Black-grass remains a focus of concern for growers and advisers alike, which is why a recent BASIS podcast took an in-depth look at the topic, ranging from cultural techniques to chemical options.

For the past nine years, Rothamsted Research has been running a farmer network to monitor black-grass populations and the effects of different approaches to its control.

Today, the network covers more than 180 fields on some 60 farms across the country.

Technician Richard Hull reflects that some farmers have made big changes to their systems and got on top of the weed.

However, there are many who, despite undertaking change, have slipped up in one or two areas of detail and made little progress.

While some who have not made changes have just seen infestations become worse.

Different farmers have different views of what satisfactory control is.

For some, success is only achieved when hand-rogue able levels of infestation are achieved, while others only pay attention when there is a clear impact on yield or margin.

Mr Hull points out that just 10 plants/sq.m, equates to 50 seed heads, which will be capable of returning 5,000 seeds to that sq.m.

In his view, effective control requires a strategy for a period of five to 10 years, encompass ing issues such as cultivation type, sowing date, cropping, spray regime and so on.

As important is to review the success of the strategy each year and be prepared to change.

Farm network results show that delaying drilling from mid-September to mid-October can see a 30% reduction in black-grass population, but far larger reductions of up to 90% fewer plants can be achieved by a switch to spring sowing.

Wet weather However, on some soil types this comes with increased risk of wet weather or dry springs.

The ability of black-grass to adapt and resist chemical treatments is discussed by Stuart Kevis, business development manager at BASF.

He recommends testing regularly for the presence of herbicide resistance to establish if it is present in crops and whether it is target or non-target site specific in nature.

No spray treatment will provide anything like a com plete answer to managing black-grass, but attention to detail in choosing and applying chemicals will significantly improve the level of control which can be achieved.

Mr Kevis says a pre- and post-emergence programme will be effective, but where possible the pre-em should be applied within 48 hours of drilling.

Control will also be improved by ensuring a firm, moist seedbed with little trash that could reduce evenness of spray coverage.

Crop and variety type also affect the competition that black-grass will face, says Paul Roche, Syngenta product placement lead.

Hybrid barleys that are so vigorous above and below ground can compete strongly with black-grass and reduce seed return by more than 300%, compared to conventional cereals, he claims.

And this population reduction occurs whether or not herbicide tolerance is present.

Even with conventional varieties, he stresses the importance of good establishment, which depends on good seedbeds and well-timed sowing dates.

Crop nutrition has a part to play as trials have shown the importance of early N applica tions in February, around growth stage 25, to boost crop growth and increase weed suppression.

Detail Mr Roche also highlights the importance of attention to detail in machinery hygiene and selecting effective seed rates.

Where populations are particularly severe, consideration should be given to burning off the crop with glyphosate or, with correct timing, taking whole crops for anaerobic digestion.