Recent rain has triggered snail activity in the West Wimmera and slug activity in Victoria’s south west and farmers are being advised to check their paddocks 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.
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 (early autumn) round snails tend to favour resting places off the ground such as stubble, vegetation and fence posts, while pointed snails are often found on the ground in cool, shady places.
Snails and slugs also thrive where there are summer weeds as they provide shelter, moisture and food. This is just another reason to control summer weeds.
Rufuge traps, such as terracotta tiles, flowerpot bases or carpet squares are useful for ascertaining slug populations. Place refuges in a ‘W’ shape in suspect paddocks and check them in the morning. Monitoring slugs in this way 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.
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; Â 40/m2 for cereals and 20/m2 for oilseeds.
When baiting for snails prioritise paddocks that contain canola stubbles and then cereals stubble, focusing on fence lines and other high traffic areas (such as fence posts).
A population of one slug per square metre is considered significant in emerging and establishing canola crops, a and an infestation of eight slugs per square metre is considered severe (Sabeeney 2013). Â Consequently, in paddocks with a history of slug damage, it is advisable to carryout control measures even before damage is seen.
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.
Remember, 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 post sowing, pre emergence (PSPE) and snail baits most effective when applied soon after rain and before egg laying (early autumn). Follow label directions and ensure good even spreading.
Growers should check snail and slug numbers after baiting to determine the success of the product. Multiple bait applications may be required during winter. However, for the best results implement a combination of chemical and non-chemical control measures such as controlled burns, stubble bashing (snails only) and rolling should be implemented.
For more information talk to your agronomist or visit the BCG website at: www.bcg.org.au