Rolling pasture in May#x2010;early June depressed grass grub(Costelytra zealandica(White)) densities by crushing larvae feeding close to the surface. The relationship between rolling intensity and decreasing grass grub density was generally exponential. This initial depression (25#x2013;90) was followed by a further population depression during the pre#x2010;pupal and pupal stages. Rolling and pasture#x2010;treading by dairy cows in late July and August when larvae were deep in the soil profile, also depressed pupal densities. Marked reductions in grass grub densities were recorded following insecticide treatment (63#x2013;73) and differing rolling intensities (28#x2013;73) carried out in June. When both methods were combined, the reductions obtained were additive. Depressions in pest densities resulting from treading (69) in early July and rolling (65) in early August were similar and as with the combination of insecticide and rolling, were additive (93). Losses in pasture production and changes in botanical composition were minimal and significant only under the highest rolling intensity.
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