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Gastropods, slugs, snails, control, IPM
Slugs and snails cause significant damage to ornamental and crop plants in UK gardens and are the most common pest enquiry to the RHS Gardening Advice team. They constitute up to 6% of animal-related enquiries from RHS members. The plant destructive activities of slugs and snails in gardens have led to the development of a wide array of chemical, biological and cultural controls. Despite these control methods slugs and snails remain a persistent problem, this may be because the efficacy of the controls is unclear, there may be effects on non-target species and the environment, or there are perceived barriers to their successful use.
In order to improve the advice the RHS provides about slugs and snails in home gardens we have developed a research programme focused on their control. We have identified some key gaps in the knowledge and have set up projects in collaboration with BASF to address these.
A literature review is under way to assess the control methods available to manage slugs and snails in UK gardens using evidence from experiments published in the peer-reviewed scientific literature and from personal communication with relevant experts.
A field experiment has been set up with replicates at RHS Garden Wisley, Surrey and RHS Garden Harlow Carr, North Yorkshire. This experiment uses a randomized block design to assess the effect of the following treatments:
a. Control (no treatment)
b. Cultural management (mulch) – a loose covering of material on the soil around the plants
c. Cultural + synthetic chemical (metaldehyde) – the most commonly used type of slug pellets
d. Cultural + organic chemical (ferric phosphate) – a slug pellet that is certified as organic
e. Cultural + nematode biological control applied reactively (once damage is seen)
f. Cultural + biological control applied preventatively (applied regularly from the early spring)
The biological treatment is a product called Nemaslug® which contains the nematode species Phasmarhabditis hermaphrodita. This nematode is a specific parasite to molluscs, with no adverse effect on other types of animal. It works by entering the gastropod’s body and releasing a bacterium which stops feeding and causes a fatal disease.
Each plot will measure 2m x 2.6m (6.6ft x 8.5ft) and be bordered by a strip of lawn 1.2m (4ft) wide. There will be four blocks per site on two sites (ie. 48 plots in total).
In each plot a row of each of the following will be planted:
• Daffodils – the flowers are often eaten in the spring
• Hostas – these plants are a notorious favourite for slugs and snails
• Lettuces – the leaves are eaten and the animals contaminate the produce on harvest
• Potatoes – long-keeled slugs of the Milacidae family live underground and tunnel into potato tubers and bulbs
• Dwarf French beans – these can have their leaves damaged, which reduces the yield, or the beans themselves may be eaten
An assessment of number and species of slugs and snails in each plot will be measured weekly using refuge traps, from sowing/planting through to harvest. Leaf (all plants) and flower damage (daffodils only) will be recorded fortnightly. Upon harvest measures of fresh/dry matter yield (hostas, lettuce, potatoes and beans) and the presence of slugs and snails in produce (lettuces and potatoes) will be recorded. Environmental measurements such as soil moisture content will also be recorded and data from weather stations on-site at Harlow Carr and Wisley will be obtained. Overhead irrigation will be applied when weekly rainfall falls below a threshold.
The cost (treatment costs and application time) will be recorded to enable analysis of the cost effectiveness of the control method.
The RHS will be able to provide up-to-date advice for management of gastropods in UK gardens, with control strategies that combine the most effective methods under different scenarios.
We will publish the results of this experiment in a scientific paper and write pieces for The Garden and other gardening press. We will use our new knowledge to update the advice we provide to gardeners.
Advice on slugs
Advice on snails
Nemaslug ® and Nemasys product range
Read a blog about preliminary findings of this research
The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.