Snails: get up close and personal
GroundCover™ Issue: 31
Farmers are being urged to get out of their utes and onto their knees in the search for snails.
"You won't get any idea of their numbers unless you actually look for them in your paddocks and along your fence lines, especially under cover such as grass or stubble," says Suzanne Charwat of the SA Research and Development Institute.
Introduced snails on the march
She says four species of introduced snail are proving to be major pests in SA and are also being found interstate. She is adamant that if farmers want to contain the spread of snails and limit their damage to emerging crops and pastures, and contamination of grain, then they have to know what they are dealing with and how many.
"We were with a south-eastern SA farmer in May who had recently sown a paddock to lucerne. His estimate from the road was that there might have been 10 to 20 common white snails per square metre but when we turned over clumps of last year's stubble, there were hundreds per square metre. He was amazed," Dr Charwat said.
"Monitoring has to become a year-round activity with the key times being before and just after stubble management, sowing, baiting and harvest. It's a guide to any change in snail populations and a trigger for baiting when snail numbers are on the rise."
Dr Charwat is part of a research team working with farmer focus groups to try to reduce snail numbers by chemical, cultural and biological control methods. The work is supported by growers and the Federal Government through the GRDC, as well as by the SA Grain Industry Trust Fund. More than $650,000 will be invested by 2002.
The team's targets are two species of white snail (common white and white Italian snail) and two species of conical snail (pointed and small pointed). Depending on the species and their preference for certain areas, they eat emerging crops and pastures, foul and clog harvesters, and contaminate grain to the point where loads are rejected and grain has to be cleaned.
Dr Charwat said snail control to date has largely centred on the use of baits and also on cultural techniques such as stubble burning and rolling, and windrowing of barley.
She says to reduce grain contamination farmers are using pusher bars at the front of their headers to knock snails from standing crops and special sieves in their harvesters to separate snails from grain.
What else can we do?
The research program will build on these control and decontamination practices but will also investigate others including the use of pesticides, the assessment of crops that snails don't like, and the development of mechanical aids.
The project team is very keen that farmers report their observations about snails — their behaviour, breeding patterns and any novel control methods. Contact Dr Charwat.
For the latest snail information get a copy of the GRDC's Back Pocket Guide Snail Identification and Control by Dennis Hopkins of the SA Research and Development Institute and consultant Trevor Dillon. Copies of the Guide are available by contacting GRDC Publications Coordinator, Maureen Cribb, on 02 6272 5525. Also available is a fact sheet on the life cycle of snails.
Secret agent fly
Limited numbers of the first biological agent for control of pointed snails should be released this summer.
The agent is a parasitic fly collected in France and tested in quarantine at the Waite Institute in SA.
Dr Suzanne Charwat said the pointed snail species has been largely confined to lower Yorke Peninsula in SA although pockets of the pest were also in other areas.
"We don't think it will have much impact on the small pointed snail species but rather be specific to the pointed snail.
"Pointed snails remain dormant over summer on the ears and stalks of cereals and this fly's habit of attacking these dormant snails is promising although it has yet to be tested in field conditions."
Dr Charwat said nematodes are also being investigated for their impact on young snails.
At a recent field day at Minlaton in SA, SABDI entomologist Dennis Hopkins points out to growers the relative densities of snails in trial plots.
Program 2.7.1 Contact: Dr Suzanne Charwat 08 8303 9670, fax 08 8303 9542