Grain growers are advised to assess snail infestation levels in crops and determine the need for strategies to minimise the risk of contamination this harvest.
The South Australian Research and Development Institute (SARDI) Entomology Unit warns that snails present above cutting height in the canopy or in windrows can enter the header during harvest, potentially leading to clogging of machinery and grain quality downgrades.
SARDI entomologist Kym Perry, whose work is supported through the Grains Research and Development Corporation’s (GRDC) investment in the National Invertebrate Pest Initiative (NIPI), says while it is now too late to bait, employing a combination of strategies at harvest can considerably reduce snail contamination.
“At this time of year, the aim is to minimise the intake of snails into the header, maximise the separation of snails and grain within the header, and where necessary, clean harvested grain to minimise the number of snails eventually entering the grain sample,” Mr Perry said.
Mr Perry said there was generally a trade-off between snail removal from grain and grain losses.
“Generally, reducing snail intake is more easily achieved earlier in the harvest season when fewer snails are up in the crop canopy, moisture events may still trigger snail movement back down plants, and snails are more easily dislodged from plants with lower grain losses.”
Some suggested techniques to minimise contamination include:
- Harvesting snail-infested crops first where possible before all snails have moved into the canopy. Harvesting after a light shower that has caused snails to move out of the plant canopy can also reduce snail intake without excessive grain moisture absorption.
- Windrowing cereal crops can dislodge some round snails, however, windrows of crops that are cut green and left to dry (eg canola, pulses) can be invaded by snails.
- Dislodger bars attached to the header knock a proportion of round snails from standing crops. They are often most effective in early harvested or windrowed crops. The design should be adjusted for different crop types and conditions to maximise snail removal while minimising grain shattering. Travelling at right angles to the direction of crop lean where possible can reduce grain losses.
- Stripper fronts can significantly reduce snail intake in cereal crops relative to standard open front machines. They also allow faster harvest speeds and will smash some snails as they enter the header. Raising the cutting height is a cheaper but less effective option. Both approaches leave more standing straw but this may be removed with a second pass.
- Sieves and mesh screens should be set up correctly to maximise snail and grain separation within the header. Sheet metal (punch-hole and expanded mesh) sieves are usually more effective than louvre sieves in removing snails but have a lower cleaning throughput, therefore harvest speed may need to be reduced to avoid overloading and grain losses.
- 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. Post-harvest rolling and crushing of snails is effective for all hard grains (except canola) at the optimal moisture content. An inclined belt separator is needed to remove small conical snails from canola.
The GRDC has published a Snail Management Fact Sheet which can be viewed and downloaded via www.grdc.com.au/GRDC-FS-SnailManagement. It provides information on minimising contamination at harvest as part of a year-round approach to controlling snails.
More information on harvest techniques and integrated snail management is contained in the GRDC publication Bash 'em, Burn 'em, Bait 'em which is available for viewing and download via www.grdc.com.au/GRDC-Snails-BashBurnBait.
Further information on integrated pest management is available from the GRDC via www.grdc.com.au/pestlinks.
As a result of the increased prevalence of snails and slugs in the southern cropping region in recent years, the GRDC is further investing in a number of research and development programs which are mapping different species and looking at a range of control measures.
Caption: Snails present above cutting height in the crop canopy or in windrows can potentially lead to clogging of machinery and quality downgrades.
Kym Perry, SARDI Entomology
(08) 8303 9370
Greg Baker, SARDI Entomology
(08) 8303 9544
Sharon Watt, Porter Novelli
0409 675 100
GRDC Project Code