No sulfonylurea sequence agreed

Sequences of the grassweed sulfonylurea herbicides Lexus and Atlantis appear likely to be made illegal by the Pesticide Safety Directorate, according to herbicide resistance expert Stephen Moss.

The Rothamsted researcher told the HGCA R&D conference PSD has proposed no more than one sulfonylurea grassweed herbicide should be used per crop.

“So you won’t be able to use Lexus followed by Atlantis.”

The proposal will also restrict the use of any ACCase inhibitor active ingredient, such as clodinafop, to one application per crop, but growers would be able to use two different products during the season.

“As I understand it you couldn’t use Hawk in the autumn followed by Topik in the spring [because both contain clodinafop], but you could use Hawk followed by Cheetah.”

Restrictions are tougher for sulfonylureas than fops or dims because resistance in much less common in the group, PSD says.

“The proposal is aimed to avoid the situation ACCase inhibitors have reached, and will help clarify the use of any ALS inhibitor in sequence with another is not approved for resistance reasons.”

The move comes after a special Weed Resistance Action Group meeting in September 2005 was called to discuss the implication of sequences of high-risk grassweed herbicides.

“Following the meeting PSD took these proposals to the ACP, which they have now agreed,” PSD’s senior herbicide agronomist Ingrid Hoy says.

The next step is drawing up an implementation plan, which industry will consult on, about the impact on individual products, with the aim of having the restrictions in place by next autumn.

In the meantime growers should continue to follow the advice given on product labels, she says.

The restrictions are likely to have been a “bombshell” for Lexus manufacturer DuPont, Dr Moss admitted.

The firm had been hoping to get approval for a Lexus/Atlantis sequence.

Sequence restrictions do have a number of implications for DuPont’s application, the firm’s technical manager Steve Cranwell admits.

“We’re going to have a discussion with PSD about our application.

But the industry also needs to have a dialogue about how whatever is proposed is implanted.

It was clear from the meeting growers and advisers wanted to have flexibility, and this potentially could make life more difficult for growers.”

Dr Moss supported the restrictions.