The effect of some invertebrate species on persistence of white clover in ryegrass swards

In two experiments in established swards of perennial ryegrass and white clover, plots were treated with pesticides to control slugs, leather‐jackets, weevil larvae and lucerne flea as selectively as possible. Other plots were treated to control ail of these pests. Chlorpyrifos application in early summer (to control weevil larvae) and methiocarb pellets (to control slugs) also gave partial control of leather‐jackets. Other effects on non‐target species were considered to be unimportant, as pest status could not be attributed to the species. A high level of control of lucerne flea by methiocarb pellets, noted previously, was confirmed. At both sites combined treatment against insect pests and slugs produced large increases in clover content and yield over a 3‐year period, in comparison with untreated plots, although clover tended to decline In alt plots. At one site, where the clover content of untreated plots reached 33% at one stage, specialist clover herbivores such as weevils and lucerne flea were more common. Treatments directed against weevils and slugs gave the highest clover yields, and leatherjacket control may also have contributed, particularly when the population reached 0.9 m ha −1 in the final year. At the other site, where the clover content was low (ultimately 01.1–6%), leather‐jacket populations reached 2.1 m ha −1 and slug numbers were also relatively high. Control of these species contributed most to the relative increase in clover content and yield.