Effects of grass grub (Costelytra zealandica white)larvae on pasture plants

Abstract

Monocultures of perennial ryegrass (Lolium perenne L.), cocksfoot (Dactytis glomerata L), and a 1ȣ61 mixture of these two species were grown in wet and dry soil in small pots with and without 60 grass grubs .(Costelytra zealandica White) per 30 cm² for III days.

Over seven harvests, plants growing in wet soil produced more tillers, and 45%; more shoot dry weight than plants in dry soil. Root weights were generally similar in both soils. Shoot weights of ryegrass monoculture and the mixture were most depressed by grass grubs; the cocksfoot monoculture was least affected. In general the mixture behaved similarly to the ryegrass monoculture, and within the mixture grass grubs depressed ryegrass more than cocksfoot. The largest losses in shoot dry weights (60% to 70%) occurred 40 to 70 days after the grubs were introduced, but cumulative mean shoot losses were only 14% after 111 days.

More grubs survived in dry soil than in wet soil, and there were no differences in grub survival between plant treatments. In dry soil, grubs significantly reduced soil moisture.