Snail contamination

With harvest underway, growers should be taking steps to minimise snail contamination of grain

In regions and paddocks infested with snails, 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. A series of wet winters and moist summers have resulted in snail numbers increasing in many regions of Victoria and NSW. Harvester modifications and grain cleaning will help to ensure grain is successfully delivered, but these usually incur some grain wastage. Identifying snail species and monitoring numbers before harvest, and before and after control operations is essential.

Snail management at harvest involves: (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 include:

• Harvesting snail infested crops first, particularly after a rain/moisture event.

• Windrowing cereal crops will dislodge some round snails (but watch for re-invasion of green-cut windrows left to dry).

• ‘Dislodger bars’ attached to the header knock a proportion of round snails are most effective in early harvested or windrowed crops.

• Stripper fronts can significantly reduce snail intake in cereal crops, or alternatively raise the cutting height.

• Sieves and mesh screens should be 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.

Summer management is a key part of a year round approach to effectively manage snail populations. Control summer weeds to remove refuges before undertaking other cultural control methods. Bashing stubble on hot days (> 35•C) will dehydrate and kill some snails. Burning in autumn can achieve high snail mortality but this should be balanced against the risk of erosion. Burning only chaff rows reduces the risk of erosion and snails are attracted to moisture under these windrows. Instead of spreading chaff and straw at harvest, consider burning these once autumn conditions allow. Baiting before egg lay in late summer/early autumn is critical.

For further information refer to GRDC publications: Snail management FactSheet or Bash 'em, Burn 'em, Bait 'em

 

Acknowledgements

We thank the SARDI team, particularly Bill Kimber, for earlier drafts of this article.