting are also essential in preventing infestation.
Other pests affecting the crop include millipedes and root-knot nematodes, while diseases such as sweet potato scurf can also cause significant damage.
