Economic Threshold for Pea Aphid

Abstract

Economic threshold for the pea aphid Acyrthosiphon pisum (Harris) was determined using an improved field pea variety, ‘Mohanderfer’ (1991-1993) and a local cultivar (1994-1996) at Kulumsa Research Centre of the Institute of Agricultural Research (IAR), Arsi, for six consecutive seasons, starting in 1991. The experiment was laid out in a randomized complete block design in four replications on plots 4 m long and 8 m wide. Maximum grain yield was obtained from plots fully protected from aphids and the lowest from unsprayed plots in all years. A calendar-based insecticide application was superior in all aspects. However, considering the cost-benefit ratio (CBR), one or two applications of pirimacarb recorded the highest at 35-40% level of infestation for ‘Mohanderfer’ and 40-45% for Arsi local. The highest CBR for ‘Mohanderfer’ at 35% infestation was 1:16 in 1991, followed by 1:6.73 at 40% in the
1992 season. The three years’ CBRs for the local were 1:2,14, 1:2.37 and 1:3,01. These results indicated that more than two sprays are not justified for the control of A. pisum on field pea.