Determination of economic injury level of Sitobion avenae (Hom.: Aphididae) on wheat of Chameran variety in Ahwaz

The drought phenomenon in recent years has increased the oat aphid (Sitobion avenae Fab.) population in khuzestan wheat fields. Considering the existence of different natural enemies of this pest in cereal fields, the best control method would be based on selective pesticide application which is less harmful to environment and natural enemies. Thus determination of pest Economic injury level (EIL) became a necessity to prevent immethodical usage of pesticides in wheat vulnerable agroecosystem. Hence, an experiment was conducted in complete randomized block design based on split plot with two factors and three replications including growing stages and aphid density in Chamran cultivar in agricultural research station of Ahwaz during 2010 to 2011. Growing stages (Early, middle and late of milky stage) and aphid density (0, 5-10, 11-15, 16-20, 21-25, 26-30 and 31-35 aphid on spike) were considered as mainplot and subplot, respectively. All treatments applied in a net cage. Averages of yield in different aphid density treatments were grouped by Duncan- multiple range test. Regression equations and curves were obtained between aphid density and seed weight in each spike. Grain threshold method was used to EIL measurement. The results showed that EIL was 17, 22, 42 aphids/spike in early, middle and late of milky stage of wheat with no calculating of natural enemies but ET was 12, 17, 31 aphids/spike in the first year and EIL was 9, 18, 49 aphids/spike and ET was 7, 14, 37 aphids/spike in the second year. Also, EIL was 8, 16, 44 aphids/spike and ET was 6, 12, 33 aphids/spike in 2014-2015, respectively.