Evaluation of black vine weevil (Otiorhynchus sulcatus) control strategies using Metarhizium anisopliae with sublethal doses of insecticides in disparate horticultural growing media

Metarhizium anisopliae V275 was efficacious against black vine weevil when used alone or in combination with sublethal doses of imidacloprid or fipronil. Both control strategies were effective in peat, coir, bark and peat blends with composted green waste. M. anisopliae can be applied as drench or premixed into growing media. The former gave marginally better control. Over 98% control was achieved when M. anisopliae was applied with 1/10 dilution (sublethal rates) of fipronil. Marginally lower control was achieved when M. anisopliae was used with 1/100 dilution (sublethal rate) of imidacloprid. However, the latter combination gave better control than imidacloprid used at the recommended rate. More conidia were recovered from larvae exposed to sublethal doses of fipronil than imidacloprid and may explain the higher pest control since mortality is dose-related.