STRATEGIES FOR ARGENTINE STEM WEEVIL CONTROL: EFFECTS OF DROUGHT AND ENDOPHYTE

Abstract

Herbage production of several ryegrass cultivars was measured over two years at Wairakei and Rukuhia, under conditions of either Argentine stem weevil infestation or insecticide protection. Argentine stem weevil infestations Were similar at both sites and were negatively correlated with incidence of Acremonium loliae infection in ryegrass host plants. Ryegrass yields and tiller densities during periods of larval infestation in spring and summer were greatly increased by insecticide applications at Rukuhia but not at Wairakei. The weak nature of yield responses at Wairakei, despite high larval numbers, appeared related to drought conditions. Plant persistence was improved at Wairakei by these insecticide applications. Surveys of commercial sowings confirmed the correlations between incidence of Acremonium and Argentine stem weevil numbers and damage over a range of solI and management conditions. Between farm differences occurred, however, in the level of tiller damage These results are discussed in relation to strategies for control of Argentine stem weevll uhlising resistant ryegrass cultivars and insecticides. Keywords: Argentine stem weevil, Listronotus bonariensis, lollurn endophyte, ryegrass, tiller survival, drought, control strategies.