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Oilseed rape herbicide stewardship matters

Oilseed rape filed and field boundary

More than two thirds of the UK’s oilseed rape crop is treated with a herbicide containing metazachlor. Following best stewardship practice and correct application timing could be key to retaining its future use.

Operators applying metazachlor and quinmerac, the weed control actives, which are contained in numerous oilseed rape herbicides, must follow best practice guidelines to protect water.

If stewardship action is not taken, the use of product containing the active ingredient could be severely restricted, or their use revoked.

The measures, under the Metazachlor Matters heading, were developed as part a European-wide initiative by approval holders Adama and BASF and contain guidelines that set deadlines for autumn weed control treatments that contain metazachlor. To view these guidelines, follow the link HERE

best practice for applying Metazachlor

Don’t delay spray

Products should be applied early, on to well-structured seed beds so that they do their job of protecting newly emerged seedlings from invasive weeds, while also ensuring the active is subsequently broken down and the risk of movement to water later in the season is avoided.

Drained fields, located in drinking water ‘Safeguard Zones’, should be applied by 1st October. To find out if you’re in a Safeguard Zone go to the Environment Agency website – What’s in your backyard? You can find the link HERE

Drained fields, not located in Safeguard Zones, have the extension opportunity to 15th October, where soil and seedbed conditions are good, and drains are not flowing. There are no restrictions for undrained land.

Good establishment

Getting establishment conditions right is crucial. A fine tilth on top, to a consistent half inch depth allow rapid establishment and prevents both slug issues and vulnerability to adult flea beetles.

These conditions also increase crop competitiveness to work in tandem with the herbicide in controlling damaging weeds such as poppy, chickweed, shepherd’s purse and cranesbill.

How to protect water

Metazachlor and quinmerac get into water through two sources:

  • In the farm yard – handling/sprayer cleaning. This can be avoided by good operator practice and adopting Voluntary Initiative guidance. You can find the link to the Voluntary Initiative advice HERE and you can also find our training course on mixing and filling on the NRoSO pages (NRoSO members only) HERE
  • In the field – via surface run-off, field drainage. Rainfall events have a big impact – you cannot control the weather, but you can reduce the risk.

Early establishment is key to prevent metazachlor and quinmerac moving to water. In addition, reducing the application rate will cut concentrations in drainage water

Application before drain flow starts and good soil structure/seed bed preparation will minimise potential for movement to surface water.


Best Practice to protect water:

  • Fill sprayer in a bunded area and clear up any spills immediately
  • Ensure there is a 6m grass buffer strip next to water courses
  • Wash sprayer down in the field or in a bunded area
  • Do not apply when soils are cracked, dry or saturated, or if drains are flowing
  • Do not apply if heavy rainfall is expected within 48 hours of application, because this can lead to significantly higher losses to water.
Sprayer operator filling an induction hopper

Maximum dose rates

  • Metazachlor: 750gm/ha
  • Quinmerac: 250gm/ha

Lower dose rates reduce the risk of movement to water and can give equivalent control especially when applied in combination with other herbicides. Check required dose with your BASIS-registered adviser.

Oilseed rape filed and field boundary
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