Greenbug Control on Grain Sorghum and the Effects of Tested Insecticides on Other Insects1

Abstract

A new biotype of Schizaphis gramimun (Rondani) caused severe and widespread damage to sorghum, Sorghum bicolor (L.) Moench, in the summer of 1968. Screening tests and refinement of application rate studies were conducted in 1968 and 1969 to determine if compounds used in greeubug control on wheat could be used effectively also against this biotype. The most feasible chemicals, considering both insecticidal and nonphytotoxic properties, were disulfoton, parathion, diazinon, demeton, and ULV malathion. Carbophenothion, although somewhat slower acting, was also usually very effective. Supracide® ( S -((2-methoxy-5-oxo-∆2-l,3,4-thiacliazolin-4-yl) methyl) O,O -dimethyl phosphorodithioate), while not very effective in the 1968 studies, significantly reduced greeubug populations in the 1969 tests. Most of the insecticides were found to give reductions also in populations of the corn leaf aphid Rhopalosiphum maidis (Fitch). Fall armyworm, Spodoplera frugiperda (J. E. Smith), and flea beetle population differences following insecticidal treatments were not significant. Of the beneficial insects monitored, the primary species present were the convergent lady beetle, Hippodamia convergens Guerin-Meneville, and various parasitic Hymenoptera. In general the more effective the insecticide in controlling the greenbug, the greater its suppressive effect Avas on beneficial insect populations. However, demeton applied at 0.5 lb active ingredient per acre gave satisfactory greenbug control and spared much of the beneficial insect population.