The way that winter and spring cereals are defined for pesticide approvals has changed and will affect how some products can be applied.

From 1 January 2015, the Chemicals Regulation Directorate (CRD) moved from using variety as the deciding factor for defining a winter or spring crop to drilling date.

The definition of winter or spring crop for CAP “greening” purposes remains defined by variety type as stated by the breeder.

The CRD told Crops that for the risk assessment underlying pesticide authorisations, time of year of application is much more important than the variety to which it is applied.

This is largely due to different weather patterns and how wildlife uses the crop.

It will have the biggest effect on products approved for use in winter cereals only and examples include Dow AgroScience’s two cereal herbicide products, Unite and Broadway Star.

Both are approved for use in winter wheat and Dow will continue to support applications in winter varieties sown before 1 February, but will not support use in spring varieties sown before 1 February due to concerns over crop safety.

Winter varieties sown on or after 1 February are now classed as spring crops and as such, any applications of these products will be illegal under the CRD’s new rules.

Check label

The company’s customer agronomist, Stuart Jackson, said pyroxsulam – the common active ingredient in the two products – at full label rate can damage spring wheat variety due to its reduced ability to metabolise the active.

“If you are sowing a spring cereal variety prior to 1 February, before you apply a product approved for winter use, check if it has a spring approval too.

“If it has, then it should be fine, but if it hasn’t, why not? It may be legal to apply, but there could be a crop safety issue,” explained Mr Jackson.

The complication will only exist in the short term and as products are reregistered, labels will change to accommodate the new rules and provide more precise guidance.

Until then, Mr Jackson advised growers who are unsure to consult the product manufacturer or speak with their Basis-qualified adviser before applying.