Comparative study of sampling methods of the cabbage aphid, Brevicoryne brassicae (Hem.: Aphididae) on rapeseed plant, Brassica napus in Ahvaz region

The cabbage aphid, Brevicoryne brassicae L., is one of the major and economic pests of cruciferous plants in the world which has destructive effects on the rapeseed, Brassica napus L. In this research, for accurate estimating of the cabbage aphid population, three sampling methods (photography, measuring the average length of the infected stem and average weight of the aphid) as the main treatments were separately compared to direct count method, as the control treatment during budding, flowering and sheathing stages of rapeseed. For each stage, twenty-two canola plants were chosen and from each chosen plant, top stem covering completely by the aphids was selected as the sampling unit. The results showed that measuring the average length of the infected stem and average weight of aphid methods were significant difference with direct count method during budding, flowering and sheathing stages. However, there was no significant difference between photography and direct count methods during budding stage. Based on this, the photography method with maximum average of correction factor (0.790), coefficient of determination (0.9315) and relative net precision (RNP) (51.56) is the best and most accurate technique for precise estimation of cabbage aphid population during budding period. According to the obtained results of this study, choosing the correct sampling method at the right time can promote the integrated management programs of cabbage aphid.