Recent rain has triggered snail activity in the West Wimmera and slug activity in Victoria’s south west. ConseÂquently, paddocks need to be monitored and plans to bait affected paddocks need to be put into place now.
Slugs and snails are major pests that can cause damage to emerging and establishing broadacre crops and snails can also create probÂlems at harvest, clogging machinery and contaminating grain.
Year-round slug and snail management should involve an integrated approach of various cultural, mechanical and chemical controls. However, as slugs and snails commonly become active after autumn showers (and snail mating begins soon after) the time to act is now.
Achieving the best results from snail and slug baits involves planning, monitoring and persistence. Following the steps below will help improve the success of your slug and snail baiting program.
- Monitor. The best time to check paddocks for slugs and snails is in the early morning or evening when conditions are cooler and they are more active. At this time of year round snails are commonly found on stubble, vegetation and fence posts, while pointed snails are often found on the ground in cool, shady places. Snails and slugs thrive where there are summer weeds as they provide shelter, moisture and food. This is just another reason to control summer weeds.
- Identify. Use the resources below (and there are more online) to establish the species of slug (grey field or black keeled) or snail (round or conical) as thresholds and the type and rate of bait to use will vary accordingly.Â
- Trap and count. Establish the level of infestation. To determine slug numbers set refuge traps (at least nine), such as terracotta tiles, flower-pot bases or carpet squares in a ‘W’ shape in each paddock. This will not provide an absolute assessment of slug density but will give an indication. To establish snail populations sample 10cm by 10cm quadrats at 50 locations across the paddock. Take samÂples from the perimeter to the interior of the paddock and note the density in different areas. Use simple sieve boxes to separate snails by size, as those larger than 7mm are more likely to take bait.
- Know the thresholds. In emerging cereal crops, populations of round snails greater than 7mm diameter that exceed 20/m2 should be baited while the threshold for pulses and oilseeds is 5/m2. Baiting thresholds for small pointed snails are higher; 40/m2 for cereals and 20/m2 for oilseeds. For slugs (in emerging and establishing canola crops), a population of one per square metre is considered significant and an infestation of eight slugs per square metre is considered severe (Sabeeney 2013).
- Prioritise. For snails prioritise paddocks that contain canola stubbles and then cereal stubbles. Focus on fence lines and other high traffic areas (such as around fence posts). When controlling slugs, prioritise paddocks that have a history of slug damage and where susceptible crops such as canola have been sown.
- Select a product. There are a range of slug and snail baits available commercially. They are retailed under different brand names but contain one of three active ingredients: metaldehyde, methiocarb and Fe-EDTA (iron chelate). No significant differences in morÂtality have been observed between the three active ingredients. Choice comes down to which products are registered in your state and price. A table comparing products can be accessed . The success of baiting can be influenced by timing, the species and age of slugs and snails, environmental conditions and the properties of the bait used. Bait size is important. More baits per hectare, rather than higher concentrations of active ingredient, have been shown to result in better kill rates for both slugs and snails. Timing is also important with slugs responding best when baiting occurs PSPE and snail baits most effective when applied soon after rain and before egg laying (now). Follow label directions and ensure good even spreading.
- Monitor again. After baiting check snail and slug numbers again to determine the success of baiting. Multiple bait applications may be required during winter.
- Year-round control. For the best results implement a combination of chemical and non-chemical control measures such as controlled burns, stubble bashing (snails only) and rolling.
For more information on slug and snail control consult your agronomist. The resources below might also be helpful when managing slugs and snails on your farm.
Resources
Slug control fact sheet, GRDC, https://www.grdc.com.au/Resources/Factsheets/2013/03/Slug-control-identificaÂtion-and-management.
Snail management fact sheet, GRDC, https://www.grdc.com.au/~/media/4492614E5B6B4540B4E01A43AAD97889.pdf.
Snail management, SARDI, https://www.sardi.sa.gov.au/pestsdiseases/pests/crop_pasture_pests/snail_management.
‘Seeking snail solutions: assessing snail baits and novel snail management approaches’, 2012 BCG Season Research Results.