Growers applying a sequence of two sulfonylurea herbicides with grassweed activity this season could be risking prosecution, as well as increasing the chances of grassweed resistance on their farms.
Despite a new statement prohibiting such sequences being placed within the statutory box on the labels of grassweed-active sulfonylureas, such as Atlantis (mesosulfuron-methyl + iodosulfuron-methyl-sodium) and Lexus SX (flupyrsulfuron-methyl), considerable confusion remains among agronomists and growers, Ingrid Hoy from the Pesticides Safety Directorate notes.
“I’m not quite sure why. The sequence [of flupyrsulfuron-containing products and Atlantis] has never been approved. The new regulations maintain the status quo.”
GRASSWEED SU SEQUENCES
But there is still confusion over what sequences are actually illegal to apply, says UAP technical manager Chris Bean, particularly where growers are using up old stock in the supply chain that doesn’t have updated labels.
“One interpretation is it is only the [information in the] statutory box that is a legal requirement.” Approved sequences are not written into the statutory box information.
That interpretation would allow growers to apply a sequence even if it didn’t appear on the approved list of sequences on the product label, as long as it didn’t contravene the statutory box restrictions.
But Mrs Hoy says only the approved sequences can be legally applied. “I have in the past clarified this with our enforcement officers, and those statements [not in the statutory box] are not simply advisory – they are restrictions on use. In theory, a grower could be taken to court, as it would constitute an unapproved use of a product.”
Lexus manufacturer, DuPont, in direct contrast to both Bayer and PSD, says existing stock does not fall under the new restrictions.
While the firm supports the new guidance, says technical manager Steve Cranwell, any existing stock in the supply chain should be used as per its label and conditions of use.
“By July 2007 all labels will have to carry the new restrictions and the current confusion will, hopefully, be eliminated.”
But as, if not more, importantly such a sequence could increase the resistance risk on your fields, Mrs Hoy says. “The restrictions were put in place because of resistance, that’s what should be uppermost in peoples’ minds.
PSD would not have done it if our experts didn’t consider it a serious risk.”
But not all agronomists are convinced the resistance risk is high, including ProCam technical director David Ellerton. “I’m much more concerned about the misuse of Atlantis. That pushes resistance much harder than using a well-timed sequence.”
But it would constitute an unapproved use of the product, Mrs Hoy reiterates. “The bottom line is even if the restrictions are not yet on product labels in stores, growers should still be using products in line with these restrictions.
As far as PSD is concerned there should be no ambiguity on this.”
NEW APPROVAL CREATES GREY AREA
Agronomists are also confused by PSD’s decision to approve a flupyrsulfuron product, DP459, without any grassweed control claims on the label.
The new statutory box wording on the Atlantis label specifically prevents the use of other grassweed-active sulfonylureas in sequence with the product.
Approving DP459 without reference to its grassweed activity on the label has further muddied the waters, Mr Bean says. “It is a crazy situation. On the one hand we have the new wording in the statutory box, and on the other, PSD has approved a product that creates a loophole.”
Mrs Hoy agrees DP459 has created extra confusion. But she says the same restrictions still apply, and it would be illegal for growers to use it in sequence with Atlantis. “For it not to apply, a product should not apply a selection pressure on grassweeds. This product does and so it has the [statutory box] restrictions on the label.”
The PSD has published a list of products affected by the new restrictions on its website to help growers and advisers, Mrs Hoy concludes.