Bioeconomics of Russian Wheat Aphid (Homoptera: Aphididae) on Spring Barley in Northern Idaho

Abstract

<i>Bioeconomic models explaining the relationship between spring barley yield and density of</i> Diuraphis noxia <i>(Mordvilko) were determined by conducting caged field infestation experiments at 3 plant growth stages during 1992 and 1993 in northern Idaho. Barley grain weight per plant and number of kernels per plant declined as quadratic functions of aphid density at the two-leaf (ZGS=12) and flag-leaf (ZGS=39 to 41) plant growth stages. No significant yield loss occurred when plants were infested at flowering or medium milk stages. Infestations did not affect grain protein content. Economic injury levels (EILs) expressed as initial</i> D. noxia <i>density and as cumulative aphid-days were computed as functions of pest control costs, barley crop market values, and control efficacy. Given crop value of $2.00 per bushel and insecticide cost of $15 per acre, control is justified only when density exceeds 1.4</i> D. noxia <i>per plant at the beginning of 2-leaf stage spring barley. Expressed as aphid-days, control is warranted only if one expects pest intensity&gt; to exceed 26 aphid-days during the 14 d following the 2-leaf stage. EILs during the flag-leaf stage were derived for specific weather conditions, in particular, given barley valued at $2.00 per bushel and $15 per acre control costs, EILs during warm and dry• seasons are 7.6</i> D. noxia <i>per plant at the beginning of the flag-leaf stage (or 91 aphid-days per plant). Under the same economic conditions during cool and wet seasons, EILs during the flag-leaf stage are 4.2</i> D. noxia <i>per plant (or 63 aphid-days per plant).</i>