Field Efficacy of Certain Biorational Pesticides against aphid, Aphis gossypii Glover (Hemiptera: Aphididae) on Watermelon, Citrullus lanatus Thunb. Matsum and Nakai

Watermelon, Citrullus lanatus is one of the most widely grown fruit crops in all parts of India. The cotton aphid, Aphis gossypii Glover was found to be the most destructive pest of watermelon in the early stage of crop growth. The aphid secretion of honeydew and development of sooty mould prevent the photosynthetic activity of leaves causing 45-75 % of seedling mortality. In this context, a field experiment was conducted to evaluate certain biorational pesticide against A. gossypii in watermelon. It was found that a significantly lowernumber of A. gossypii population (4.39 aphid/leaf) was recorded with the treatment of Azadirachta indica oil @ 3% followed by Beauveria bassiana (1x108 cfu spores @ 8 g /L) (6.01 aphid/leaf) and spinosad 45% SC @ 0.3mL/L (9.16 aphid/leaf), respectively resulting 92.89%, 90.27% and 85.17% reduction of A. gossypii population. Similarly, with the same trend the highest fruit yield (25.50 t ha-1) was recorded in the treatment of A. indica followed B. bassiana (24.43 t ha-1), spinosad (23.53 t ha-1) and lowest in the untreated check (16.30 t ha-1). The increase in fruit yield (56.44%) was recorded in the treatment of A. indica followed B. bassiana, (49.87%) and spinosad (44.17%). A maximum incremental benefit cost ratio of 1:2.84 was recorded in the treatment of A. indica followed by B. bassiana (1:2.74) and spinosad (1:2.68). From these findings it may be recommended that three rounds of application of A. indica oil @ 3% or B. bassiana (1x108cfu spores @8g /L) or spinosad 45% SC@ 0.3 mL/L at 15 days interval for the management of A. gossypii in watermelon