Integrated management of grass grub,Costelytra zealandica(White), in pasture using fensulfothion insecticide and nitrogen fertiliser alone and combined

摘要

Combinations of four rates of nitrogen (N) fertiliser and four rates of fensulfothion insecticide were applied to pasture in early autumn at three sites in northern Southland containing high (980/m2), medium (101#x2013;590/m2), and low (300/m2) densities of grass grub (Costelytra zealandica). The treatment producing the greatest additional dry matter (DM) of pasture per dollar invested for grass grub densities above 500/m2was either 0.5 kg/ha of fensulfothion alone which gave a 77 mortality of grass grub resulting in an increase of 9 kg DM/ha per day pasture in the autumn, or alternatively, 0.5 kg/ha fensulfothion combined with 25 kgN/ha producing an additional 19 kg DM/ha per day compared with control plots. At the sites containing less than 500 larvae/m2, 50 kg N/ha alone gave the best DM return per dollar invested. Pasture responses from N at sites containing high and medium densities of grass grub continued through to spring. There were no significant interactions between N and insecticide on pasture yield at any site. N had no significant influence on grass grub densities, proportion of developmental stages present, levels of diseased grubs, or white clover production. Recommendations derived from the trial results are that in pasture containing a grub density above 500/m2, apply 0.5 kg a.i./ha fensulfothion alone, or if the extra feed is required and the pasture is N-responsive, combine this with 25 kg N/ha. At densities below 500/m2use 50 kg N/ha if pastures are N-responsive.