The clover root weevil in northern pastures: on-farm observations of its impact on white clover

Abstract

The clover root weevil (CRW) (Sitona lepidus) has had, over the last two years, a major impact on pastoral farming in the greater Waikato area. Research into CRW biology, damage profile and financial impact is continuing and far from complete. A survey of farms in the affected areas in 1997/98 yielded a large volume of on-farm observations. A survey of the impact of CRW on clover on a single farm produced data that estimated the cost of CRW to this farming operation. These anecdotal findings are combined with initial results from a glasshouse experiment. Damage by CRW tended to be less on lighter (ash and pumice) soils than on heavier, more water-retentive (peat and clay) soils. Drought reduced CRW egg survival and the ratio of first instar larvae to number of eggs hatched. Damage was greater under hard than lax defoliation regimes and increased with increasing rates of mineral nitrogen application. Red clover appeared to be less affected by CRW than white clover. The general picture suggested that the level of stress placed on the clover plant played a major role in the impact of CRW on those clover plants: the higher the stress levels the greater the impact of CRW. Keywords: clover root weevil, farm survey, pasture pest, Sitona lepidus, Trifolium repens, white clover