Weather and its impact on population buildup of pod borers in pigeonpea

The experiment conducted at Regional Agricultural Research Station, Lam, Guntur during 2016-17 on pigeonpea (Cajanus cajan (L.) Millspaugh) yielded a good amount of information on the trend of population build up and seasonal abundance of gram pod borer, Helicoverpa armigera, spotted pod borer, Maruca vitrata and tobacco caterpillar, Spodoptera litura. Peak populations of H. armigera adults were observed during 37 and 45th SMW, whereas peak populations of S. litura adults were observed during 37, 42 and 46th SMW. The peak larval population of H. armigera and M. vitrata were observed during 39th SMW and 48th SMW, respectively which coincides with peak flowering stage. The correlation studies conducted between weather parameters and pest incidence showed that moderately significant correlation was obtained between adults of H. armigera and rainy days and sunshine hours with correlation coefficient (r) being 0.578 and -0.583, respectively. Moderately significant correlation was obtained between adults of S. litura and RH-II and rainy days with correlation coefficient (r) being 0.510 and 0.518, respectively. Further, moderately significant correlation was obtained between larval population of H. armigera and M. vitrata with sunshine hours with correlation coefficient (r) being -0.509 and -0.495, respectively. Thus, concluded that as the number of rainy days increase with decrease in sunshine hours the adult population of H. armigera and S. litura will increase. Similarly, the larval population of H. armigera and M. vitrata will increase as the number of sunshine hours decrease during the crop growing period. Thus, farmers can predict the pest early and optimize the application of insecticides in order to check the pest population from reaching the economic threshold level.