Very good control of aphids in barley was obtained with commercial-scale airplane applications as low as 5 Ibs of 10% Thimet granules (1/2 Ib actual toxicant) per acre. However, problems with hopper calibration, and the extreme accuracy in flying necessary to apply this low rate of the systemic insecticide, make a 71/2- to 10-lb rate of application more realistic. Chemical control of aphids on barley was found economical only when populations averaged significantly higher than 25 to 30 aphids per tiller. In seven southern California barley fields treated with Thimet granules (at 1 Ib of actual material per acre) the mean yield increase was 434 ± 128 Ibs per acre. Even at the lowest increase (306 Ibs per acre) the value of the extra yield was well above the cost of aphid control. The average aphid population in the check plots rose to 39 per tiller.