Grasses were sown as pure species and in mixtures with white clover (Trifolium repensL.) ‘Grasslands Pitau’ or red cloverTrifolium pratenseL.) ‘Grasslands Pawera’ for 2 mowing trials. The effects of populations of black beetle (Heteronychus aratorF.) and whitefringed weevil (Graphognathus leucoloma(Boheman)) on herbage yield and composition of the pasture were monitored over 3 years. Black beetle populations were at damaging numbers only in the first year of the trial and caused marked changes in pasture composition over summer and autumn in the ryegrass (Lolium perenneL.) ‘Grasslands Nui’ and ryegrass/white clover treatments. The ryegrass component was reduced by 36 in the ryegrass treatment with a 77 increase in weed levels. Black beetle feeding in the ryegrass/white clover treatment reduced ryegrass by 67 and increased the white clover component by 30. Populations of whitefringed weevil caused reductions of 25–45 in DM in the second and third years of the trial over summer and autumn with this effect carrying over into the winter and spring periods. Reduction in white clover yield of 52–77 in the grass-legume mixtures was the major factor responsible for DM losses. Red clover was extremely tolerant of whitefringed weevil feeding and populations remained low in the pure grass treatments.
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