Rf. Vantoor et Kg. Dodds, ASSESSMENT OF GRASS GRUB (COSTELYTRA-ZEALANDICA (WHITE)) (COLEOPTERA,SCARABAEIDAE) DAMAGE IN RYEGRASS WHITE-CLOVER PASTURE IN SOUTHLAND, New Zealand Journal of Agricultural Research, 37(1), 1994, pp. 99-105
The effects of grass grub density on pasture quality and quantity unde
r sheep grazing were examined at three sites near Riversdale, central
Southland, New Zealand. Using insecticide for 2-3 years enabled pastur
es with low levels of grass grub and those with natural levels to be c
ompared. Grass grub reduced pasture production in autumn, winter, and
spring by 6.4, 8.0, and 4.4% per 100 larvae/m2 in April-May, respectiv
ely. Although grass grub caused occasional reductions in the proportio
n of ryegrass (up to 20% of sward) and white clover (up to 7% of sward
), during spring-summer, the long-term effect on pasture composition w
as minor. This information can be used to predict the value of pasture
lost and the economics of adopting a particular control option.