The optimal time for snail control is during a window of opportunity after snails become active and before egg laying commences in autumn.
Snails are notorious for building up in large numbers and are an increasing problem in many parts of south-eastern Australia.
They will not only feed on emerging seedlings in autumn and winter, but can present a contamination risk at harvest.
In late spring and summer, snails move onto stubble, fence posts, weeds, and other vegetation, where they enter a period of dormancy and escape the hot soil surface.
In autumn, the onset of cool, moist conditions ‘reactivates’ the snails, after which they begin to search for food.
Subsequently, within 2 weeks after the first heavy autumn rain, snails begin to mate and lay eggs. Brief showers prior to a heavy rainfall, or a series of good dews can also stimulate feeding and mating.
This means that eggs may be ready to lay as soon as the soil is moistened with a decent rain.
Snail populations can be reduced prior to breeding with strategic burning or rolling of paddocks before sowing in autumn. The efficacy of burning in controlling snails is increased by (i) achieving an even burn, (ii) desiccating summer weeds, and (iii) turning over rocks where snails could be hiding.
To maximise the benefits of burning and rolling, baiting should be used as a follow up measure to further reduce snail numbers and the potential for population growth.
Baiting should occur once snail activity begins in autumn but prior to egg laying. This is advantageous for a number of reasons.
Firstly, baits are far more effective at controlling adult snails than juveniles as there is an increased likelihood of the larger snails (> 7 mm) encountering baits.
Secondly, there is less alternative feed and less complexity to the landscape prior to sowing, which increases the chances of snails encountering baits.
Be aware that some baits are far more stable than others under adverse weather conditions, such as cold temperatures and significant rainfall.
Rainfall (> 35 mm) erodes bran-based baits rapidly and reduces efficacy, with these products sometimes requiring re-application after only 1 week in wet conditions.
Applying baits at an adequate density is essential for effective control. Aim for no less than 30 baits per square metre, in order to ensure there is enough product on the ground for all snails to encounter a bait. Where necessary, a follow-up second baiting may be applied, especially where snail density is very high.
As we approach the winter cropping season, if you are uncertain as to whether it is too dry or too early to bait, put out a few test strips or hand spread bait in a few patches and see if dead snails are present in the morning.
Special thanks to Helen Brodie (SARDI) for her contributions to this article.
This article was adapted from the following resources:
GRDC update paper: ‘New insights into slug and snail control’