Seasonal incidence of thrips and bud necrosis virus on watermelon

Studies were carried out during 2002-03 at the Indian Institute of Horticultural Research to understand the role of thrips and impact of insecticide application on the incidence of watermelon bud necrosis virus (WBNV). Seasonal variation in thrips number and WBNV was monitored through monthly sowing watermelon var. Arka Manik from December 2002 to June 2003. For every planting, two separate plots were maintained, one without pesticide intervention (control) and the other treated with acephate (75 SP) 500 g ai/ha at 10 days interval. A comparison between per cent WBNV incidence in treated and control plots indicated one hundred per cent WBNV infection at harvest irrespective of thrips number recorded. A field experiment was conducted to manage thrips on watermelon using a combination of synthetic and botanical insecticides. Among the chemicals evaluated, significantly less thrips incidence was observed when acephate (0.5kg a.i./ha) was sprayed at 10 days interval throughout the crop period. However, WBNV incidence was nearly same in all treatments. Another experiment was conducted to evaluate different synthetic and botanical insecticides in combination with black polythene mulch on thrips and WBNV infection. Covering the soil with black polythene, seed treatment using imidacloprid (Gaucho 75 WS 3g/ kg of seed) and acephate 500 g ai/ha spray at 10 day interval significantly reduced thrips infestation but not WBNV incidence. The results indicated that management of thrips does not effectively translate to WBNV reduction on watermelon.