Biological control of ragwort does sheep grazing affect ragwort flea beetle

Abstract

Ragwort flea beetle (Longitarsus jacobaeae) (RFB) is present in many parts of New Zealand Its impact on ragwort mortality both alone and on ragwort trimmed to simulate sheep grazing was investigated Trimming reduced ragwort size and biomass throughout the trial More plants died in spring and summer but fewer plants died over the 12 month period in trimmed than untrimmed treatments Trimmed ragwort had fewer RFB larvae/g DM than untrimmed ragwort on only 1 of 3 occasions RFB at 123 RFB larvae/g DM in August did not affect ragwort mortality Low larval numbers were probably a result of high ragwort densities (up to 36/m²)