New Zealand Plant Protection 53 (2000), Biological control of ragwort - does sheep grazing affect ragwort flea beetle?

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New Zealand Plant Protection 53 (2000): 54-58

Biological control of ragwort - does sheep grazing affect ragwort flea beetle?

K. Betteridge, P.G. McGregor, D.A. Costall and P.G. Peterson

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 12.3 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).

Keywords: biocontrol, ragwort, integrated weed management, ragwort flea beetle (Longitarsus jacobaeae).