Reducing snail contamination a priority this harvest
Author: | Date: 10 Nov 2011
Reducing snail contamination a priority this harvest
Grain growers in South Australia face a heightened risk of snails contaminating grain this harvest, resulting in potential downgrades and clogging of machinery.
The build-up of extreme snail populations during the 2011 cropping season has increased the potential for significant issues at harvest, according to authorities.
The South Australian Research and Development Institute (SARDI) Entomology Unit is urging growers to be aware of receival standards and to monitor snail populations (particularly numbers that are similar in size to grain) prior to harvest to determine the need for header modifications.
SARDI entomologist Kym Perry says in spring snails increasingly move into the crop canopy in preparation for summer aestivation.
“At harvest, snails present in the canopy above cutting height and also in windrows are readily harvested along with grain,” said Mr Perry, whose work is supported by growers and the Australian Government through the Grains Research and Development Corporation’s (GRDC) investment in the National Invertebrate Pest Initiative (NIPI).
“By harvest time, options to reduce snail contamination are limited to minimising the intake of snails into the header, maximising the separation of snails and grain within the header, and post-harvest grain cleaning.
“Strategies to reduce snail intake are generally more effective when applied early in the harvest season when fewer snails are present in the crop canopy, snails are more easily dislodged from plants with lower grain losses, and they still respond to moisture events by descending down the plant canopy to resume feeding.”
Mr Perry said a cleaner sample could be achieved by planning ahead and taking appropriate steps, such as:
Harvesting snail-infested crops first where possible. Early harvesting after a light shower (less than 2.5 millimetres) can also reduce snail intake without excessive grain moisture absorption.
Windrowing of cereal crops will dislodge some round snails and some may eventually move out of the windrows. However, windrowing of green crops (such as canola and pulses) may lead to more snails moving into windrows and eventually entering the header.
Dislodger bars will knock round snails from standing crops in front of the header and are most effective in crops being windrowed or harvested early. The design should be adjusted for different crop types and conditions to maximise snail removal while minimising grain losses. Travelling at right angles to the direction of crop lean where possible can further reduce losses.
Rotary stripping fronts on headers significantly reduce snail intake in cereal crops relative to open front machines, improve harvest speed and will also 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 and flattened straw lengths in wheel tracks which could create problems at sowing. Some growers undertake a second pass to remove standing straw; delaying this until mid summer may directly kill some snails.
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 systems take advantage of differences in physical properties (such as weight, shape, size and strength) to separate round and conical snails from grain. 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. Rolling is ideally combined with pre-scalping (sieving out larger snails first) and re-cleaning afterwards. An inclined belt separator is needed to remove small conical snails from canola.
Mr Perry said that after harvest, summer management as part of an integrated year-round approach should be a priority this year to reduce snail carryover into next season, however the benefits of cultural practices for snails need to be balanced against other agronomic factors (such as erosion risk etc).
“Controlling summer weeds initially is important to remove food and moist shelter sites. This will make other strategies more effective, including bashing of stubble on hot days (over 35C) and autumn burning.”
Mr Perry said early baiting when moisture triggers snail activity but before egg-laying commences, typically in late summer/early autumn, is critical to prevent further population build-up.
Last summer, prolonged moisture is thought to have led to a highly unusual egg-laying event in January/February producing high juvenile populations by autumn.
“If these unseasonably moist conditions recur in summer and snails are active for an extended period, then summer baiting under moist and overcast conditions (to reduce ultra violet degradation of baits) should be considered,” Mr Perry said.
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.
The GRDC also has available a Snail Identification and Control Back Pocket Guide which helps growers identify the snails that are pests of crops and pastures and outlines year-round control strategies. It is available for viewing and download via www.grdc.com.au/GRDC-BPG-Snail.
Further information on integrated pest management is available from the GRDC via www.grdc.com.au/pestlinks.
Caption: Summer management of snails, including bashing stubble on hot days, should be a priority to reduce snail carryover into next season.
• More information is available from Kym Perry at SARDI on (08) 8303 9370.
• GRDC Project Code: CSE00046
• This media release and other media products are available via www.grdc.com.au/media
GRDC Project Code CSE00046