Managing the white grub Phyllophaga spp. (Coleoptera: Scarabaeidae) affecting sweet potato, Ipomoea batatas L (Convolulaceae) in St Vincent and the Grenadines

Sweet potato (Ipomoea batatas L.) is a major export crop for St Vincent and the Grenadines, with 1,764 metric tonnes (valued at US$783,459.00) exported between 2004 and 2005. However, the production of sweet potato is severely affected by species of the sweet potato grub (Phyllophaga spp.) (Coleoptera: Scarabaeidae) which is the major pest of economic importance affecting the crop in St Vincent and the Grenadines. Damage to tubers caused by this pest is estimated to be as high as seventy percent of crop yields. Experiments were conducted at the CARDI Field Station (St Vincent and the Grenadines) using three sweet potato export varieties (Black Vine, Big Red and Lover's Name) to test the efficacy of three chemicals - Neem-X® (azadirachtin), Actara® (thiamethoxam) and Pirate® (chlorfenapyr)- in suppressing the pest population and resultant tuber damage. Treatments were allocated in a complete randomized block design and the insecticides were applied to the soil before and at early planting at the manufacturers' recommended rates. Nine treatments were evaluated and each was replicated three times over two planting seasons (2003 - 2004). Results obtained showed that plots treated with Actara® produced tubers with lower damage than the Neem-X®- and Pirate®-treated plots. These results are very promising as the use of these chemicals can be included as one component in an integrated management programme of the sweet potato grub.