Whilst baiting is only one technique for successful snail and slug management, it becomes the primary tool for reducing populations and protecting crops before sowing and at the early stages of emergence.
Snails and slugs have become an increasing problem in Australian broad acre systems as the move to conservation farming practices creates the ideal habitat for snails and slugs. Svetlana Micic DPIRD Entomologist commented ‘What’s changed is farming practice, so once upon a time we did full tillage and burning which meant numbers were quite low across the landscape but with minimum tillage and stubble retention, it means that there is a lot more soil moisture being retained over Summer.’ This has created a need for an effective control option, which is currently provided in the form of molluscicidial baits, however there are a number of highly variable options to choose from which can make it difficult to determine which option will provide the best control and return on investment in any given situation.
Most growers are aware that snails and slugs will not actively seek out baits, but rather that encounter drives consumption behaviour. As such, the number of baits per m2 provided by a product then becomes the critical characteristic in determining the provision of effective control. While bait size, which directly influences baits per m2 is critically important, there are two other very important factors to consider; namely bait toxicity and environmental durability.
Toxicity is becoming more prevalent in discussions particularly as a greater number of participants enter the baiting market. When thinking about toxicity, bait formulation and composition need to ensure the active ingredient can stand up to environmental exposure in the paddock and still offer a lethal dose over the life of the pellet. Like most things in life, you get what you pay for and cheap rarely equates to sufficient environmental stability. If a bait only contains the minimum dose of active material and then breaks down quickly in the field, it would be difficult to argue that it could possibly be deemed effective in delivering a suitable duration of available toxic encounter, which is critical for an effective broad acre baiting program. Furthermore, whilst research suggests snails and slugs will not actively seek out baits, they appear to be attracted to feeding activity, which is often seen in the field as cluster feeding. By providing a high load (50 g/kg) active in a compact, weather resistant bait, Imtrade Metakill offers the benefit of providing a greater number of victims from a single pellet via delivery of a lethal dose from a low rate of consumption.
Returning our thoughts to the terminology of duration. Duration considers the length of time a bait physically offers the elements of encounter and toxicity. The length of time a bait is able to offer a chance of lethal encounter is directly correlated to overall population efficacy and thus the value of the return on investment provided by any given product. The key Factors influencing duration are weather tolerance (how long will the bait remain in damp or high moisture environments), longevity (how long will the bait deliver a lethal dose) (Nash et al., 2016; McDonald and Micic, 2017) and consumption rate (how much of the bait is left over after an initial encounter and feeding occurrence). All of these factors point to the harder flour based, high loading (50 g/kg) baits as the preferential option over the cheaper bran-based alternatives.
Imtrade Metakill® Snail and Slug bait (100,000 pellets per kg, label rate 4-8 kg/ha) and Meterex® Snail and Slug bait (60,000 pellets per kilogram, label rate 5-8 kg/ha), both high load metaldehyde (50g/kg) long life baits, offer significant benefits over the lower concentration (15 – 30 g/kg) bran-based alternatives; as demonstrated in the GRDC snail and slug baiting Guidelines Nov 2016 (www.pir.sa.gov.au). Based on current label rates for the lower concentration, bran-based actives, most deliver well below the recommended baits per m2 rates recommended for control, and this is further compounded by their lower durability in the field, and as such, these characteristics should be given careful consideration before deciding on the best option for your situation. (GRDC Mitigating Snails, Slugs and Slaters in Southern Western Australia May 2019).