Determination of damage-yield loss relationships and economic injury levels of flower thrips on cowpea in eastern Uganda

Abstract

Studies were carried out in eastern Uganda to assess the effect of legume flower thrips ( Megalurothrips sjostedti) injury on cowpea grain yields and to establish economic injury levels (EILs) and action thresholds for thrips on cowpea. The studies relied on various insecticide spray regimes to obtain different thrips densities per experimental unit and use of exclusion cages in the field to confine defined numbers of thrips populations. A significant negative relationship ( y=−0.011 x+1.77; r=0.87; P=0.003) was observed in the field studies between thrips densities and cowpea grain yields. The EIL was established at seven thrips per inflorescence. The study also revealed that three well timed (i.e., applied after bud initiation to minimize flower bud abortion) insecticide sprays are effective in the control of thrips. The three sprays are regarded effective in that thrips densities were kept below the established thresholds. More than three sprays also reduced thrips populations to less than seven per inflorescence but these were not economical.