Influence of weather parameters on pod borers of pigeonpea (Cajanus cajan (L) Millsp.)

The experiment conducted at Regional Agricultural Research Station, Lam, Guntur during 2014-15 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. The male moth catches of H. armigera and S. litura were observed in 45th standard meteorological week (SMW) (Nov.5-11) and reached peak during 47th SMW (Nov.19 – 25). Second peak of S. litura was observed again in 52nd SMW (Dec. 24-31). The larval population of H. armigera and M. vitrata was observed in 45th SMW and reached peak during 50th SMW (Dec.10-16) which coincides with peak flowering stage of the crop. Highly significant correlation was obtained between pheromone trap catches of H. armigera and wind speed with correlation coefficient (r) being -0.637. Similarly, significant correlation was obtained with larval population of H. armigera and M. vitrata and morning relative humidity (RH I) with correlation coefficients (r) being -0.572 and -0.465, respectively. Hence, from the present findings it was concluded that as the morning relative humidity decreases the pest population increases and vice versa especially during flower bud initiation to flowering stage of the crop. 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.