Impact of time of sowing on pest damage to direct-drilled grass and the mode of attack by dipterous stem borers

Abstract

Pest populations usually fluctuate throughout the year resulting in concomitant variations in damage. In this study the effect of pest damage to direct-drilled grass sown on different dates was assessed. Damage was worst on autumn-sown direct-drilled swards, in keeping with previous work done on swards drilled into conventionally produced seed beds. Larvae of dipterous stem borers, e.g. frit fly, Oscinella frit, were the most prominent pest. These larvae arise either from eggs laid on or near emerging seedlings, or may migrate from a previous grass crop and cause great damage to newly sown swards. In the present work migrating larvae, although not necessarily the most numerous, caused by far the most damage. However, a key factor in determining the level of damage was the rate of growth of grass seedlings, rather than simply the size of the population of frit fly larvae.