Sweet potato is one of the most widely cultivated root crops in St Vincent and the Grenadines. In 2018, 4.7 million lbs (2.1 m kg) of sweet potato was produced. However, farmers in Queens Drive and Dorsetshire, two main production areas, have been experiencing severe crop losses caused by the West Indian sweet potato weevil. The larvae, which does the most damage, tunnels through the base of the stem (crown) and through the storage roots. In the storage roots, tunnelling produces chemicals called terpenes, which give the flesh an unpleasant taste.
To assist farmers, CARDI in collaboration with the Ministry of Agriculture, established a demonstration plot in the affected area, to show by comparison the effectiveness of an Integrated Pest Management (IPM) strategy towards reducing damage caused by the weevil. A combination of cultural, mechanical and chemical tactics were found to be very effective in controlling the beetle. Some practices included field sanitation, the removal of alternative hosts – wild relatives of the Ipomoea genus and the use of insecticides to treat both planting material and soil.
The study plot was maintained alongside a control plot of minimal management inputs. Based on examination of 90 sample plants per study plot, there were marked differences observed between the results from the two treatment regimens. Weevil activity in each plot was estimated by number of larvae, pupae and exit holes (adults) on the stems (non-destructive sample) of each sample plant at time of harvest. The number of each stage of the weevil was significantly (P<0.001) lower in the IPM plot than in the unmanaged plot. The percentage of infested sample plants, was lower for IPM plot compared to control plot; 80% versus 100%. Consequently, there were no losses in marketable yield from the IPM plot due to weevil attack compared to 56.2 % weevil-damaged losses in the control plot. This demonstration will be repeated to substantiate the benefit to cost.
The IPM tactics employed in this study had effectively reduce the weevil population and damage to stems and tubers. This strategy will help sweet potato farmers manage this pest and improve an increase their productivity.