Each of the control measures outlined below, if applied only by themselves are unlikely to provide optimum control. An integrated approach needs to be considered to protect crops from damage by slugs and/or snails.
The key to effective control is monitoring:
Monitoring regularly, means pests can be detected early, ideally before seeding as there are more control options available at this time. Once the crop has been seeded and germination is commencing, control options are limited to baiting. At this time crops should be examined at night for slug and snail activity.
It is best to look for slugs and snails on moist, warm and still nights. Fresh trails of white and clear slime (mucus) visible in the morning also indicate the presence of slugs or snails. However, prior to and after applying control measures, it is necessary to estimate how many slugs and snails are present.
It is a good idea to monitor in:
- January/February to assess stubble management options for slug and snail management
- March/April to assess options for burning and/or baiting
- May to August to assess options for baiting especially along fencelines
- For snails 3-4 weeks before harvest to assess risk of snail contamination of grain and if required, implement options to minimise the risk.
How to find slugs
A useful method to detect areas infested with slugs, prior to seeding or crop emergence, is to lay lines of slug pellets with a rabbit baiter. In infested areas, slugs are attracted to the freshly turned soil and pellets placed in the furrow. Very large numbers can be found dead or dying in the furrows or nearby. On sloping ground, furrows should be run along contours to reduce the risk of soil erosion in the event of heavy rain.
An alternative method to gain an indication of the numbers of slugs present in a paddock is to place wet carpet squares, hessian sacks or tiles on the soil surface. They should at least be 32x32cm (10% of a square metre). Place pellets under them. After a few days, count the number of slugs under and around each square. Multiplying by 10 will give an estimate of slugs per square metre (/m2), at least 1-2 slugs/m2 will cause damage to canola. The table below gives an indication of thresholds.
How to find snails
Snails are usually found on stumps, fencelines and under stubbles. A good way to determine snail numbers on open ground is to use a 32x32cm square quadrant and count all of the live snails in it. This is an area of 10% of a square metre so multiplying by 10 will give an estimate of snails/m2.
Consider control options if slug and snail numbers are above thresholds
|Black keeled slug||1-2/m2||1-2/m2||1-2/m2||5/m2|
|Small pointed snail||20/m2||40/m2||5 per seedling||100/m2|
|White Italian snail||5/m2||20/m2||5/m2||80/m2|
Please note: the above thresholds are from limited data. It is essential to carefully monitor crops as distributions of snails and slugs are patchy.