Sweet potato weevil causes extensive damage in the field as well as in storage.
Small white legless larvae bore tunnels in the tubers and inside vines. The tunnels are infected with fungi and bacteria that cause the tuber to rot.
Further, the larva feed on the internal tissues and deposit excreta within the tunnels rendering the tubers unfit for consumption.
About 165 eggs are laid in the hollows of stem/vines or tubers and hatching takes place with in 5-7 days.
Larval period lasts for 14 days and pupation takes place inside the plant lasting about a week.
The entire life cycle is completed in 6-7 weeks and there are 7-8 generations each year. Adult weevil measures 6-8 mm in length and life span is for 2-3 months.
This pest is disseminated from field to field through infested vines and carried over every season by breeding in damaged tubers left in the fields after harvest.
The pest is more abundant during monsoon and remains active throughout the year but population attains peak during March to May.
Adopt crop rotation and use resistant varieties. Select weevil free lands for sweet potato cultivation. Use weevil free planting materials of early maturing varieties.
Planting of deep rooting varieties and irrigating at 7 days interval control the infestation.
Earthing up the plants 50 days after planting reduces the weevil attack. Closing of cracks in the field by periodical hoeing minimizes the weevil infestation.
Mulching with Eupatorium odoratum leaves at rate of 3tonnes per hectare 30 days after planting suppresses the weevil attack.
After the harvest the field should be cleaned of trashes. Destruction of infested crop materials and crop residues help to lower pest population.
Trap the adult weevils using cross-cut sweet potato pieces of about 6 cm diameter (100g size) kept 5metres apart during 50 to 80 days after planting at 10 days interval.
Use pheromone traps at rate of 5 numbers per acre to attract and kill the male weevils.
Dip the planting slips in 0.05 per cent fenthion solution for 5 to 10 minutes prior to planting .
(J. Jayaraj, associate prof and R.K. Murali Baskaran Professor & Head, Dept of Entomology,Agricultural College and Research Institute, Madurai 625 104, phone: 0452- 2422956 Extn: 214)