Calibrate before you bait

Author: Rebecca Barr | Date: 29 Apr 2015

Four spreaders in a paddock

A snail bait distribution trial on Yorke Peninsula in 2013 tested the coverage of various spreaders and found that on average coverage was two-thirds of that expected with urea. Photo: Deanna Lush

Recent rains across much of south-eastern Australia have led growers to look at controlling snails and slugs due to an increase in their activity, meaning now is the ideal time to spread bait.

South Australian Research and Development Institute entomology leader Greg Baker says that in any areas that received significant rains over the past few weeks, snails are likely to be moving, feeding and mating. 

“While recent research has shown that snails don’t necessarily begin feeding when the temperature drops at the end of summer, the recent rains in the vast majority of areas will have been sufficient for all four types of snails to likely be receptive to snail baiting from now until seeding,” he said.

Slugs are likewise on the move and threaten germinating crops. Baiting to protect seedlings from slugs whilst conditions are still warm is essential.  

Mr Baker recommends that before applying the bait, growers consider the calibration of their spreader for use with snail bait.

A GRDC-funded fast-track project on the Yorke Peninsula in South Australia demonstrated the spread width achieved with the spreaders was, on average, one-third narrower than would be expected when spreading urea.

“This means that growers may only be covering two-thirds of the area they intend to cover when baiting, if they assume the coverage is the same as urea. As research found no evidence that snails are attracted to baits, it is likely they just happen upon them, so if there are gaps in the bait coverage, there will be snails that won’t get treated,” Mr Baker said.

Different baits had different distribution patterns, with larger baits resulting in a narrower spread. 


Mr Baker says growers can perform a simple calibration to ensure adequate coverage, or use a professional calibration service.

“If a grower is performing the calibration, spreading a single pass with the intended product will suffice. The grower can then go and measure how much width the bait covers, and that’s the width that can be covered in one pass. This width might range between 10 and 35 metres, depending on the machine and the bait type,” he said.

Urea spreader settings can be adjusted to maximise their spread width. Settings such as discharge position, vane angle and tilt can be adjusted and tested until the best spread is achieved. These settings are different for each machine, and are generally listed under ‘calibration’ or ‘adjustment’ in the machine manual.


The trial found high rates of bait fragmentation, where the baits fractured into two or more pieces during spreading. The extent of fragmentation was not measured directly, but it is estimated that in some cases, up to 19 per cent of baits were broken.

“Research is still continuing into the effects of fragmented baits, but it is unlikely that these smaller fragments would contain a lethal dose, so I would recommend that when growers do their calibration run, they look for fragmentation – where instead of baits there are small crumbs – and increase the dose assuming that those baits are no longer effective. For instance, if one-fifth of baits are fragmented, ideally increase the dosage by 20 per cent. But any increase to the bait rate must not exceed the maximum permissible label rate,” Mr Baker said.  

Snail management

  • Snail baiting is one component of an overall snail management strategy. The GRDC has previously published a fact sheet providing guidelines for managing snails. The key points of the fact sheet are:
  • Snail numbers can explode in seasons with wet springs, summers and autumns.
  • There are currently no means to control juvenile snails (less than seven millimetres) after sowing as they are unlikely to find baits.
  • A rule of thumb is if snail numbers are above 20 per square metre in cereals and 5/m2 in pulses and oilseeds, be prepared to deal with grain contamination at harvest.
  • Use header modifications and grain cleaning to eliminate snail contamination of grain.
  • Snails appear to build up most rapidly in canola, field peas and beans. However, they can feed and multiply in all crops and pastures.
  • Baiting before egg laying is vital. Timing and choice of controls will depend on the season. Understand the factors that determine control effectiveness.
  • Stop baiting eight weeks before harvest to avoid bait contamination in grain.
  • Monitor snails regularly to establish numbers, types, activity and success of controls.
  • To control snails, you will need to apply a combination of treatments throughout the year.
Read the full fact sheet

More Information

Greg Baker
08 8303 9544

Read the new GRDC Snail Bait Distribution Fact Sheet

GRDC Resources

GRDC Project Code YPA00002

Region South, North