New tank mix guidelines to help winter wheat growers unable to apply a pre-emergence black-grass herbicide are being put forward by Syngenta.

The new 'holding spray' tank mix of Defy + Topik could offer a useful fall-back for treating black-grass once it reaches 1-2 leaves if growers have been unable to apply a pre-emergence herbicide, says Syngenta technical manager Iain Hamilton, to help stop it getting out of hand later

Designed for use once black-grass reaches the 1-2 leaf stage, the new guidelines for mixing residual herbicide Defy with contact-acting Topik offers an important fall-back if growers miss the earlier timing slot because of workload pressures or weather delays, says Syngenta technical manager, Iain Hamilton.

It essentially offers an alternative to isoproturon-based “holding sprays” which have previously been popular in these circumstances, he points out.

“With field operations compressed into a shorter window after the wet harvest, there’s a real risk of black-grass growing beyond the optimum timing for a pre-emergence treatment in some fields this season,” says Mr Hamilton, “especially if growers are concentrating on drilling other fields, rather than spraying.

“Using a holding spray offers an option for targeting black-grass which has already emerged with the Topik element, while also laying down a residual foundation against later-emerging weeds with the Defy component.

“Averaged out across trials, a mixture equivalent to 3 l/ha of Defy with 125 ml/ha of Topik and adjuvant applied at the 1-2 leaf stage has given around 98% black-grass control when used as part of a programme – similar to that from a tank mix of isoproturon with Hawk (clodinafop + trifluralin).

“Clearly, applying a pre-emergence herbicide is the first choice in black-grass situations. But whether you apply a pre-emergence treatment or holding spray, the important thing is to make an application – so that you’re not leaving the later sulfonylurea treatment to do all of the work.”

This season, especially, Mr Hamilton says robust in-crop control could be particularly important with black-grass because more of it is predicted to emerge over a longer period, due to its high seed dormancy.

“Using a holding spray or pre-emergence treatment also fortifies programmes if concerned about resistance or variable control from a post-emergence treatment, such as a sulfonylurea” he adds.

“The benefit of the new Defy holding spray option is that if you’d been planning to use Defy as your pre-emergence treatment anyway, you can still use it in this mixture rather than buying a different herbicide, just that the timing is slightly later.

“Indeed, if the holding spray option works well enough, you may be able to save the cost of a post-emergence treatment.”

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