Efficacy of Brassica juncea granulated seed meal against Melolontha grubs

Abstract The grubs of Melolontha melolontha and Melolontha hippocastani damage the roots of many plants and are therefore considered serious pests in agriculture, horticulture and forestry in central and eastern Europe. Since the implementation of legislative regulations banning the use of synthetic insecticides against these pests in soil, alternative methods have gained high priority. The plants of the family Brassicaceae have recently received much attention due to the high content of glucosinolates (GSLs) in their tissues. The GSL breakdown products are highly biocidal in relation to many soil-borne pests. We tested Brassica juncea granulated seed meal against Melolontha grubs under semi-natural (the concentration-response experiments) and field conditions. The efficacy and the indirect lethal concentrations of GSLs that were necessary to obtain 50% and 95% grub mortality (ILC50 and ILC95, respectively) were estimated. The concentration-response experiments revealed that the ILC50 of GSLs dominated by sinigrin (97%) for the L1, L2 and L3 grubs was 118.4, 167.1 and 173.5 μmol/L, respectively, and the ILC95 was 293.3, 312.7 and 401.7 μmol/L, respectively. Under field conditions, the mortality of the L3 grubs in the plots that were treated with granulated B. juncea seed meal at ILC99.8 was almost twice as high (82.2%) as that of the grubs in the untreated plots (45.4%), and the changes in the grub density with time in these plots were significantly different. The results of our experiments demonstrate the high potential of soil biofumigation using B. juncea granulated seed meal to control Melolontha grubs.