Four factors spark blackgrass growth frenzy

Blackgrass is creating huge problems in early drilled winter wheat crops with the aim now to tackle any weed flushes before they reach the three-leaf stage.

Independent agronomist Richard Cromie says using a prosulfocarb-based herbicide could play a big role in achieving maximum control.

On the earliest drilled crops, Mr Cromie who is based in the south of England, is set to make the first post-emergence applications of mesosulfuron + iodosulfuron in late October or early November, and will add prosulfocarb (Defy) where blackgrass is a big problem.

“The best partner I’ve found when there is bigger blackgrass has been a prosulfocarb product,” he adds.

Iain Hamilton, field technical manager at Syngenta which makes Defy, says four factors including early drilling, low dormancy of blackgrass seed, good seed-beds and dry weather will have increased the blackgrass pressure this autumn.

Wheat drilled before 25 September is likely to have seen the biggest flushes of the troublesome weed with the low dormancy compounding the problem in these crops.

Good seed-beds have encouraged both crop and weed growth and the dry period experienced at the start of the autumn may have hindered the activity of some of the soil-applied herbicides according to Mr Hamilton.

If growers are to maximise yield and reduce blackgrass seed return this season, he stresses it will be important to remove the surviving blackgrass flushes before they reach the three-leaf stage.

Mr Hamilton says if the herbicide Defy hasn’t been used, it should be considered as a residual partner in a grower’s post-emergence mesosulfuron + iodosulfuron blackgrass treatment.

“Trials have been conducted on this tank mix, and adding Defy to mesosulfuron + iodosulfuron has given an extra 10% blackgrass control. Consider using Defy at 2-3 litre/ha with mesosulfuron + iodosulfuron,” he suggests.

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