Resistant blackgrass is tough challenge for all

7 February 1997




Resistant blackgrass is tough challenge for all

Tackling herbicide resistant blackgrass is much more challenging than first thought. That was the worrying message from a meeting of specialists last week

COPING with herbicide resistant blackgrass is proving far more tricky than researchers first thought.

Delegates at last weeks Association of Applied Biologists conference at Rothamsted recognised the urgent need to stem the spread of herbicide resistant blackgrass. But how best to do that was hotly debated.

Despite plenty of research, herbicide resistant grass-weeds remain a serious and growing problem in the UK, stressed the HGCAs Dr Chris Rawlinson. Since the late 1980s £0.25m of levy cash, often with MAFF backing, has been spent trying to find solutions and offer guidance to growers. "We have agreements in principle, but there are differences of opinion and some huge unknowns."

Resistance mechanisms are probably more complex than first thought, explained Dr Stephen Moss. But, whatever means is involved the sooner resistance is spotted the better, he said.

Watch out for individual plants surviving specific herbicides in particular, he advised. Growers finding them should stop using such materials on affected fields. "Ease off the fops and dims or you can very rapidly get into serious trouble."

Relatively few growers seem willing to pay the £60-100 cost for testing for resistance in the field.

Dr Rawlinson saw a pressing need for a simple diagnostic test. But one currently under development at Rothamsted is unlikely to be available commercially by next autumn.

ADASs James Clarke questioned whether anti-resistance messages were being put over as effectively as they might. There were signs that manufacturers were more prepared to give information than distributors, he said.

Choice of herbicide mixtures and sequences was especially contentious, said Mr Clarke. He urged suppliers not to muddy the waters by confusing mixes aimed at improving the spectrum of weeds controlled with others intended to help counter resistance.

Drawing parallels with insecticide resistance, Rothamsted entomologist Ian Denholm cautioned against using mixtures. "They can promote crises by masking resistance until both ingredients become ineffective. Its a real concern."

The timing and thrust of advice on cultural control could be improved, Mr Clarke suggested. He highlighted trials showing the value of delayed autumn drilling, which in practice few growers, especially those on heavy land, wish to practice. "Perhaps we should say avoid very early drilling."n

Strategies for coping with herbicide resistant blackgrass are coming under increasing scrutiny. According to IACR Rothamsteds Steve Moss, complex resistance patterns are probably to blame, making it difficult to identify the best approach for each field. Avoid the problem in the first place, he warns.


BLACKGRASS RESISTANCE


&#8226 Growing threat to cropping.

&#8226 More complex than thought.

&#8226 Counter measures debatable.

&#8226 Containment messages confusing.

&#8226 Need for more open consensus.


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