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Differential susceptibility to pest damage in agricultural grasses

SUMMARY Plots were sown with six varieties of perennial ryegrass, one each of Italian, Westerwolds and hybrid ryegrass, and one each of cocksfoot and timothy, in April 1974. D.M. yield was assessed at four cuts each year, on plots receiving 300 kg N/ha annually, for 4 years. Invertebrate populations and plant survival were monitored at intervals. Half the plots were treated regularly from sowing onwards with the systemic insecticide, phorate. Insecticide treatment increased output generally, but the extent varied from year to year and between grass varieties. The persistence of Italian and hybrid ryegrass varieties was dramatically improved by insecticide treatment. The three diploid varieties of perennial ryegrass studied appeared to be less susceptible to pest damage than the three tetraploid varieties. Shoot-fly larvae (Diptera: Chloropidae) were the major obvious cause of damage.