Herbicides compromise biological control of ragwort

In spite of ragwort flea beetle (RFB) being present on a Dannevirke dairy farm, pastures were sprayed each winter to reduce ragwort density and limit the risk of ragwort poisoning of stock. The trial on this farm from June 1999 - October 2001, aimed to determine whether herbicide (H) impacted on RFB and how H and RFB each impacted on ragwort growth and persistence. RFBfree areas were created by spraying with insecticide (I). Effects of ragwort on animal health are also reported. High ester 2,4-D (H) boom-sprayed once only, in June 1999, killed most ragwort plants and reduced RFB larvae densities to low levels before the plants died. Once new ragwort established in treatment H, the plants became infested with RFB larvae. RFB larvae were suppressed by I resulting in ragwort density declining more slowly than in treatments where RFB were not suppressed. Insecticide treatments were stopped after 15 months and, at 24 months, ragwort could not be found within the trial area. Ragwort control was attributed to the cessation of herbicide spraying allowing the RFB population to reach a sufficient density to kill both small and large ragwort plants. Sub-clinical ragwort poisoning was found in livers of culled cows that had grazed on ragwort-dense pastures. Keywords: animal health, biological control, Longitarsus jacobaeae, pyrrolizidine alkaloids, ragwort, ragwort flea beetle, Senecio jacobaea

Effect of plant condition on oviposition by ragwort flea beetle

The impact of grazing animals on oviposition behaviour of ragwort flea beetle (RFB) (Longitarsus jacobaeae) was investigated in two field experiments In the first trial manually damaged ragwort plants were exposed for 5 days to RFB In the second trial ragwort plants grown in sheep and cattlegrazed pasture were collected both in April and May 1997 for the counting of eggs on plants and in the surrounding soil Removal of the majority of ragwort leaves reduced egg numbers/plant whereas damage to leaves did not Similarly ragwort from sheepgrazed pastures which was smaller than ragwort from cattlegrazed pastures had fewer eggs/plant but a similar number/g fresh weight of ragwort High local humidity under rosette ragwort plants is suggested as the critical factor determining oviposition behaviour of RFB

Biological control of ragwort does sheep grazing affect ragwort flea beetle

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)

Responses of ragwort flea beetleLongitarsus jacobaeae(Coleoptera: Chrysomelidae) to signals from host plants

Responses of adult flea beetlesLongitarsus jacobaeae(Waterhouse), to signals from ragwort plants (Senecio jacobaeaLinnaeus) were studied by recording their directions of movement in a wind tunnel and their colonization of host-plants in the field. Starved beetle individuals, irrespective of gender, orientated toward upwind host-plants over a distance of 60 cm in the wind tunnel, whereas satiated beetles did not. In the absence of upwind host-plants, all beetles moved randomly in all directions, regardless of whether they were starved or satiated. Starved beetle individuals did not show directed movement towards hosts when plants were downwind in the wind tunnel, nor when in the presence of host-plants when the wind was absent. Groups of starved beetles orientated to upwind host-plants in the wind tunnel, as did individual beetles. In the field, plants over 60 cm upwind of the released beetles were found and colonized by more beetles than downwind plants, in spite of the presence of background vegetation. This confirms the result of laboratory experiments thatL. jacobaeaecan orient to upwind host-plants.