Preventing snail contamination at harvest

Snails can settle on maturing stubble and create a major grain contaminant. Here’s how best to avoid contamination at harvest.

White Italian snails settle on maturing stubble and can create a major grain contaminant (Source: SARDI).

 

Grain contamination

Contamination issues can occur in grain when the snails accumulate in the canopy above cutting height (or in windrows). This can lead to clogging of machinery and/or quality downgrades. Harvester modifications and grain cleaning will help to ensure grain is successfully delivered, but these usually incur grain wastage. Identifying snail species and monitoring numbers before harvest, and before and after control operations is essential.

Snail management at harvest should focus on (i) minimising the intake of snails into the header, (ii) maximising the separation of snails and grain within the header, and (iii) cleaning harvested grain. 

There is usually a trade-off between snail removal from grain and grain wastage. Reducing snail intake is more achievable early in the harvest season as fewer snails will have moved into the crop canopy. This movement is dependent on rainfall events that will trigger snail movement down the canopy. Snails are more easily dislodged from plants when they have not “fixed” themselves higher in the canopy.

Harvest techniques that can will minimise snail contamination issues include:

• Harvesting snail infested crops first, particularly after a rain/moisture event
• Windrowing cereal crops, which has been shown to dislodge round snails (but watch for re-invasion of green-cut windrows left to dry)
• Attaching ‘Dislodger bars’ to the header in order to knock a proportion of round snails from cereal plants. This is most effective in early harvested or windrowed crops
• The use of stripper fronts and/or raising the cutting height, which significantly reduces snail intake
• Ensure sieves and mesh screens are set up correctly to maximise snail and grain separation within the header
• Post harvest grain cleaning is the last opportunity for snail removal. A combination of systems is usually required to meet receival standards without excessive grain losses 

Managing snails into summer

When considering summer snail control, the decision to use cabling, rolling and windrow burning should be weighed against whether it is desirable to retain stubble. If burning snails is the chosen strategy, windrows should be set up at harvest. Retained moisture in windrows will attract snails over summer and the snails can be then burned with windrows when safe to do so. This strategy is effective for the main snail species, but less so for the small pointed snail (Prietocella barbara).

Summer weed control should be carried out after creating windrows to remove alternative habitats where snails can seek refuge and source moisture during the dry months. With the removal of weeds, the snails will be forced to remain in stubble and/or windrows where cabling, rolling or burning can be utilised.

Success with cabling or rolling in summer depends upon high temperature. Choose a day where air temperatures reach 35-40°C (ground temperature about 55°C); at these temperatures snails knocked to the ground will dehydrate and die. Take care to avoid causing fire when cabling.

Recent research has shown that snails can become surface active after summer rainfall, but do not always actively feed at this time. They typically start laying eggs in autumn once the soil is moist, the timing of which varies between seasons. When required, baiting should occur before snails lay eggs, and is generally thought to be more effective in March. After a decent rain event a sample bait can be applied to determine if snails are feeding. Information gathered from this can assist in determining the necessity to apply bait across the entire paddock.

For further information on control methods refer to GRDC publications: Snail Management Fact Sheet or Bash 'em, Burn 'em, Bait 'em. 

For further information on individual snail species, refer to pointed snail, small pointed snail, vineyard snail or white Italian snail PestNotes.