Effect of Argentine stem weevil on vigour of ‘Grasslands Roa’ tall fescue under dairying in the Waikato

Abstract

Surveys of Argentine stem weevil (Listronotus bonariensis (Kuschel)) populations and damage, and damage assessment studies, on ‘Grasslands Roa’ tall fescue (Festuca arundinacae Schreb.) were carried out on young pastures on peat soils in the Waikato in 1985 and 1986. Argentine stem weevil occurred in all pastures surveyed. Adult populations ranged from 19 to 279/m² and from 87 to 203/m² in autumn 1985 and 1986, respectively. The percentage of tall fescue tillers killed by stem weevil larvae ranged from 4 to 20% in 1985 and from 9 to 39% in 1986. Damage assessment studies at three sites showed that without insecticide protection, tall fescue tiller densities decreased throughout the summer and autumn. However, insecticide treatments failed to increase the dry matter contribution of tall fescue or total pasture production. The annual weed grass Poa annua L. was abundant in the pastures and supported high numbers of Argentine stem weevil larvae. The significance of Poa invasion in the deterioration of the tall fescue sward is discussed.

Keywords:

• Argentine stem weevil
• Listronotus bonariensis
• tall fescue
• Festuca
• Poa
• vigour
• tiller density
• tiller death