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Sustainable Use of Grassland Herbicides

Eimear Connery ASSAP Advisor Cork East

It is essential for all users (farmers, contractors & amenity users) to take great care and follow best practice procedures when using pesticides, in particular applying grassland herbicides.

Herbicides and water quality

Monitoring of drinking water in Ireland continues to detect exceedances above the standard (0.1mg/L) for certain herbicides. In 2019, there were 82 exceedances above the limit in 27 drinking water supplies. Although, the trends in the annual results are positive and clearly show a reduction in exceedances and supplies affected, the efforts by all stakeholders must continue.

EPA update on exceedances in drinking water supplies:

The chemicals causing the greatest problems are MCPA (eg Agritox, Agroxone 50, M50, Mortone, NU46 etc) and 2, 4-D (eg Bandock EW, D50, Mortox 50 etc). These compounds known as Phenoxy Acids are highly soluble in water, more persistent in the environment and widely used. Two other herbicides with high usage and causing increasing concern are Fluroxyphyr (eg Galaxy, Hurler, Dockstar Pro) and Glyphosate (eg Roundup, Gallup etc). These four grassland herbicides accounted for over 84% of the exceedances in 2019.

Locally, Cork Co. Co. recently notified Irish Water of Pesticide failures in the Glanmire Public Water Supply (result = Mecoprop (MCPP, 2,4-D and Fluroxypyr) from a regulatory audit sample collected on 12/05/2020.

Prior to this, Cork Co.Co. have also recorded the following exceedances on this supply:

  • Fluroxypyr taken from a sample on 05/06/19.
  • MCPA, 2,4-D and Fluroxypyr from a sample collected on 14/05/2019.
  • MCPA and 2,4-D from a sample collected on 12/06/2018.

What should farmers do to minimise the impact on water bodies?

Herbicides can contaminate surface or ground water by point sources or diffuse sources. Point sources are losses in the farmyard: leaks from storage and spills from handling (mixing, filling and washing). Diffuse sources are losses in the field due to spray drift, surface runoff and drainage.

Implementing best management practice at the risky stages of handling and using herbicides is the best mitigation advice to deal with the issue:

  • The applicator must be a trained Professional Pesticide User.
  • Application equipment must be well maintained, regularly calibrated and tested every 3 years. Weed lickers and smaller boom sprayers (<3m) will be included in the testing regulation by end of 2020.
  • Discuss with your Agricultural Adviser alternative methods of control: topping, drainage, sward improvement etc. A planned control strategy can justify spraying if other options have been explored first. These are important principles of Integrated Pest Management (IPM), a key requirement of the Sustainable Use Directive (SUD).
  • Use appropriate Personal Protective Equipment (PPE) - Check safety data sheet.
  • Minimise transport risks from retailer to farm and from farm to field as accidents can happen.
  • Always read and follow label instructions (correct use, correct rate, correct time).
  • Always use the approved application method (eg MCPA is not licensed for use in a weed licker/wiper or knapsack).
  • Choose the lowest risk strategy where water bodies are a risk: eg weed licking rushes with Glyphosate or reducing the volume of chemical by spot spraying.
  • Take care to avoid spills, especially when handling the concentrated product. It is best to have a containment system in place to catch spills eg drip tray.
  • NEVER fill the sprayer directly from a watercourse.
  • Sprayers should be filled where losses to water bodies cannot occur.
  • Be aware of the location of water bodies on the farm. Take note of the buffer zone for the chemical and comply with the specified unsprayed strip (distance on label: generally 1-5m)

  • Comply with the Safeguard Zones for the protection of drinking water abstractions from ground water.
  • Spray when conditions are suitable: on a calm day, vegetation dry, no heavy rainfall for >2 days, land reasonably dry (no tyre marks) and a young crop of healthy weeds.
  • Do not apply on waterlogged or poorly draining soils that slope steeply towards a water body or any other vulnerable area leading directly to surface or ground water (eg karst). Another potential high risk pathway is field drains filled towards the surface with stone. In this scenario avoid band spraying within 5m of the drain. Spot spraying is a safer option.
  • Triple rinse the container and add the rinsate to the sprayer.
  • Spray the tank washings (internal rinsing) and clean down the external parts of the sprayer in the field. Don’t discard sprayer washings on a yard or gravel area as it can potentially enter a water body.