Field resistance to stem‐boring larvae (Oscinella spp.) of some ryegrass (Lolium perenne and L. multiflorum) cultivars when newly‐sown

In one experiment, 29 cultivars of perennial ryegrass (Lolium perenne) and 15 of Italian ryegrass (L. multiflorum) were sown in small‐plots. The proportion of tillers of each cultivar that were attacked by stem‐boring larvae (Oscinella spp.) was assessed and a large range in resistance found. In a second experiment with fewer cultivars, plots were split for with and without pesticide (chlorpyrifos) treatment to determine the impact of the larvae on tillers and herbage yield. As expected Italian ryegrass cultivars contained significantly more larvae. Response to the pesticide treatment was variable. The stage and rate of growth of seedlings at the time of attack by the larvae was important in determining the extent of damage.