Argentine stem weevil damage to high sugar ryegrass infected with AR1 under field conditions

Abstract

Previous laboratory based studies indicate that, compared to standard cultivars, high sugar grasses (HSG) can have lower endophyte and peramine concentrations and suggest that N fertilisation may result in further reductions in endophyte and alkaloid. This could reduce the resistance of HSG, particularly at high N inputs, to Argentine stem weevil (ASW), but the interaction needs testing under field conditions. The present objective was to determine the effect of ryegrass cultivar on ASW damage, and possible interactions with N fertiliser. ASW damage, endophyte and peramine concentration were measured in three perennial ryegrass cultivars, (HSG diploid, standard diploid and a tetraploid) containing AR1 endophyte, under high and no N fertiliser application. The proportion of tillers damaged by ASW adults or larvae did not differ significantly between cultivars. However, ASW adults tended (P<0.10) to prefer the standard diploid and tetraploid cultivars over the HSG cultivar. Our results are in keeping with previous observations that higher sugar diploid cultivars may have lower endophyte and peramine content than a STD diploid cultivar, but this does not appear to have reduced resistance to ASW. Lack of differences in N content of herbage leaves, between the N fertiliser treatments, likely due to compensating changes in clover content of pastures, meant little effect of N application was seen in this field trial.