Paddock Practices: Tips and tools for reducing snails at harvest

Key Points

• Snails are more active at night
• It is usually best to harvest during the day
• Consider harvester modifications
• Grain cleaning may be required.

Grain growers in Western Australia’s southern high rainfall areas are advised to consider a range of harvest practices to help reduce the risks of snails contaminating grain this season.

High snail numbers not only pose a threat to grain meeting quality standards, but can also clog-up machinery (in the case of round snails) and cause losses in subsequent crops if not controlled at this time of the year.

Tactics such as harvest timing, height of cutting, using brushes and/or crushers and grain cleaning can be effective in helping reduce the amount of snails getting into harvested grain. Followed by burning and/or windrow burning, these measures will also help to control snail numbers going into next year.

More information about year-round integrated snail control measures can be found in the comprehensive Stirlings to Coast Farmers (SCF) manual Snail Management Guide for WA Farmers.This was produced with assistance from the Council of Grain Grower Organisations (COGGO) and researchers from the Department of Primary Industries and Regional Development (DPIRD).

When to take action - how many snails are too many?

It is advised to monitor snail numbers and look for snail damage in crops three to four weeks before harvest to assess grain contamination risks from this pest.

The contamination risks will depend on snail species and size in relation to type of grain crop, and the position of snails relative to cutting height. The risks tend to be higher in lower-yielding crops.

More information about determining when snail control tactics can be beneficial at harvest can be found in the GRDC’s Snail Management Fact Sheet

Harvest timing

There are two types of snails that may be found in paddocks in the high rainfall cropping areas of WA - small pointed snails and round snails (white Italian and vineyard snails).

DPIRD research officer, Svetlana Micic, says research conducted through the Department’s Boosting Grains Research and Development project, has found one of the best measures to minimise grain contamination from these pests is to time the harvest operation when snails are low in the crop canopy and not in the grain heads.

This is typically early in the harvest period for both snail types, as they can be harder to dislodge from the crop canopy as the weather gets warmer.

Svetlana says round snails are more easily dislodged from grain, whereas small pointed snails can be found in sheltered locations (such as between the leaf and stem) and are not easily dislodged from crops by the harvester.

As temperatures increase, round snails are more likely to climb up on to crops, whereas small pointed snails are more likely to seek shelter where it is cooler (including under stubble).

Round snails are more likely to climb down from crops in cool conditions, so timing harvest to coincide with cool days, or at night, reduces the risk of contamination from these pests.

Small pointed snails are active at night and during cooler, overcast weather and are more likely to climb up the stem of a plant during these periods. In ‘hot spot’ areas for this type of snail, it is recommended to harvest during the hottest part of the day, when higher numbers of small pointed snails are found under stubble. It has also been found that these snails are easier to dislodge from crop canopies after light rainfall.

Svetlana advises that when swathing canola, small pointed snails can move into windrows (swaths) of crops, such as canola.

She suggests harvesting windrowed crops as soon as practicable, as the longer a swath is on the ground, the higher the number of small pointed snails that may be found harbouring under or in the swath (and then incidentally harvested).

Also consider swath height, as swaths that are close to or on the ground tend to have more small pointed snails in the grain, she advises.

Harvest cutting height

Using a rotary stripper in front of the header has been found to dislodge up to 50 per cent more snails than using a conventional front, especially for large snail species and in medium to heavy crops in southern WA.

When used in combination with a dislodger bar, the stripping front can remove more snails. But this system is not as effective for small pointed snails.

Research and experience has shown rotary stripping fronts are most suited to heavy-standing cereal crops of even height and on even terrain.

An alternative is to raise the cutting height of an open front machine to minimise intake of bulk crop material.

But these systems can result in more standing straw, which may impact on residue handling at the next seeding.

More information can be found here.

Header modifications

Dislodger barsGRDC advises in its ‘Snail Management’ Fact Sheet that a rigid dislodger bar, or flexible fingers about two metres in front of the knife, can reduce header intake of round snails by up to 80 per cent in cereals and 60 per cent in tall pulse crops.

Svetlana says experience has found these bars are most suited to large round snails that are located high in the canopy and are more effective when used early in the harvest period.
Key points to consider include:

• Use a machine designed to reduce snail numbers and minimise grain losses
• It is best if height is adjustable
• Set close to crop cutting height, especially for cereals
• Most effective for heavy snail infestations
• May only be needed on the paddock perimeter
• Use early in the harvest period.

Rotary brushes

An alternative to a dislodger bar is to use a rotary brush, typically made from polypropylene and with a choice of having a soft or harsh action.

Brushes tend to have about five rows of bristles, each 50 cm long and 0.2cm in diameter and about 5 cm apart, fitted to a 150mm diameter tube.

The system is fitted to the header front so that the edge of the brush is just clear of the finger reel and able to rotate forwards and backwards at an adjustable speed.

It has shown to be particularly useful for minimising grain losses in delicate crops, such as field peas, but can be harsh enough for use in cereals.

For more information go here.

Use of sieves

Svetlana says replacing adjustable louvre sieves with fixed aperture sieve designs tailored to the size of snails and grain, has been effective in removing round snails from grain at harvest in WA conditions.

Tips for using these include:

• Use sieves with specifications for the crop being harvested and snail size/species
• Punch hole screen size and shape will change with crop type and seed size
• A ‘cross-wise’ design best suits expanded metal mesh sieves
• Louvre sieves are well suited to bigger grain sizes, such as faba beans
• Reduce fan speeds.

More information can be found here.

Harvest intensity

Increasing the threshing intensity of the harvester can be another option to destroy or remove snails. It is advised to loosen grain conveyor belts when using this modification.

More information can be found in the GRDC Snail Management Fact Sheet.

Grain Drying

Svetlana says small-scale WA trials have shown drying the grain in a grain dryer will not kill snails.

She says if seed is being retained for the next season’s planting and it has snails in it, some of these snails are likely to be alive. Sowing this seed in snail-free paddocks can increase their spread. It may be necessary to clean this seed.

Cleaning contaminated grain post-harvest

Cleaning grain after harvest may help growers with heavy snail burdens to meet receival standards and this could require a combination of air separation, screening, scalping, rolling and/or crushing to separate snail material from grain.

More information about setting-up these systems on-farm can be found here.

Research in recent years by the Stirlings to Coast Farmers group, with GRDC investment, has found snail-crushing rollers can be an effective and versatile on-farm grain cleaning option to remove snails from grain of the same size.

These are typically a two-roller or a dual-roller machine that is capable of processing up to 25 and 45 tonnes of grain per hour respectively.

The SCF group found a two-roller design was best used in combination with conventional grain cleaners, as the use of the roller alone did not always achieve a grain sample that met receival standards.

Group project officer Kathi McDonald says pre-scalping and post-screening with a grain cleaner, either side of the rolling operation, were typically needed.

She says the group’s findings indicate the efficacy of a snail roller depends on the clearance between the two rollers, grain moisture levels, roller hardness, speed of rotation and feed rate of grain into the rollers.

It is important to continually monitor its effectiveness during harvest in removing snails and causing minimal damage to grain.

For cereals and pulses, results were best with the use of two sets of rollers of different hardness.

SCF imported a snail roller to WA in 2016 and is continuing to assess its performance in conjunction with DPIRD and SCF members. The group and its members are also looking at ways to improve the roller design for local conditions. More information can be found on the SCF website at: www.scfarmers.org.au

GRDC has more information and trial results for grain cleaning here and here.

Managing stubble - bashing snails post-harvest

For an integrated snail management plan, post-harvest use of stubble bashing with a cabling, rolling or slashing machine - or using livestock grazing (coupled with burning) can help to reduce populations for the next year.

Bashing aims to knock snails off stubble and on to the hot soil surface after harvest to dehydrate and kill them.

For optimal results it is advised to:

• Remove summer weeds before bashing stubble
• Consider cabling to roll stones over in stony paddocks
• Bash stubble on hot days with temperatures above 35ºC
• Try to pick a period of hot days
• Flatten all upright plant material
• Consider repeating the treatment if snail numbers remain high.

Research with GRDC investment has shown snail kill rates from post-harvest cabling, rolling or slashing tactics ranged from 50 to 90 per cent when air temperature was hotter than 35°C. This compared to about 30 per cent snail kill from grazing.

It is advised that rolling and slashing are typically only effective on round snails, as pointed snails often hide under rocks.

More information about setting up stubble management systems and the effectiveness of control can be found at GRDC’s Bash ‘Em, Burn ‘Em’ Bait ‘Em.

Stubble and windrow burning

DPIRD research with GRDC investment has identified stubble burning can also help to reduce snail populations in high rainfall areas.

But widescale burning may impact on soil health, particularly in south coastal regions, and at an estimated cost of $30/ha, it is not a cheap control option, according to Svetlana.

She has carried out trials of whole paddock burning and says this can lead to soil erosion problems, particularly on sandy soil types.

Svetlana says growers have to weigh up the risks of having an exposed paddock with the impact of the snail infestation.

When comparing effectiveness of snail control using windrow versus whole paddock burning, indications were that windrow burning showed more promise for canola stubbles.

In a harvested canola paddock, 25 times more snail numbers were found in the windrow than the inter-row, allowing them to be partially controlled by windrow burning.

Previous GRDC-funded research trials have found windrow burning in canola stubbles can reduce small pointed snail populations by more than 90 per cent.

In Svetlana’s trials, a barley stubble paddock that had been windrowed still had 50 surviving snails per square metre in the inter-rows, after the whole paddock was burnt. She attributed this to presence of green weeds in the inter-rows and says this reiterates the importance of weed control before burning.

More information about these trials can be found on the GRDC’s Online Farm Trials website.

GRDC research investments in snails

The GRDC snail and slug investment is led nationally by the South Australian Research and Development Institute (SARDI) and aims to expand ecological and biological knowledge of snails and slugs to provide growers with regionally-specific information for effective timing of controls.

In WA, the focus is the grainbelt’s two most problematic species - small pointed (conical) snails and black keeled slugs - and trial sites are in the Great Southern and south-east coastal regions.

More information

Contact

Svetlana Micic, DPIRD, 08 9892 8591, svetlana.micic@dpird.wa.gov.au
Kathi McDonald, Stirlings to Coast Farmers Project Officer, 0408 418 531, kathi.mcdonald@scfarmers.org.au

Useful resources

• Stirlings to Coast Farmers Snail Management Guide for WA farmers
• GRDC Fact Sheet Snail Management
• GRDC Bash ‘Em Bait ‘Em Burn ‘Em Integrated Snail Management hub

*Note snail research is also carried out through the DPIRD Boosting Grains Research and Development project and the SCF snail management research received assistance from COGGO.