Snails & harvest: avoiding snail or chemical contamination
With harvest underway, minimising snail contamination of grain is a high priority, to maximise price at receival and protect Australian grain growers’ access to overseas markets. Chemical residue violations also pose a significant market access risk and must be avoided at all costs (see below).
Round and conical snails contaminate grain due to their habit of climbing plants and inhabiting crop canopies in spring. Growers should aim to deliver grain free of (or with minimal) snail contaminants (see strategies section below) and absolutely free of unacceptable chemical residues.
Receival standards for the 2018/2019 harvest are available from Grain Trade Australia (GTA) website at http://www.graintrade.org.au/commodity_standards. An indicative guide on receival standards is provided below (Table1). The standards apply to round and/or conical snails (live or dead). Note that excessive snail parts (e.g. crushed snails or < half shell bodies) in grain can still be classified as objectionable material.
It is critical to note there is a NIL TOLERANCE of residues of any chemical compound not approved, or used in contravention of the label/permit or chemicals detected in excess of the Maximum Residue Limit (MRL) (refer information on declaration). This applies to the ENTIRE LOAD for ANY CROP. Therefore, UNDER NO CIRCUMSTANCES should chemicals be used in contravention of conditions specified on product labels or APVMA approved permits, which includes adhering strictly to harvest withholding periods (keeping in mind that windrowing is considered harvesting for compliance with withholding periods).
Table 1: An indicative guide on receival standards for snails for the 2018/2019 harvest, adapted from receival standards for Viterra available at http://viterra.com.au/index.php/receival-standards/. Note: Although the information has been checked, SARDI makes no warranty of the accuracy of this information. Growers should not rely on this information and are advised to check receival standards directly.
Max snails 1,2
Grain sample size
Malt 1, Malt 2, F1
DR1, DR2, DR3
Canola – snails ABOVE the 3mm screen
Canola – snails BELOW the 3mm screen
Grade 1, Cleaning
1 Round and/or Conical snails (Live or Dead).
2 Tolerances refer to whole bodies, substantially whole (more than half) snail shells, irrespective of size.
Keeping snails out of grain
Minimising snail contamination involves a combination of (1) minimising snail intake into the header, (2) maximising separation within the header, and (3) post-harvest cleaning of infested grain. The following strategies are recommended:
- Know your problem (heavily infested) paddock areas, such as paddock perimeters and calcareous outcrops.
- Harvest using a stripper front where possible – this is one of the most effective snail mitigation measures.
- Harvest the most valuable crops, damage-prone crops and problem areas first. Fewer snails are generally present in crop canopies in early spring than late spring.
- Harvesting after light moisture (triggering snail movement down plants) can also reduce snail intake without excessive moisture absorption.
- If necessary, harvest and store heavily infested areas separately to avoid contaminating clean grain.
- Consider using a dislodger bar attached to the header front to knock snails down, ideally in early-harvested crops.
- Windrowing crops dislodges snails and reduces snail intake where harvest occurs soon after, to minimise snail reinvasion of windrows.
- While more difficult on newer headers, set up sieves and mesh screens to maximise snail separation within the header. If necessary, loose chains securely attached to the top of the sieve can avoid snails clogging sieves.
- Use a snail-crusher grain roller to treat contaminated grain prior to delivery. Calibrate to crush snails while minimise grain damage.
Summer snail management for integrated control
Effective snail management requires an integrated, year round approach. Summer provides a key opportunity to kill snails, when they are vulnerable to dehydration and lethal soil surface temperatures. Summer cultural controls involve agronomic trade-offs (e.g. benefits of retaining stubble) that must be considered. Potential strategies include:
- Control summer weeds, which provide moist refuges. Do this before bashing, burning. Also control weeds before baiting in late summer or autumn.
- Rolling and/or cabling knock snails onto hot soil surfaces. Most effective on hot sunny days with maximum temperatures >35oC, followed by more hot weather, but carefully managing fire risk. Sometimes less effective in coastal areas, where overnight humidity can allow rehydration, making repeat operations necessary.
- Grazing assists with flattening stubble refuges, weed control and crushing snails, anytime between spring and autumn.
- Burning in autumn kills snails, though is increasingly unpopular due to soil erosion, reduced organic matter and moisture retention. Windrow burning is one option to limit negative consequences. If burning under a permit in Fire ban season, ensure all conditions with the permit are followed and in any case follow directions of the Code of Conduct for Stubble Burning, available from the CFS website, to reduce impacts of smoke on sensitive areas including unharvested grapes.
- Finally, baiting prior to snail reproduction is critical. Although snail movement occurs following moisture in summer, current research is showing that most reproduction occurs from late March onwards. Baiting a small “test” area after rain can determine if snails are actively feeding and consuming baits. When baiting, aim to achieve at least 30 baiting points per m2 (see the SARDI snail baiting guidelines). Where registered label rates are inadequate, use repeat applications as necessary instead. Refer to the SARDI baiting guidelines. Avoid storing bait pellets in hot sheds, as hot temperatures (>35-40oC) can degrade the active ingredient.
More information on integrated snail management: