Economic injury level of Aphis craccivora Koch. in kharif greengram var. AAU 34.
The economic injury level (EIL) of A. craccivora populations in a kharif green gram crop (cv. AAU 34) was estimated in Assam, India during 1994-95. Graded levels of A. craccivora infestation were obtained by foliar application of phosphamidon 0.025% at fortnightly intervals. A. craccivora populations increased from 0.8 aphids/plant in the no exposure treatment to 77.97 aphids/plant in the full exposure treatment. This was highly correlated with a decrease in yield over the same period (r=-0.956 and -0.982 in 1994 and 1995, respectively; P=0.01). The yield infestation relationship revealed that every unit increase in A. craccivora population resulted in a yield loss of 3.54-4.68 kg/ha. EIL of A. craccivora population on green gram was calculated as 10-16 aphids/plant; under favourable conditions, such a population level may be attained in the field just one week after their appearance.