Summer provides key opportunity for snail management
Date: 21 Dec 2012
- Baiting before egg laying is vital
- Control summer weeds which provide habitat for snails
- Bashing, rolling, slashing and cabling are other summer control methods
- Baiting after summer rains may also reduce snail numbers.
Southern region grain growers are being encouraged to activate summer snail management strategies to keep on top of snail populations.
According to the latest Snail Management Fact Sheet published by the Grains Research and Development Corporation (GRDC), controlling snails before egg-laying commences is fundamental to successful integrated control.
Historically, growers have typically commenced application of baits around the late March/early April period when the first moisture triggers snail activity. Following wetter conditions more recently, a number of grain growers and farm advisers reported successfully baiting snails during the wet summer of 2010/11 and again in early 2012 following summer rainfall events.
Researchers say the issue around whether snails can successfully breed during these very wet summers still needs clarification. Nonetheless, some growers and advisers are now considering the value of earlier baiting in summer when the opportunity presents itself as part of an overall snail management strategy.
Mallala (SA) grain grower Richard Konzag says if sufficient rainfall occurs during summer to keep the soil damp for several days, his experience shows snails will move down from posts and stubble to take the bait.
“I have seen as many as 10 to 12 dead round snails around a single bait,” said Mr Konzag, who is also a GRDC Southern Regional Panel member.
According to the GRDC Fact Sheet, one to two millimetres of rain are enough to trigger activity, but snails will only remain active as long as conditions remain moist.
Grain growers are encouraged to monitor after summer rainfall to determine whether snails are moving down from resting sites onto the soil surface. If snails do become active and moist conditions are forecast to continue, this could provide a short window for summer baiting to help to reduce snail populations.
Research is still needed to validate this approach, given the higher potential for UV degradation of the active ingredient in snail baits at this time of year which would reduce bait persistence.
South Australian Research and Development Institute (SARDI) Principal Entomologist Greg Baker, whose research is supported by the GRDC, says targeting adult snails before they mate and lay eggs is critical to minimise the next generation of snails.
Baits are widely considered to be less effective on juvenile snails (less than 7mm long), but Mr Baker says better understanding bait performance on juvenile snails is an issue that needs further attention and is one focus of a current GRDC study of comparative bait performance.
“Snails are hermaphrodites, enabling each to lay an egg cluster after mating. Round snails lay up to double the number of eggs of pointed snails,” Mr Baker said. “In the field, each round snail can lay up to 400 eggs per year. Eggs are laid in the top soil.”
Mr Baker said control of summer weeds was also an important snail management practice.
“Snails love summer weeds as they provide shelter, moisture and food through the hot months. Controlling summer weeds removes an important source of moisture and helps achieve better results with other snail control measures such as stubble management.”
In summer, round snails favour resting places off the ground (stubble, vegetation and fence posts) while pointed snails are more often found on the ground in cool, shady places.
Snail mortality after baiting is between 60 and 90 per cent for mature round snails and 50 to 70 per cent for mature pointed snails. Mr Baker said more bait points per hectare rather than higher concentrations of active ingredient had been shown to result in better kill rates.
The GRDC is conducting new research on baits with a focus on juvenile snail control, including formulation testing of alternative ingredients and biological control agents.
Previous research found no difference in kill between active ingredients.
Meanwhile, other means of snail control over summer include stubble bashing to knock the snails on to the hot soil surface to dehydrate and kill them. While rolling, slashing and cabling standing cereal or canola stubble are also effective techniques for killing snails, strategic burning (when permitted) remains the most effective method of pre-breeding snail control, provided a hot, even burn is achieved.
If summer weeds are controlled prior to burning and rocks are turned by fire harrowing or cabling, nearly 100 percent snail kill has been achieved. Agronomic experts say burning must be avoided on erosion-prone soils and should be used judiciously to minimise the loss of stubble being returned to the farming system.
The GRDC’s Snail Management Fact Sheet, which can be viewed and downloaded via www.grdc.com.au/GRDC-FS-SnailManagement, provides information on baiting after summer rainfall and other methods of control over the summer months as part of a year-round approach to controlling snails.
More information on harvest techniques and integrated snail management is contained in the GRDC publication Bash 'em, Burn 'em, Bait 'em which is available for viewing and download via www.grdc.com.au/GRDC-Snails-BashBurnBait. Further information on integrated pest management is available from the GRDC via www.grdc.com.au/pestlinks.
Caption: In summer, round snails favour resting places off the ground, such as stubble.
Greg Baker, SARDI
(08) 8303 9544 or 0427 039 544
Kym Perry, SARDI
(08) 8303 9370
Sharon Watt, Porter Novelli
GRDC Project Code CSE00046
Region South, North