Stewardship: the importance of using OSR herbicides responsibly


As the pressure grows on water companies to tackle the issue of herbicides in drinking water, key active substances such as metazachlor, carbetamide, propyzamide and quinmerac are coming under increasing scrutiny. Put simply, unless more is done to prevent these products from entering waterways, tightening regulatory restrictions will force farmers to face a future with fewer active ingredients and a significantly reduced crop protection arsenal.


As the key pre- and early post-emergence weed control active in oilseed rape (approximately 65% of the UK’s oilseed rape crop area receives a herbicide containing metazachlor), metazachlor is of particular importance in many arable rotations: especially as oilseed rape provides an opportunity to manage problem grass weeds as part of an integrated rotation and herbicide regime. However, metazachlor, plus other oilseed rape actives , have been reaching surface water that is abstracted for drinking water.  As such, the use of these chemicals is under close scrutiny, with the Water Framework Directive requiring a reduction in contamination at source rather than increasing reliance on water treatment


For now, the guidelines set out within DEFRA’s mandate to reduce pesticides are entirely voluntary. But whilst DEFRA and the Drinking Water Inspectorate (DWI) understand growers’ needs for a full and effective range of pesticides, they have not ruled out the regulatory approach. The reality is that pesticides are still finding their way into water: more therefore needs to be done if we are to limit further product restrictions being enforced.


For that reason, Adama is working with BASF, the CPA (Crop Protection Association) plus a number of water companies, to raise awareness of the issue through the Metazachlor Matters initiative. First launched in 2014, Metazachlor Matters aims to provide simple stewardship advice to prevent the loss of this key weed control active as a result of surface runoff and leaching.  In 2017, the initiative is expanded to include quinmerac when applied to oilseed rape. These guidelines are based on agronomic best practice and changing on-farm practices to maintain the long-term availability of metazachlor and quinmerac.


Herbicides such as metazachlor and quinmerac can get into water via two main sources:

  1. Spillages occurring in the farm yard during the handling, mixing and cleaning down processes: these sources can be significant but can easily be avoided by adopting good operator practice
  2. Field sources such as surface run-off or via field drainage. Avoiding pollution via field sources represent a far greater challenge but can be minimised by ‘thinking agronomically’.

‘Thinking agronomically’ means aiming to establish the crop early (ideally by the first week of September) and applying metazachlor and quinmerac early to oilseed rape: this is particularly important on drained soils where the risk of pollution increases with the onset of autumnal weather conditions (heavier, more consistent and more regular rainfall).


The guidance for autumn applications of metazachlor is therefore as follows:

  1. Early establishment is key
  2. Dose:
    • Maximum 750g metazachlor/ha
    • Reducing the amount of active ingredient applied, reduces the risk of movement to water
  3. Timing:
    • Where there are no field drains, there are no timing restrictions
    • Where fields are drained, including temporary drains, aim for an application date of 1st October, with a final cut off of 15th October. Applications after the 1st October can be made as long as soil and seedbed conditions are good and drains are not flowing (use Adama’s WaterAware app to determine whether or not it is safe to apply)
    • For drained fields in Drinking Water Safeguard Zones, apply metazachlor no later than 1st October: click here to establish if you have fields in a higher risk area.

The same guidance on timing applies to quinmerac when applied to oilseed rape.


NB: These guidelines should be applied to all oilseed rape products containing metazachlor and quinmerac, not just those supplied by Adama or BASF.


More information

For more information about the Metazachlor Matter initiative and to see the latest recommendations in full, visit the Voluntary Initiative website by clicking here .

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