Growers urged to monitor and manage slugs and snails

The Grains Research and Development Corporation (GRDC) has invested in research into slug and snail ecology and control which suggests the move to minimum till in our farming systems has created a more favourable habitat for the persistence of these pests from season to season.

Retained stubble and improvements to soil structure as a result of minimum till practices has seen an increase in soil moisture holding capacity, soil macropores, organic matter and available calcium, which has resulted in population increases and a wider geographical spread of slugs and snails.

According to this research growers should now be considering baiting, in areas where snails and slugs have become active. Baiting is most effective when snails and slugs are actively feeding but before they start mating and egg-laying. Research has also shown that successful control requires knowledge of the snail or slug behaviour, the type, size and numbers present, and the application of cultural, biological and chemical control techniques.

South Australian Research and Development Institute (SARDI) entomology program leader, Greg Baker said moisture is the biggest determining factor for breeding, and with snails currently becoming active after summer dormancy, now is an ideal time to start baiting.

“Both snails and slugs can be controlled in no-till, full stubble systems if growers understand where and when controls are applied, and follow a few basic guidelines,” Mr Baker said.

“Snails won’t begin mating generally until moisture levels increase, and while dews or cooler temperatures at night in autumn may begin that process, eggs won’t be laid until we receive significant rainfall.

“So now it is an ideal time for baiting and by using the recommended rates of bait growers can generally drive down numbers significantly.”

Mr Baker said growers who have noticed a high density of snails should bait at the maximum label rate, and then monitor in the following days to determine the need for a follow-up bait treatment.

“To count them, growers need to get down on hands and knees and use a quadrat (eg 30cm x 30cm), and only count the live snails, which will be juicy rather than dry if squashed. It is also important to ensure the bait is being consumed by the snails not by mice. If baits are disappearing with no corresponding dead snails, this may indicate a mouse problem,” he said.

“Growers who have been experiencing dry weather are also likely to have a low weed base, which also improves baiting effectiveness so again it makes this an ideal time to be monitoring and managing the pests in the paddock. If weeds are present we advise growers control them prior to baiting.”

Baiting for snails occurs at a different time to slugs. If growers have both snails and slugs, one bait in autumn may not be good enough. Assessing the context in which growers are trying to control these pests is key as different products will suit different situations. 

GRDC research shows that baits should be considered as crop protectants, with cultural methods also required to reduce populations.

Several exotic snail and slug species of European-Mediterranean origin have now established in Australia and become significant pests of grain crops.

Snails cause substantial economic losses through yield loss from feeding damage, field control costs, additional harvest costs, grain value loss, receival rejection and threaten market access. Slugs cause major losses from feeding damage at crop establishment, resulting in increased cost for re-sowing and paddock control.

Mr Baker said the common vineyard snail and the pointed snails continue to expand across southern NSW, so hygiene measures to try and reduce further spreading are worth considering. 

“The move to no till/stubble retention/less burning and less grazing in some instances, has resulted in less disturbance, better ground habitat (moisture, shelter), more off-ground summer refuges and less bait encounter, which in turn collectively results in greater snail survival and growth and reproduction,” he said.

“To counter this growers need to do more than bait, but also look after stubble management and hygiene year round.”

Narromine grower Billy Browning said in their area overhead irrigation from the river seems to be one reason behind their increasing slug problems.

“We don’t see slugs in our flood irrigation paddocks, only the overhead which is the direction we ultimately want to move in for better water efficiency,” he said.

“Baits cost us about $54 a hectare and we ultimately feel like it is a preventative measure rather than a cure.”

Greg Baker said the role of crop rotations needs to be considered in the management of slug populations across years. For example, slug numbers can build up in canola crops.

“If growing canola sow early, ensure quick establishment by using either hybrid seed or grade open pollinated varieties (<2mm seed). Look at the use of foliar N to seedlings (GS 1.4) to ensure quick establishment in lower risk situations as a follow up after baiting at sowing," he said.

“Baits at sowing are required in high risk situations to prevent seed damage from slugs feeding in the drill row.”

“The key for effective slug baiting is to protect the crop at sowing to prevent seed and seedling damage and the best results will be achieved when slugs are active and feeding, with the timing varying depending on paddock and seasonal conditions and the species present.

A range of GRDC publications have been developed for GRDC Southern and Western Regions that can be adapted and tactics applied to the emerging slug and snail populations in the GRDC Northern Regions.

To ensure snails are likely to encounter pellets, use the appropriate rate according to the label.