The grey area of whether it was legal to use a sequence of two grassweed-active sulfonylurea herbicides has been clarified by new restrictions put in place by the Pesticides Safety Directorate on the use of at-risk active ingredients.

After consultations with the Advisory Committee on Pesticides and Weed Resistance Action Group, PSD has decided to make it a statutory condition of use that no more than one ALS inhibitor-containing product with claims for control of grassweeds can be applied to a crop in a season.

So the sequence of Lexus followed by Atlantis is still not approved.

Growers will also be restricted to just one application of each ACCase inhibitor (ie fop or dim) active ingredient to a crop in a season, although a second fop or dim active ingredient can be applied to the same crop, providing it is being used to control different weeds at different timing.

In other words a sequence of Hawk in the autumn for blackgrass control followed by Topik in the spring for wild oats would not be allowed because both contain clodinafop-propargyl, but Hawk followed by, for example, Axial or Cheetah would be OK.

The new restrictions are intended to ensure all growers use high resistance risk grassweed herbicides responsibly, PSD says.

It also brings older products into line with those subject to more modern risk assessment procedures.

Manufacturers of affected products should have been issued with revised Notices of Approval detailing the changes required last month.

Labels of new stocks of products must be amended within 12 months, but the restrictions will still apply to products already in stock without label amendments.

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