Snail Management August 2015
Background:
Snails were introduced into Australia in ballast and dunnage in sailing vessels. Snails
have made their way from Coastal Ports along roads or railway lines and have also
been transported direct to farm and from farm to farm via goods, produce and
movement of machinery and vehicles. Occasionally snails have been spread by
flood waters. Snails are now a significant pest in many areas in Southern Australia;
especially in areas where calcium is freely available. Improved farming systems that
increase organic matter, improve soil moisture, reduce soil disturbance and soil
temperatures have assisted with increasing snail numbers.
Summary:
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The best snail managers have a strong understanding of snail behavior. Numbers
present, when snails are moving and location of areas where there are high snail
populations.
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Snail control is an integrated part of their farming system.
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Relative Humidity is the most important factor for snail activity; snails will move in the
summer autumn period when relative humidity is above 90%. Once snails reach
mating fitness they will move at 80% relative humidity.
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It is easier to assess snail numbers when snails are active. That is when relative
humidity is high (dew on the ground- early in the morning, or during showers)
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Check paddock borders for snails late winter so you can develop harvest strategies
to reduce risk of contaminated grain. Identify paddocks and paddock areas where
snails are high. Do not apply snail bait less than 60 days prior to harvest
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Try to harvest snail infested areas when as many snails as possible are below the
cutting height
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Stripper fronts are the most effective way of reducing snail intake into the harvester,
when there is sufficient crop bulk to prevent front losses
Snail Movement During Harvest
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Snails tend to be towards the top of cereal plants around flowering time
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Snails will move down to the ground during harvest, with showers or high humidity
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Snails will move up to the crop head with increased temperatures above thirty five
degrees
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Snails will stay on and around green plants during harvest and the summer period
Grain Cleaning Options
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The snail crusher grain roller is the most effective and efficient way to ensure snail
free grain. It can be used with most grain types be ensuring the gap between the
rollers is adjust to minimize grain damage. Twenty & forty tonne per hour units are
available.
Snail Control Options Post Harvest
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Spray out green weeds as soon as possible to reduce survival of snails over the
summer autumn period
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If there is sufficient plant bulk and soil cover, a second pass of the harvester with
minimal rotor opening in January or February during hot conditions when snails up
and stubbles are brittle, will significantly increase snail mortality over the summer
autumn period
Tips to Improve Snail Control
We currently have a high dependence on bait to control snails.
The main factors farmers should consider to improving bait performance are;
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Timing of application. Snails are active at 90% Relative Humidity in the Summer /
Autumn Period. Snails are active when there is enough dew or rain to change the
colour of the soil surface. Hand spread a small area of bait to see if snails are
feeding, check bait regularly, especially after periods of high humidity.
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Ensure it is easy to find baits by browning out weeds prior to applying bait in the
February to April period
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Ensuring an even bait distribution across bait swath. Check the number of bait pellets
across the swath and adjust spreader settings as required. Snail bait will not throw as
wide as urea, so keep spreading widths narrower.
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Correct rate to ensure enough active by matching bait rates to the number of snails
present; for example 10 kg of meta type baits in medium snail populations. Check for
live snails six days after application and reapply bait as required. Meta type baits will
last around 14 days in in March. Metarex will last around 30 days in these conditions.
Snail control can also be improved by reducing stubble height. A second past of the
harvester is the most effective method in cereal stubble, as it mulches the stubble without
increasing the amount of horizontal straw. Snails tend to use horizontal straw as a roadway,
keeping snails off the soil surface and bait.
Rolling Canola stubble before applying bait will increase snail movement and snail mortality.
This especially important when baiting Conical snails in Canola stubble. Keep in mind when
controlling Conical snails, many of them may become active later than round snails, ensuring
the need for a second bait application to achieve good mortality.
Investigation of non chemical snail control options are currently underway including use of
radiation (microwaves) and superheated steam
As is investigation of biological control, both importation parasitic flies from areas where the
snails originated (CSIRO) from and the effects of soil borne pathogens such as ciliates
(University of Melbourne)
Acknowledgements
GRDC, Australian Government & the Northern & Yorke NRM Board
SARDI Entomology 08 83039537; Michael Nash, Greg Baker, Helen De Graaf
University of South Australia; Jinhai Cai