Summer of slugs

There’s something slimy going on at the RHS! We're after scientific proof in the battle to help gardeners get the better of slugs and snails

If you have seen our annual top ten pest list you may have noticed that slugs and snails have topped it nearly every year. Even when they’re not number one they’re a close second! There are countless recommended ways to stop these lettuce nibblers, including barriers such as gravel and copper, traps with beer or bait, biological control with nematodes, and pesticides in the form of bright blue slug pellets. Despite all this, slugs and snails are still a problem for gardeners, and many methods haven’t had much scientific work to confirm their usefulness. In response to this the RHS has launched a scheme of research into slug and snail control, which I am leading.

The first project is an experiment titled ‘Integrated Gastropod Management’ (IGM). Gastropods are single shelled, soft-bodied animals in the mollusc group of animals; which we know as slugs and snails. The name gastropod comes from the Greek words gaster, meaning stomach, and poda, meaning feet, and many a veg grower will agree that stomachs on feet summarises these animals quite well!

‘Integrated Pest Management’ essentially means using a combination of methods to control a pest, in order to achieve sustainable control (both economically and environmentally) and reduce our reliance on pesticides. This usually involves a strategy that has preventative as well as curative elements in it. The IGM project is being carried out in collaboration with BASF, who are the UK producers of Nemaslug® which contains Phasmarhabditis hermaphrodita – the nematode species that is used as a biological control for molluscs.

In this project I’m using five different combinations of gastropod control measures, plus a negative control (no treatment). These are:

  1. Cultural management in the form of a straw based mulch
  2. Mulch + metaldehyde pellets – the most commonly used type of slug pellets
  3. Mulch + ferric phosphate pellets – these slug pellets are certified as organic
  4. Mulch + nematode biological control applied reactively (once damage is seen)
  5. Mulch + nematodes applied preventatively (applied regularly from the early spring)
  6. No treatment – this is important to compare with the other strategies

Come to to RHS Gardens Wisley and Harlow Carr and see the experiments for yourself

These six treatments are being applied to plots containing rows of daffodils, hostas, lettuces, potatoes and dwarf beans. You can see a more detailed outline of the project methods, including treatments and plants used, plus a diagram of the plot layout here.

There are eight replicates of the treatments, four in RHS Garden Wisley and four in RHS Garden Harlow Carr, so you could even go and see it in action!

Further information

RHS Gastropod research project
Slug advice
Snail advice
Further information on biological control Nemaslug®
BASF company website


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