Prospect of Tagetes erecta Linn. In Controlling Sweet Potato Weevil (Cylas formicarius Fabr.)

Sweet potato (Ipomoea batatas Poir.) is a root vegetable with a number of nutrient categories for the health benefits. In sweet potato cultivation, farmers often experience crop failure, one of which is due to pest attack caused by Cylas formicarius Fabr. weevil. Tagetes erecta Linn. (Tagetes) has been reported to have an insecticide effect on various pests that attack plants. The aim of this research was to evaluate the effect of Tagetes plant on the growth of I. batatas var. rancing (ubi cilembu) plant and the intensity of weevil attacks on ubi cilembu cultivation. The experiment was conducted in Desa Cigendel, Kabupaten Sumedang, West Java using randomized complete design. Treatments included TC (plot with Tagetes and Cylas), T (plot with Tagetes only), and C (plot with Cylas only) and K (plot without Tagetes and Cylas) as controls. Tagetes were planted around each plot and in each plot 20 Cylas/plant were introduced. Results showed that all treatments had an effect on the growth of sweet potato. The presence of Tagetes also reduced the intensity of pest attacks. The intensity of weevil attack on the plot of K, T, TC, and C were 34%; 9%; 16% and 62%, respectively, with an average number of Cylas per tuber were 38 larvae and 8 imago; 14 larvae and 6 imago; 15 larvae and 8 imago; and 72 larvae and 23 imago, respectively. Tuber dry weight in plot where Tagetes was added, showed an increase compared to control (T: 46.69 g, TC: 42.66 g compared to K: 37.69 g) while in plot C, tuber dry weight showed the lowest value of 34.90 g. Phytochemical assay showed that different plant organ contained different type of secondary metabolite, but only flower contained all secondary metabolites including alkaloids, terpenoids, phenols, tannins, flavonoids, and coumarin. GC-MS analysis on Tagetes root, shoot and flower extract showed that α-terthienyl (2, 2 ': 5 ', 2 ''-Terthiophene), which has been widely reported as one of the active compounds with insecticidal effect, present only in root and flower. From this study, it can be concluded that planting Tagetes around sweet potato plants can reduce the effect of Cylas on the growth of sweet potato as well as the intensity of pest attacks and α-terthienyl compound is likely to play a role in the reduction of pest attacks.