Optimization of biological (Phasmarhabditis hermaphrodita) and chemical (iron phosphate and metaldehyde) slug control

Slugs are serious pests of a range of crops worldwide and are commonly controlled using chemical bait molluscicides. Phasmarhabditis hermaphrodita is a slug parasitic nematode that can be an effective alternative to chemical pellets. We conducted a field trial with Chinese cabbage to assess the potential of new nematode application techniques (dipping of root plugs, spraying around plant base and three low doses of P. hermaphrodita) compared to standard broadcast spraying of nematodes and chemical molluscicides. We also performed a series of miniplot trials investigating persistence of P. hermaphrodita, the efficacy of P. hermaphrodita compared to chemical molluscicides (iron phosphate and metaldehyde pellets) and using three repeated low doses of P. hermaphrodita compared to one broadcast spraying treatment. In field trials new application strategies of three low doses of P. hermaphrodita and dipping the plant roots in P. hermaphrodita reduced slug damage but did not reduce slug numbers. In miniplot trials we found that P. hermaphrodita persisted in soil and caused significant slug control 38 days after initial application. Also three low dose applications of P. hermaphrodita provided slug control comparable to one broadcast spraying. Also, we found that new chemical molluscicides such as iron phosphate can significantly reduce slug damage caused by Deroceras reticulatum and Arion ater.