Snail (and slug) control – key strategies and where to next

Take home messages

• Timing and persistence are the keys to managing snails effectively.
• Seasonal weather contributed to high snail and slug populations in 2022/2023.
• Control summer weeds and bait early in autumn.
• The ‘Nail the Snails’ management guide is now available.
• Research is developing new tools for snail monitoring and management.

Background

Managing Mediterranean pest snails remains a difficult and costly task for growers in snail-affected areas. In the Southeast region, the small pointed snail, Cochlicella barbara, is prevalent. This snail has a particular preference for hiding in refuges.

No ‘silver bullet’ control method for snails has yet been identified. Integrated snail management, coupled with good timing and persistence, is the key to effective snail control. These strategies suppress round snails effectively, but conical snails can be more difficult to manage.

Investment bodies and researchers are aware of these challenges. New GRDC and SAGIT investments, led by SARDI working together with a range of research partners, are working towards finding new technological solutions for snail monitoring and management.

This paper briefly highlights key control strategies and current research working to improve snail management. Management tips for slugs, which were also problematic in 2023, are also discussed.

Why were snail numbers high in spring and summer 2022/2023

Many growers faced higher than usual snail numbers during the harvest of 2022/2023. The factors that drive higher snail populations in some years are not well understood, making prediction difficult. However, weather plays a central role.

Late winter and spring 2022 were wetter than average in many coastal regions of SA, with rainfall deciles above eight recorded all months from August to November (Figure 1). Snails start breeding in autumn and typically lay most eggs by early winter. It is likely that the wet spring allowed breeding to continue longer than usual, and/or increased the survival and growth rates of juvenile snails. Slugs also benefitted from these weather patterns (see below).

Figure 1. Monthlyrainfall deciles during winter and spring 2022. (Source: adapted from the Australian Bureau of Meteorology.

Management tips for snails

Getting the basics right is important. The key integrated management strategies for snails are:

• practice farm hygiene to prevent snails spreading to new areas (on infested harvesters, vehicles, or fodder)
• control summer weeds to remove snail refuges
• use physical controls to kill snails in summer (chaining, cabling, rolling)
• bait early in autumn before snails lay eggs
• burn stubble if needed
• clean infested grain with screen cleaners and snail crushing rollers.

These strategies all work together to suppress snail populations and are explained in detail in the ‘Nail the Snails’ guide (see below). Chaining, cabling and rolling are generally more effective on round snails than conical snails.

To improve snail suppression in the Southeast region, key points emphasised here are:

• control summer weeds early
• bait effectively (timing, rates, and application) using the tips below
• manage snails in both pasture and cropping phases.

Control summer weeds

Green weedy refuges keep snails hydrated and healthy over summer, increasing the problem in subsequent crops (Figure 2). Controlling summer weeds can reduce the over-summer survival of snails by 50% or more. Weeds should also be controlled before any other control operations (such as cabling, chaining, or burning).

Figure 2. Lincoln weed, horehound, onion weed, and any other green weeds, harbour many thousands of snails in summer (photos: Kym Perry).

Bait snails before they breed

Baiting is an essential part of integrated snail management. Baiting should occur in early autumn to kill snails before they breed. Use the following tips for effective baiting.

Apply bait at the right time

Apply bait around early autumn, as soon as snails commence moving and feeding, at the end of their summer dormancy. Snail movement is greatest when relative humidity exceeds 90% (often overnight). If both conical and round snails are present, consider baiting again around sowing time to target later-emerging conical snails. Baiting after early winter is less efficient. Cease baiting at least two months prior to harvest. There is nil tolerance of bait contamination of grain.

Apply and re-apply bait to achieve enough bait points

Always applyyour selected bait product according to product label directions. Pellet densities above 30 per m2 maximise the chance of snails encountering pellets. Consider the pellet density (per m2) when applied at the label rate (kg/ha) – refer to the product selection guide in the ‘Nail the Snails’ guide (page 26). Re-apply the bait product as required to kill snails. Re-application may be needed in areas of higher snail density, such as fence lines.

Broadcast pellets evenly using a calibrated spreader

Uneven spread can drastically reduce bait performance. Calibrate your spreader for your selected bait product and drive at pass widths no wider than the effective spread width.

Bait mice before baiting snails

Baiting mice first avoids mice consuming snail bait.

‘Nail the snails’ management guide now available

A new snail management guide is now available: ‘Nail the snails: A practical guide to integrated snail control for Australian grain growers’(see Useful resources). This is the second edition of the ‘Bash 'Em Burn 'Em Bait 'Em’ snail management manual.

Snail research news

There are two projects currently focused on improving snail management.

• ‘More effective control of pest snails in Australian grain crops’ is a 4-year (2022–2026) GRDC-invested project led by SARDI, and working together with University of Adelaide, University of South Australia, CSIRO, DPIRD, Data Effects and Molluskit. The project is investigating new technology for snail monitoring and management, such as automated stations for monitoring snail movement, ground-based AI vision for counting snails, electrostatic separation of snails and grain, biocontrol, and snail attractants and barriers. Listen to the ‘Nail the Snails podcast’ for more information (see Useful resources).
• ‘Revegetation for enhanced biocontrol of pest conical snails’ is a 3-year (2022–2025) project led by SARDI with investment from SAGIT, GRDC and Viterra, working together with Grains Producers SA and Trees for Life. The project is setting up long term research and demonstration sites on Yorke Peninsula, with border plantings of native plants, to investigate whether providing flowers in spring and summer can boost parasitism rates of conical snails by the parasitoid fly, Sarcophaga villeneuveana. In 2021/2022, SARDI performed releases of the fly on western Eyre Peninsula to establish local populations that can attack pest conical snails.

Slug management tips

High populations of pest slugs were observed in many parts of South Australia in 2023. Slugs are generally more prevalent in higher rainfall regions (>500mm per annum) and seasons. Slugs also benefitted from the wet spring conditions in 2022 (Figure 1). It is likely these conditions prolonged slug breeding into spring, and/or increased slug survival. However, the ability to predict high slug numbers in advance is presently limited.

Canola is most susceptible to slug damage. Slug problems often recur in the same paddock areas. Slug activity can be monitored directly at night, or by using rows of around 10–20 slug mats (or roof tiles) placed 10m apart, or by using bait ‘lines’ (baits placed concentrated along a seeding row and checked for dead slugs after a few days).

Integrated slug management is based on:

• weed control to remove refuges
• rolling to compact the seed bed and restrict slug movement
• tillage to a fine tilth
• rapid plant establishment (for example, hybrid seed varieties, early sowing, rolling)
• baiting at or immediately after sowing to protect seedlings.

Acknowledgements

The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC. The author would like to thank them for their continued support. The author also thanks SAGIT and Viterra.

Useful resources

Nailthe Snails: A practical guide to integrated snail control for Australian grain growers.

GRDC Podcast: Nail the Snails – with Kym Perry

Slugs and Snails

Contact details

Kym Perry
SARDI Entomology Unit
08 8429 0738
0421 788 357
kym.perry@sa.gov.au