Effects of grass grub (Costelytra zealandicawhite) larvae on pasture plants

Abstract

Monocultures and various mixtures of perennial ryegrass (Lolium perenne L.) and cocksfoot (Dactylis glomerata L.), established at low and high plant densities in small pots, with and without 60 grass grubs (Costelytra zealandica White) per 30 cm2 were measured for 103 days. High density swards compared with low density swards suppressed tillering, but, over eight harvests, produced 42% more shoot dry weight and 53% more root dry weight. The ryegrass monocultures produced more shoot dry weight than other treatments, and the cumulative root/ shoot ratio increased as the proportion of cocksfoot increased. Grass grubs depressed total shoot weights by 40% but this depression showed little relationship either to plant density or the ryegrass/ cocksfoot ratio. At low densities, grass grubs suppressed ryegrass tillers more than cocksfoot tillers. Grass grubs depressed total shoot weights by 40% but this depression showed little relationship either to plant density or the ryegrass/ cocksfoot ratio. At low...