Course: Slug Control | Last Updates: 30th August 2017
When surveyed, one in five farm advisers said they felt normal practices used by growers were likely to result in metaldehyde affecting water quality. The most commonly cited reasons were spreading into field margins, filling the spreader in the wrong place and applying pellets when heavy rain was imminent.
The best way to apply pellets is to start with the main tramlines, leaving two headland bout widths around the outside of the field until last. This strategy reduces the risk of pellets being thrown from the rear of the applicator directly into adjacent watercourses.
Spills of pellets in the field should always be cleaned up.
Most pellet application takes place with a spreader mounted on the back of an ATV. Because the power supplied to the spreader is lower than that delivered by the alternator on a tractor the Metaldehyde Stewardship Group (MSG) advises a maximum spreading width of 12 metres.
Where the spreader is mounted to a farm’s sprayer or to rear of a set of Cambridge rolls then the spreading width can be extended to 16 metres (depending on quality of pellet used).
12 metres is also advisable because not all pellets are manufactured to the same standards and while the better quality brands will spread evenly to 24 metres, most manage only 16 metres.
A standard 24m spinning disc applicator throws pellets in an arc about 12m behind the machine.
Starting in with the main tramlines also ensures that slowing down, accelerating, turning on and off are all done in the field centre, so any over-application is less likely to affect nearby watercourses.
The risk of pellets being carried onto the road in mud on the ATVs wheels when leaving the field is also reduced, as all turning is on untreated parts of the field.
It is also important to establish a 10 metre no-spread zone next to any water course or field boundary, as recommended by the Metaldehyde Stewardship Group. This 10 metre buffer zone will be a legal requirement from Autumn 2018.
Such areas are commonly grassed under ELS/HLS practices. If they are not, remember slug damage on headlands is not normally of real commercial significance in cereals, particularly as the soil is likely to be more compact, so restricting slug movement and damage.
Assuming use of a standard 24m spinning disc applicator, aim to apply half-rate across a 12m bout width twice. The double overlap produces more uniform coverage.
Control is best achieved when pellets are applied to firm, well consolidated seedbeds after rolling.
Though pellets can be incorporated with seed at the time of drilling, trials suggest this method has reduced effectiveness as slugs struggle to locate the pellets.
In high risk scenarios where the threat is at elevated levels, a pre-drilling application may be beneficial, provided that the soil can be left undisturbed for a few days after application. However, pellets should not be applied more than about one week before the expected date of drilling, because slug numbers can recover rapidly if the weather is wet.
If applied before the end of August growers are able to apply more than the 210g/ha limit of active ingredient that the MSG advises between 31st August and 31st December though growers should adhere to the legal limit of 700g a.i./ha per calendar year.
Pellets should never be applied to saturated ground. If field drains are already running, or expected to start running in the next five days, don’t spread. Similarly, do not spread if further heavy rainfall is forecast, or the weather is particularly windy. If conditions are unsuitable for spraying, don’t spread slug pellets.
To determine the need for pellets take account of field risk assessments, trapping results, soil type and conditions, previous cropping, and current and forecast weather.
Aim to apply the minimum effective dose required to achieve control as early as possible in the season. Effective early control can often reduce the need for multiple follow-up treatments, saving money and reducing the overall amount of metaldehyde applied.
Before leaving the field brush the machine down. Choose a spot well away from headlands, tramlines, gateways or where there is a risk to water.
Decontamination experiments by ADAS show accumulated soil and pellets around the machine can be a significant source of metaldehyde. But simple dry brushing can remove up to 90% of such residues.
Left uncleaned the retained metaldehyde residues are sufficient to raise 60million litres of water above the 0.1parts per billion (ppb) limit.
If washing down in the yard use a dedicated handling area, as you would when cleaning a sprayer, so contaminated run-off can be retained pending treatment.
When cleaning take extreme care if using a pressure washer. The resulting highly contaminated water is likely to find its way to a yard drain, unless you are working within a bunded area with a sealed drainage system.
Similarly, don’t use an air-line as this can lead to pellets being distributed over a wide surface area. Always wear appropriate PPE clothing.
If replacing parts in the yard put down a plastic sheet to capture stray pellets that may fall from a machine, even after it has been cleaned before servicing.
In season always keep the machine under cover between work periods and be sure to clean it thoroughly before long-term storage. This applies to ATVs, cultivation equipment, seed drills and sprayers – anything with a slug pelleter attached will retain metaldehyde residues.
Waste, including coveralls, empty containers and cleanings should be stored safely. Use a licensed disposal operator and make sure they transport waste safely – it is your responsibility.
Be sure to complete a waste transfer notice. Treat pellet spills with the same respect as liquid chemical spills.
Guidelines for pellet use
- 10m no-spread zone around all watercourses, ditches and field boundaries
- Don’t pellet if heavy rain forecast or leaching and/or run-off likely
- 700g/ha max active ingredient use per calendar year; 210g/ha max between 31st August and 31st December ; adjust rate to reflect metaldehyde concentration per pellet
- Treat according to need, use trapping to establish population levels
- Fill in field, clear up spills, never leave product unattended
- Clean applicator in field away from ditch and road
- Store kit under cover; dispose of waste appropriately
- Calibrate applicator for rate and side/rear spread
- Pellets are pesticides; users must be trained; use protective clothing
Sources of contamination – Point source:
- Washed into drains from concrete yards
- Mud from vehicles falling onto road/yard
- Applicator cleaning
- Spills in yards/field
- Washing contaminated overalls
- Spreading pellets into surface water
- Spreading pellets into ditches
- Leaching through soil into field drains after heavy rain
- Surface run-off during heavy rain
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