A study was conducted from 1958 to 1963 in the Imperial Valley, California. to determine whether the incidence of barley yellow-dwarf virus can be controlled with pesticides and whether direct feeding by the oat bird-cherry aphid, Rhopalosiphum padi (L.), and the corn leaf aphid, R. maidis (Fitch), caused sufficient barley injury to warrant the expense of insecticide treatment. Only an occasional barley plant that had virus disease symptoms was found, thus it was not possible to determine whether aphid control with pesticides could control the spread of the virus. Analysis of yield data indicates that in areas where barley yellow-dwarf virus is not a problem, or in years when the incidence of the disease is very low, yield increases above the cost of treatment may be expected when aphids are controlled at a level that is expected to average about 25-30 aphids per tiller. When aphids markedly rise above this level very substantial yields may be expected when aphids are controlled. Phorate (44D) seed-coat treatments were found to be unsatisfactory because of reduced seed germination and short-term control. Ten percent phorate granules at 7.5-10 lb/acre applied by airplane, followed by irrigation, gave excellent to very good aphid control.