Farmers cannot now use or store any products containing the herbicide isoproturon (IPU) after it was banned from being used from Tuesday.

UK approval for all products containing IPU was revoked by ministers on March 19, 2007, after a review of its impacts on the aquatic environment. Farmers had until June 30 this year to use up or dispose of remaining stocks. Continued use or storage on farm after this date is illegal.

NFU deputy president Meurig Raymond said: “At a time when we are calling for voluntary measures rather than red tape and regulation, it’s vital that all farmers act responsibly. Any leftover stocks of IPU must be disposed of through a licensed waste disposal contractor.”

Dr Bob Breach, Voluntary Initiative Water Sub-Group chairman, said: “Water companies and regulators will monitor IPU for the foreseeable future and they will be very disappointed to see any significant levels of IPU this autumn. It’s easy to detect very small amounts of IPU so any one letting the side down will easily be spotted.”

The Voluntary Initiative is a programme of measures, agreed with government, to minimise the environmental impacts of pesticides. To date, nearly £60 million has been invested in the scheme by the agricultural industry.