Be flexible with herbicides to beat blackgrass

5 November 1999

Be flexible with herbicides to beat blackgrass

FLEXIBLE herbicide programmes based on Hawk (clodinafop + trifluralin) can tackle all blackgrass problems – from low, sensitive populations right through to increasingly common difficult and resistant infestations, two crop consultants agree.

Although some authorities say fop herbicides should be reserved for break crops, Farmacys Jim Butchart disagrees. "Alternative chemistry should be used in break crops. Cereal growers should use the strongest chemistry they can, but always in mixtures and/or sequences.

"In trials and commercial use clodinafop gives reliable, high levels of control when applied as a co-formulation with trifluralin after pre-emergence sensitising with either Avadex (tri-allate) or Prebane (terbutryn)."

Novartis has issued a new guide to Hawk doses, mixtures and sequences, according to blackgrass growth stage and sensitivity, and other weeds present.

While a rate of 1.66-2 litres/ha is suitable for low to moderate blackgrass infestations, once the weed starts to tiller rates need to go up, says the firms Andy Pigott. "For high populations of difficult blackgrass, Hawk needs to go on at the full 2.5 litres/ha." For resistant populations, the full rate should always be used.

Where chickweed, annual meadow grass and mayweeds are present, it can be tank-mixed with 500-1000g/ha of IPU. But for other broadleaved weeds like speedwells and field pansy, diflufenican should also be added, he advises.

Mr Butchart agrees with the recommendations, but questions how many sensitive populations of blackgrass remain in his area. "IPU used to give control in the high 90%s," he says. "Now it averages 65-85%."

He sees only limited opportunities to use Hawk below 2.5 litres/ha. "On difficult or resistant blackgrass I would advocate Avadex or Prebane pre-emergence, followed by the full rate at GS12-13 of the blackgrass. Timing is critical. Delay is likely to result in disappointment.

"Target site resistance has increased rapidly in recent years. Over 50% of tests we conducted last year had both resistance mechanisms present. In these cases or where poor control has occurred but resistance testing has not been done, Hawk should be mixed with Lexus (flupyrsulfuron) at the full rate of both."

David Ellerton, Procam technical director, agrees with the Novartis guidelines, but stresses that blackgrass should not be considered in isolation. "You have to consider it with broadleaved weeds. Where they are present, and to boost residual wild oat control, growers should add pendimethalin. And to widen the broadleaved weed spectrum I would add Harlequin (IPU + simazine), rather than mix in straight IPU."

To increase broadleaved weed control still further, Dr Ellerton recommends adding products containing diflufenican, such as Bolero (with terbuthylazine). And rather than mix Lexus with the Hawk, he would add Lexus Millennium (flupyrsulfuron + thifensulfuron). "It does the same job as straight Lexus on blackgrass, but brings in more broadleaved weeds." &#42


&#8226 New Hawk guidelines.

&#8226 Appropriate doses.

&#8226 Mixtures and sequences.

&#8226 Sensitising treatments.

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