New research shines a light on snail reproduction and effective baiting.
A national project led by the South Australian Research and Development Institute (SARDI) and Primary Industries and Regions South Australia (PIRSA) is reinforcing that early autumn is the optimal time to bait snails.
The research is focused on the timing of snail feeding and reproductive activity. According to SARDI principal entomologist Greg Baker, the idea is to link environmental conditions with snail activity to give growers more insight into the best time to bait.
Entomologist Kym Perry, who works alongside Greg, said the research so far has clearly shown that baiting efforts should be concentrated in autumn, as the bait seems to perform better under warmer conditions.
“That ties in very much with what the most experienced growers are doing,” Kym said. “Fortunately, the science confirms the best practice those well informed farmers have already learnt themselves.”
He said autumn also pre-empts reproduction, which was ideal. “Our research is showing that in most seasons, snail reproductive organs start maturing from late March onwards, and most reproductive activity occurs between around late April to mid-late winter.”
Greg said cameras were being used to continuously monitor snail movement, an idea originally put forward by Michael Richards from the Natural Resources Management Board. “We have cameras at 10 sites across Australia, continuously collecting footage on movement along with associated climate data,” Greg said.
“Those cameras have shown that snails can become active even in summer, when light rain events can get them moving around for short periods of time, potentially allowing for opportunistic baiting prior to the main season break.”
The current research will help predict the duration of these early periods of snail activity and the suitability of applying a bait treatment in response. “Growers shouldn’t be overly concerned about summer snail activity,” Kym said. “They are unlikely to be reproducing at that time, as prolonged periods of moisture and feeding activity over several weeks are needed to mature their reproductive organs.”
In addition to farm enterprise costs, the market access threat from snails is substantial, particularly for the acceptance of Australian wheat and barley shipments by valuable east Asian markets such as China and South Korea.
Greg, Kym and SARDI researcher Helen Brodie were part of the 2014- 2017 GRDC project ‘Improved Management of Snails and Slugs’.
The objective was to provide the Australian grains industry with refined guidelines for managing molluscs, thereby reduce associated impacts and losses.
They found that baiting efficacy can be highly variable and often poor, and depends on complex interactions between environmental conditions, snail species, activity, size and physiology.
Ambient temperatures during feeding on baits may influence the efficacy of a given rate of bait against snails. Higher efficacy was observed with increasing temperature in trials over a tested range (10-22oC), suggesting that baiting under cold conditions (e.g. winter) may be suboptimal. High temperatures can degrade metaldehyde baits, while rainfall can degrade some bait types, particularly iron chelate products.
“For good bait performance, it is important to understand that bait encounter is random and requires sufficient snail activity and bait pellets per unit area for snails to encounter a pellet,” Greg said.
“We’ve come to the conclusion that we probably need a higher number of bait points than perhaps has been traditionally accepted.
“To optimise baiting efficacy, a minimum of 30 to 60 bait pellets should be applied for snail densities up to 160 round snails per m2 or 320 pointed snails per m2. Where label rates are lower than this, growers are advised to re-monitor live snail densities after baiting and consider re-application as needed.”
Greg said it was important to be aware that mice can take baits and that all products applied for snail control in grains must be used strictly in accordance to label directions.
Changes to farming systems, including minimal tillage, increased stubble retention and standing stubble, are encouraging snail survivorship and reproduction.
“The combination of extra organic carbon in the soil, extra soil moisture at the surface, shelter and food, creates an ideal environment for snails,” Greg said.
“Applying baits after controlling weeds, reducing stubble and before crop emergence is likely to increase bait efficacy by increasing the chance that snails will encounter it.
“The study also revealed that baits do kill juvenile snails, though lower mobility of small juveniles and the presence of crop plants and stubble all reduce their chance of encountering baits.
“Also, high numbers of juveniles means that there are always lots of survivors”.
“This reinforces the need to target adults during the autumn period – before egg laying and juvenile recruitment occurs.” For more information on slug and snail baiting guidelines, head to pir.sa.gov.au