Management of Acyrthosiphon kondoi Shinji, blue-green aphid, and Therioaphis trifolii (Monell) f. maculata, spotted alfalfa aphid, by grazing and cutting lucerne

Abstract

Three experiments were carried out in New South Wales to assess the effects of grazing, forage harvesting and haymaking on populations of blue-green aphid (BGA) and spotted alfalfa aphid (SAA) and some of their predators. In experiment 1, at Tamworth, grazing by sheep at light, medium and heavy intensities reduced BGA numbers after 10 days by 52%, 74% and 93%, respectively, from the ungrazed control in dryland Hunter River lucerne. Grazing had no significant effect on the numbers of SAA and had little direct effect on the small numbers of predators present. A resurgence of both aphid species resulted in numbers significantly higher on regrowth in grazed areas than in the area left ungrazed. In experiment 2, at Tocal, grazing cattle on irrigated CUF101 at light, medium and heavy rates initially reduced BGA numbers by 30%, 53% and 75%, respectively, from their untreated levels. Grazing had little direct effect on the low number of predators present. In experiment 3, forage harvesting and mowing for hay reduced BGA and its predators more than did grazing at normal rates. It was concluded that while grazing or harvesting may reduce aphid numbers and damage initially, problems may result on regrowth.