Gastropod barriers

RHS project team

Hayley Jones, Emma Griffith and Gerard Clover

Start date

01/02/2018 00:00:00

End date

27/09/2018 00:00:00

Keywords

Gastropods, slugs, snails, control, barriers, IPM

The problem

Slugs and snails are a major problem for home gardeners and are generally the most common pest enquiry received by the RHS Gardening Advice team.

Many home gardeners choose to minimise pesticide use and, as such, barriers and repellents to gastropod damage are often suggested in gardening publications and discussions. For some barriers such as copper and copper salts, a number of scientific studies have demonstrated their efficacy in the lab, but there have been fewer field realistic tests. Several barriers, such as egg shells and bark mulch have not been studied scientifically.

Approach

The experiment was carried out at the Field Research Facility at RHS Wisley. The plant used in the experiment was a gastropod favourite, lettuce, and the experiment assessed the effectiveness of the following gastropod barriers and repellents: 

• No treatment

• Copper tape around pots and collars in the ground

• Sharp horticultural grit

• Pine bark mulch

• Wool pellets 

• Egg shells – washed, dried and crushed roughly

These treatments were tested under two different growing conditions; in pots on a small patio and in a raised vegetable bed. These two conditions were selected as they are common growing conditions and we expected that the barriers might have different effects when used in this way. The experiment had nine replicated blocks, each consisting of a paired patio and bed. The order of treatments was randomised within each block. The lettuces were grown under glass, three plants to a 2L pot, then placed out or planted out.

All barriers were applied either according to manufacturers’ instructions or as the consensus of gardening knowledge dictated. The substances were generally applied in a continuous ring around the plant (inside of the rim of the pot and in an equivalent circle on the plants in the ground). The copper was applied as a foil tape to the outside of the pots, and copper collars were placed around the plants in the ground.

The lettuces were kept well watered and fed if they showed signs of nutrient deficiency.

Each week for six weeks the plants were assessed and given a damage score based on visual assessment, and the number of damaged leaves counted. At the end of this period the lettuces were harvested and the damage assessed in detail using a Leaf Area Meter which measured the area of damaged and undamaged leaf. Finally, the leaves were dried so dry mass could be recorded as a measure of yield. 

Aims

By testing a range of barriers in both pots and on the ground, this study contributed significantly to the literature surrounding gastropod control and enabled the RHS to update the advice it gives to home gardeners regarding which products and substances are effective.

Benefits to gardeners

This experiment started to provide evidence about which gastropod barriers are effective in domestic gardens. The RHS was also able to update the advice given on its website and through the Garden Advice service for members.  

Summary of results

The results of this experiment will be published in a scientific paper and articles will be written for The Garden and other gardening press. We will use our new knowledge to update the advice we provide to gardeners.

Further information

Advice on slugs
Advice on snails
Integrated Gastropod management – another project in this topic of research