Evaluation of Melia azedarach Linn Croton macrostachys Hochst and Schinus molle Linn Plant Extracts against Cabbage Aphid Brevicoryne brassicae Linn and their Natural Enemies Diaeretiella rapae (Mintosh)an
The objective of the present study was to assess bioactive potential of individual and combined effect of aqueous extract of Melia azedarach seeds, leaves of Croton macrostachys and Schinus molle against cabbage aphid Brevicoryne brassicae under laboratory and field condition. In the field, interaction of aphid predator, Hippodamia tredecimpunctata and nymphal parasitoid, Diaeretiella rapae was also observed in treated and control plot. The repellent activity of selected plant extracts was evaluated at 0.625, 1.25, 2.5, 5 and 10% concentration by using leaf disc no choice method. Field experiment was conducted at Bridge of Hope children village farm, Gondar, from October 2011 to January 2012. The selected plant extracts was tested in completely randomized block design method in the field. Six different solution, with 5% concentration was prepared from M. azedarach, C. macrostachys and S. molle and mixed forms such as M. azedarach (2.5%) + C. macrostachys (2.5%), M. azedarach (2.5%) + S. molle (2.5%) and C. macrostachys (2.5%) + S. molle (2.5%) and sprayed. The repellent activity was significantly greater in leaf discs treated with M. azedarach and S. molle at higher concentration. The number of infested cabbage plants and aphid population in the field was decreased significantly in plant extract treated plots. The aphids nymph parasitized by D. rapae and aphid predator H. tredecimpunctata population was decreased in treated plot. Total number of cabbage head formation and head weight was maximum in plot treated with M. azedarach followed by S. molle. These plant extracts are easily accessible and adoptable by farming community to protect their cabbage crops and also it could be one of the useful components for IPM program.