Avoid spring surprises: be proactive about snail and slug control.
Editorial written by AgNova for the Spring 2020 Seasons Magazine.
Weather conditions across southeastern Australia this year have favoured snail and slug breeding.
Therefore, it is crucial to start monitoring pest activity and apply baits this spring where needed. In 2018 and 2019, dry autumn/winter conditions across most areas limited snail and slug numbers, reducing the threat to crops. But this season is different.
As the temperature increases in the spring, so too does snail and slug activity. As farmers take advantage of moist conditions and warming soil by sowing spring/summer crops, establishment pests need to be managed. Slugs become more active and breeding is optimal between 10°C and 16°C (Schley and Bees, 2003). Proactive slug control using an all-weather bait such as Metarex® will be needed directly after sowing spring crops: for example, poppies, maize, mung beans, vegetables, summer fodder and pastures. The moist conditions allowing slugs to build up numbers during the first half of the year (Fig.1) and in some areas last spring, means an increased threat to spring crops. It is expected perennial crops, such as asparagus, will also need greater protection this season prior to spears emerging to avoid rejection.
Snail breeding is favoured by a wet autumn/winter (Baker et al., 1991; Baker and Hawke, 1990). Large numbers of juvenile snails have been observed in July, despite controls being applied in late March. The late summer rains in most areas of southeastern Australia resulted in snails mating earlier than expected, with brown garden and Italian snails laying eggs by March and hatching by April. Controls applied in April were too late, resulting in large numbers of snails being observed late winter that could contaminate crops this coming harvest.
Control prior to harvest to reduce product contamination (e.g. Italian snails moving into vine canopies late spring) and reinvasion (e.g. garden snails from sprinkler lines into celery) is needed in situations where control in autumn was not achieved. However, application timing may be compromised due to harvest withholding periods. Autumn snail baiting is recommended by the grains industry and in citrus management guidelines, with recent research indicating best results are achieved when adults are actively breeding in autumn (Brodie et al. 2020). Observations so far this season indicate snail populations prior to harvest will be dominated by juveniles, which require a higher dosage of active ingredient to kill.
Using a product such as Metarex that is attractive, has an even size pellet and is highly palatable will ensure a lethal dose is consumed, despite being applied when conditions are not as optimal as recommended. Applying small pellets in an attempt to control spring snail populations only increases the chance of delivering a sub-lethal dose. Hence, snails will recover and contaminate high value crops such as grapes, citrus, pome fruit, vegetables, cereals, canola, and pulses.
Appreciating the influence of seasonal conditions on snail and slug populations, diligently monitoring pest activity and applying a bait that works in a range of conditions will result in protecting your crop from damage and maintaining market access by eliminating contamination.
Figure 1. Australian Rainfall Deciles 1 Jan – 30 Jun 2020.
Baker, GH, Hawke, BG (1990) Life History and Population Dynamics of Theba pisana (Mollusca: Helicidae) in a Cereal-Pasture Rotation. Journal of Applied Ecology 27, 16-29.
Baker, GH, Hawke, BG, Vogelzang, BK (1991) Life history and population dynamics of Cochlicella acuta (Müller) (Gastropoda: Helicidae) in a pasture-cereal rotation. Journal of Molluscan Studies 57, 259-266.
Brodie H, Baker G, Muirhead K, Perry K (2020) Snail management – learnings from recent studies. GRDC Grains Research Update 2020, Adelaide https://grdc.com.au/__data/assets/pdf_file/0027/391914/10945-Adelaide-update-proceedings-2020-Inter.pdf
Schley, D, Bees, MA (2003) Delay dynamics of the slug Deroceras reticulatum, an agricultural pest. Ecological Modelling 162, 177-198.
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