Several slug species are serious pests of agriculture and are difficult to control. One popular control method is the nematode Phasmarhabditis hermaphrodita, which has been used in slug control for > 25 years. However, there are reports of it failing to reduce slug numbers and damage in the field for unknown reasons. This may be due to lack of knowledge about how P. hermaphrodita performs when applied to different soils. We therefore assessed the survival, movement and pathogenicity of P. hermaphrodita infective juveniles (IJs) when added to six different soils (compost with and without peat, clay loam, loam, sandy loam and sandy soil). The soils were either frozen or autoclaved before use to eradicate resident nematodes prior to the experiment. P. hermaphrodita survived best in autoclaved compost without peat and in experiments with frozen soils, compost with and without peat was best. Survival of P. hermaphrodita was similar in other soils. Interestingly, in peat-free compost P. hermaphrodita reproduced prolifically, which may affect the long-term success of the nematode in the field as other life stages, apart from the IJ stage, cannot infect slugs. In infection experiments we found P. hermaphrodita added to compost with peat killed slugs faster than nematodes added to a sandy clay loam or sandy soil. In movement experiments, the nematodes remained within 3 cm of the application point in each soil. In summary, soil type severely affects P. hermaphrodita survival, and the ability to kill slugs; therefore it should be assessed by farmers and gardeners before use.

Several slug species are voracious pests of agricultural crops in northern Europe and are difficult to control. The parasitic nematode Phasmarhabditis hermaphrodita has been developed as a slug control product, but there is little information about whether it could be combined with other control methods (such as essential oils) to enhance its efficacy. Here, we carried out experiments in propagators with lettuce at three different time periods (July, September and October), and tested the following treatments: water (untreated control), cedarwood oil, P. hermaphrodita, cedarwood oil and P. hermaphrodita, and Tween 80 (used as an emulsifier for the cedarwood oil solution). Lettuce was grown in propagators with either 10 Deroceras reticulatum or 5 Arion vulgaris and the percentage of lettuce eaten over 14 days (as well as weight, the number of live slugs and eggs produced) was recorded. Cedarwood oil reduced slug damage, slug numbers and slug eggs in the experiments with D. reticulatum, and P. hermaphrodita performed well in two out of three experiments. The mixture of P. hermaphrodita and cedarwood oil was superior in reducing the proportion of lettuce eaten compared to single doses of each treatment in one out of three trials. In propagators with A. vulgaris all treatments performed poorly. In summary, P. hermaphrodita and/or cedarwood can be used to reduce damage by D. reticulatum, but are ineffective at controlling A. vulgaris. Slugs from the genus Arion continue to be a difficult group to control.