24 May 1996

Mixed tactics beat blackgrass

By Andrew Blake

USE multi-pronged control tactics if you hope to contain resistant blackgrass.

That familiar message is reinforced by new East Anglian trials.

The experiments, set up by Banks Agriculture at Sutton St James, Lincs reflect a growing need to provide local answers for local problems, says technical services manager Judith Brightman.

Three new areas – Lincs, Beds and Herts – have been added to the firms main demonstration site at Eynesbury near St Neots, Cambs. Blackgrass resistance to fenoxaprop (as in Cheetah, Puma and Wildcat) has been confirmed in samples from the Sutton St James field, notes Ms Brightman.

"Blackgrass resistance is certainly something we need to address," she says. Although generally few farmers, especially those in the fens with plenty of cereal breaks, perceive it as a problem, having sound strategies to deal with it where it occurs is vital.

That philosophy extends to application rates – the Lincs trial, comparing a range of different herbicide treatments (see table), used only full label doses. "There is no point in messing about if you have got resistance."

Blackgrass in the Sutton St James field, in Brigadier wheat after wheat, was severe and fairly uniform at the outset. But some patchiness is inevitably reflected in the results, says Ms Brightman.

A strong finding concerns cultivation. "The answer to blackgrass doesnt just come out of a bottle. Control after ploughing is vastly better than after minimal cultivation." That applies even though ploughing in last years dry autumn led to poorer establishment, and despite slugs later thinning the ploughed stand and reducing the crops competitiveness, she stresses.

Minimal cultivation imposes such a challenge that even two very promising experimental herbicides, expected to be on the market soon, gave little more than 50% control without the aid of Avadex (tri-allate) granules.

The value of applying a range of different active ingredients at various timings is reflected in the use or otherwise of the granules immediately after drilling. In nearly all cases they usefully boosted control, she notes. "By ringing the changes you reduce the resistance pressure."

One exception to the multi-active approach seems to be the use of IPU (isoproturon) which worked surprisingly well alone, especially after ploughing and Avadex. The finding could help those campaigning to retain the chemicals current application rate in the face of possible cuts to protect water sources, suggests Ms Brightman.

Comparing results from Puma/Treflan combinations emphasises the need to use the latter pre-emergence rather than as a mix, she adds. "Provided you can get on it gives you another timing for another hit."

Growers may see the results at an open day on June 19. For details call (01767-680351).


Blackgrass survivors (plants a sq m) assessed on May 3 in Banks Agriculture herbicide trials at Sutton St James, Lincs

Spray application datesPre-treatment measures

Dec 4, 1995Feb 29, 1996Min cultMin cultPloughPlough

+ Avadex+ Avadex

UntreatedUntreated170625835

IPU-8739121

IPU + Treflan-1052993

IPU + TreflanWildcat96321110

IPU + TreflanTopik + Actipron1084893

IPU + TreflanTopik + Actipron97281511

(Apr 10)

Puma X-127422720

Puma X + Treflan-13831157

Hawk + Actipron-112483710

Wildcat-126233021

Grasp* + Output-9336296

Grasp* + Output

+ IPU-11327278

Grasp* + Output

+ Trump-142322111

Trump-98442829

Trump + Dagger-97252011

Experimental A-115283011

Experimental B-9335171

Exp B + Treflan-7744217

Pre-em Treflan +

exp B-75633824

Pre-em Treflan +

Puma X-6621318

Actives: Avadex (tri-allate); IPU (isoproturon); Treflan (trifluralin); Wildcat (fenoxaprop-P-ethyl); Topik (clodinafop-propargyl); Puma X (fenoxaprop-P-ethyl + isoproturon); Hawk (clodinafop-propargyl + trifluralin); Grasp (tralkoxydim); Trump (isoproturon + pendimethalin); Dagger (imazamethabenz-methyl). Actipron and Output are adjuvants.*No label recommendation for autumn use.

Resistance has been confirmed at Banks Agricultures Lincs trial site. But ploughing has done much to ease the weed pressure, says Judith Brightman.