Slugs & Snails

Phasmarhabditis nematodes.

Slug nematodes offer strong soil-based biological suppression...

About Slugs & Snails

Slugs and snails are major pests in UK horticulture, particularly in moist, protected and container-grown environments. They cause rapid destruction by rasping holes in leaves, damaging stems, eating seedlings and leaving silvery slime trails across plant surfaces. Slugs can travel long distances overnight and hide deep in substrate, irrigation lines or trays, making them difficult to manage with cultural controls alone.

Symptoms of Slug & Snail Damage

• Large, uneven holes in leaves and soft tissue
• Missing seedlings or chewed growing points
• Silvery slime trails across foliage and benches
• Feeding damage at night or early morning
• Disturbance of shallow-rooted cuttings or soft liners
• Rounded rasping marks on fruit or stems

Why Biological Control Works

The nematode Phasmarhabditis hermaphrodita is a highly effective biological control agent for slugs. Applied as a drench, the nematodes actively seek out slugs in the growing media, entering through natural openings and causing infection. This method is extremely reliable in propagation units, polytunnels, containers and raised beds where slugs hide below the surface. It also avoids the residue and wildlife risks associated with metaldehyde or ferric phosphate pellets.

Common UK Slug & Snail Species

• Deroceras reticulatum (Grey field slug)
• Arion hortensis group (Garden slugs)
• Arion vulgaris (Spanish slug)
• Cepaea spp. (Snails damaging ornamentals and young plants)
• Limax spp. (Large slugs feeding at night)

IPM Recommendations

• Apply nematodes preventatively during warm, moist periods
• Maintain compost moisture to maximise nematode movement
• Lift trays occasionally to check hiding sites
• Use copper barriers or rolled-edge pots for physical exclusion
• Improve drainage and airflow to reduce humid hotspots
• Remove moss, algae and debris frequently

Preventative vs Curative Strategy

Preventative:

• Introduce nematodes early in the propagation cycle
• Treat areas with known historic slug activity
• Maintain slightly moist media for nematode mobility

Curative:

• Apply full-rate nematodes when fresh damage is seen
• Check under pots, benches and trays for hidden adults
• Combine with manual removal where feasible
• Consider a follow-up treatment after 4–6 weeks in high pressure

Environmental Notes

• Nematodes require moist substrate to infect slugs
• Optimal temperatures: 5–20°C depending on product
• Do not allow treated areas to dry out immediately after application
• Snails are less susceptible — focus treatment on slug-prone crops