Most are familiar with the common garden snail (Contareus aspersus) and the grey field slug (Deroceras reticulatum), found in gardens and vegetable patches in southern regions of Australia and throughout New Zealand. These pests cause major damage in home gardens and intensive horticultural crops.
Less commonly known by city folk is the relatively recent invasion of Australia and New Zealand by a range of introduced slugs and snails from Mediterranean areas. These have evaded quarantine since the 1920’s and now infest large parts of the cereal zones of southern Australia, including WA, and areas throughout New Zealand. These introduced species pose an increasing threat to grain and fodder crops and to intensive horticulture.
Snails are less of a problem in tropical areas but the Oriental Snail (Bradybaena similaris) is becoming a pest for ornamental and citrus trees along the north NSW coast.
The giant African snail (Achatina fulica) may also pose a future risk in tropical areas, and is already a problem in some Pacific islands where it can reach a massive size of 300mm!
A new incursion of Green Snails (Contareus aspertus) has recently been detected around Perth and is considered to be an emerging threat.
The Common White Snail was detected in grain silos on several farms in Tasmania in 2007. The pest was introduced through feed barley imported from South Australia. Common White Snails are a List A pest under the Tasmanian Plant Quarantine Act 1997.
Snails have a hard protective external shell and can survive on all soil types. However, they thrive on calcareous or limestone soils which provide abundant calcium for shell development. This is one reason why snails are a special problem for some high value vineyard regions such as the Barossa and Coonawarra.
In summer, snails enter a dormant phase called “aestivation” to avoid desiccation (dehydration) in high soil temperatures. They will seek out cooler areas such as fence posts, crop canopy, under rubble or rocks and seal off their shells.
The following autumn, snails reactivate after rain and as temperatures decline, then quickly start to forage. Different types of snails have different activation triggers. The common garden snail is generally more active during summer than other species, possibly due to artifi cial watering or irrigation of gardens and horticultural crops.
As all snails are hermaphroditic they can fertilise and lay up to 1000 eggs per season per individual. Snail populations can rise rapidly with a series of wet seasons.
Snails move at a “snail’s pace” which can be hundreds of metres in a few weeks. Re-infestations of crops from surrounding land or other crops can occur.
Snail densities can reach thousands of snails per square metre of crop.
Controlling snail populations is critical for profitable grain and fodder production.
Snails contaminate harvested crops, block header equipment, cause devaluation of grain and can clog irrigation systems. Direct damage to crops at emergence and at later vegetative stages can also occur. Young and high nutrition parts of plants such as buds, new leaves and pods are especially vulnerable, so crops can be destroyed during critical growth phases.
The Grains industry in conjunction with the SA R&D Institute (SARDI) have published good extension materials for snail control by a variety of techniques. They have promoted a three phase policy of “Bash’m – Burn’m – Bait’m”. Since snails are on stubble stems before reactivation or on the soil surface after reactivation, it is possible to bash snail shells by dragging rollers or heavy bars or cables across fallow areas, or to burn snails with stubble. These techniques are cheap and do assist, but once a crop is emerging the physical techniques cannot be used, and only baiting provides adequate snail control. Even then, it is best to apply snail bait before snails climb into the crop canopy to feed. Baiting is most effective when the snails are foraging on the ground during the months after Autumn rains. This period is also a risky time for emerging crops so it makes sense to bait in Autumn and Winter.
Techniques to minimise contamination of harvested grain include careful harvester screen selection. Cleaning the equipment helps to minimise the further spread of snails. However, “prevention is better than cure”, so early baiting to remove the pests remains a vital tool for snail management.
Animal Control Technologies (Australia) Pty Ltd
46-50 Freight Drive
Somerton, Victoria, 3062
Telephone +61 3 9308 9688
Fax +61 3 9308 9622