Timing is everything: when to bait snails
Now is the ideal time to bait snails before most egg-laying occurs. Most snail baiting should occur between March and June. Within that range, seasonal conditions will determine snail activity and when best to apply bait.
Latest snail research
A major GRDC-invested research program on snails, led by SARDI, in collaboration with DPIRD, University of South Australia, University of Adelaide, and farming systems groups, was recently completed. The research increased knowledge of snail biology to better inform the timing of controls, focusing on the vineyard snail (Cernuella virgata), the Italian snail (Theba pisana) and the small pointed snail (Cochlicella Barbara).
At multiple sites across SA and WA, the reproductive status of snails was monitored monthly, movement behaviour was monitored continuously using time-lapse video, and micro-climate variables were measured. Data was analysed to determine links between weather conditions and snail activity (movement, breeding) to help growers identify potential baiting opportunities. For more details, see the 2021 GRDC Advisor Updates paper Movement, breeding, baiting, and biocontrol of Mediterranean snails (Perry et al. 2021). An updated snail management manual is in preparation for launch later in 2021.
Breeding seasons
For all target species, the main breeding season extended from autumn to spring. This pattern was consistent between sites and years, although the onset or finish of reproduction varied by 1–2 months depending on local seasonal conditions. On average, breeding seasons were March to late September for vineyard snail (SA – 3 sites, WA – 1 site), late February to late July for Italian snail (SA – 1 site), and March to October sometimes extending into late November for small pointed snail (WA – 3 sites). At a given location, a small proportion of the snail population may breed somewhat earlier or later.
Video footage revealed periods of high snail movement following rainfall events in early-mid summer, however, reproductive organs remained immature and breeding did not occur at this time.
Movement
Snails typically aestivate during late spring to summer, with some intermittent movement. From late summer through autumn, the main period of interest for baiting, snails increasingly moved in response to increased relative humidity at ground level. Most movement occurred at a relative humidity of at least 90% in March (or of at least 80–85% in April and May) for round snails, or of at least 95% through March to May for small pointed snails (Perry et al. 2021). Initial increase in movement was mostly overnight, between midnight and soon after sunrise, associated with dew formation.
When to apply bait
To maximise effectiveness, snail baiting should be concentrated during early autumn before most eggs are laid. Approximately March to June is a useful guideline. Baiting at other times is less effective. Snail baits kill snails more efficiently during periods when snails are breeding (e.g. autumn, winter) than at other times (e.g. spring and summer) (Brodie et al. 2020, Perry et al. 2020). Most eggs are laid in the early part of the breeding season.
We recommend that growers commence monitoring for baiting opportunities in late summer from approximately late February onwards. To detect overnight movement and confirm that snails are feeding (in hotter months they sometimes collect moisture), growers can apply small areas of bait in snail-infested areas and check for the presence of dead snails after a few days. A sequence of several consecutive nights with forecast conditions moist enough for snail movement (see Movement subheading above) is ideal to give a reasonable level of mortality.
How to apply bait
Tips for effective baiting strategies:
- Select a bait product according to forecast conditions.
- Calibrate your bait spreader for your chosen bait product to ensure even spread.
- Avoid application before heavy rainfall or at soil surface temperatures > 35oC. Exposure to high heat can degrade metaldehyde active ingredients, although UV exposure does not, and rain can break down bran-based pellets. Store unused bait in cool, dry conditions, avoiding hot sheds.
- Pellet densities of at least 30 pellet points per m2 (up to 60 per m2 where snail densities exceed approx. 120 snails per m2) are required to ensure an adequate chance of encounter. Re-apply bait as required according to label directions.
For more information, refer to the SARDI snail and slug baiting guidelines.
Further reading
Perry KD, Brodie H, Baker GJ, Nash MA, Micic S, Muirhead K (2021). Movement, breeding, baiting and biocontrol of Mediterranean snails. Proceedings of the GRDC Advisor Updates, Adelaide, 9–10 February 2021, pp 251–255.
Brodie H, Baker GJ, Muirhead K, Perry KD (2020a). Snail management: learnings from recent studies. Proceedings of the GRDC Advisor Updates, Adelaide, 10-11 February 2020.
Perry KD, Brodie H, Fechner N, Baker GJ, Nash MA, Micic S, Muirhead K (2020b). Biology and management of snails and slugs in grains crops. Final report for GRDC (DAS00160). South Australian Research and Development Institute, December 2020.
Baker GJ, Brodie H, Nash MA, Cunningham N, Perry KD (2017). Improved management of snails and slugs. Final report for GRDC (DAS00134). South Australian Research and Development Institute, December 2017.
