Seed coating with insecticide to improve oversown white clover (Trifolium repens L.) establishment in tussock grassland

Laboratory and field-screening experiments were carried out to evaluate a range of systemic insecticides for protection of white clover (Trifolium repens L.) seedlings from native broad-nosed weevil (Curculionidae: Brachycerinae) feeding damage, and for compatability with rhizobia. A laboratory bioassay showed that acephate, carbosulfan, oxamyl, thiodicarb, triaziphos, isofenphos, and lindane could reduce weevil feeding damage and increase seedling survival. When evaluated in the field, carbosulfan and isofenphos improved early seedling establishment more effectively than lindane and acephate. A commercially available white clover seed treatment, furathiocarb, increased seedling survival, and yield for up to 13 months after sowing, In the laboratory, carbosulfan, or its liquid carrier, caused rapid mortality of rhizobia whereas isofenphos and furathiocarb caused no significant mortality of rhizobia.