PEST MANAGEMENT DECISION GUIDE: GREEN AND YELLOW LIST
Sweet potato weevil
Cylas formicarius, C. bruneus Fukusi wa viazi vitamu in Swahili
- Plant uninfected clean tender vine tips (not the older parts) from uninfected fields. Avoid using tubers for planting as they may contain weevil larvae.
- Establish a nursery in an un-infected plot as a source of clean planting material.
- Dip planting material into a pesticide before planting (see yellow column)
- Use deep-rooted tolerant varieties such as Simama, Sinia, Mavuno, Ukerwe, Vumilia and others.
- Plant early in the main cropping season to give enough time for the crop to mature before dry period.
- Close soil cracks in the mounds by hoeing or earthing up around the base of the plants to stop the weevil entering soil to lay eggs or feed on tubers
- Harvest 3 months after planting to avoid cracks in dry soil where the weevils enter.
- Plant barrier crops around field, such as banana or cassava.
- Remove alternative hosts of weevils such as wild Ipomoea.
- Clean up all remains of the old crop, particularly infested vines and tubers, and destroy them e.g. by feeding to livestock. Do not bury remains as weevils can still survive.
- Do not store the remains near fields
- Rotate sweet potatoes 2-3 seasons with maize, pulse, or legumes
- Regularly check field for open soil cracks, about twice per month.
- The weevil adult is 6 - 8 mm long and has a long pointed mouth. It is black with a small red-brownish part, and can fly.
- Look for 1 to 5 mm long larvae that feed inside the tubers and make tunnels and holes.
- Monitoring of larvae and adults is very difficult.
- Pheromone taps might be used to capture male adults (2 traps/acre) or light traps, to detect presence of weevils.
- Larvae and pupae are hidden inside the tubers and adults hide most of their life inside the soil or tubers so cannot be reached by pesticides.
- Spraying insecticide on the ground is not effective because the chemical will not move into the soil to kill the weevils
- Wear protective clothing and follow the instructions on the product label.
- WHO class II (and Tanzanian red and yellow-label products) are not advised in Tanzania. Farmers are not allowed to buy or use WHO class II products without special permits and training.
- Always consult recent list of registered pesticides (MAFC / TPRI).
Use Cypermethrin–based products for preventively dipping tubers into the pesticides for 1-2 minutes before planting (but prefer vines/cuttings for planting); pyrethroid pesticide group.
WHO toxicity class II (moderately hazardous). High risk to bees, very toxic to aquatic organisms. Do not consume treated tubers and do not feed to livestock.
CREATED/UPDATED: October 2014
PRODUCED BY: Plantwise
©CAB International. Published under a CC-BY-SA 4.0 licence.