Chemistry

1. Why are we still striving for that “silver bullet” if it’s never going to work?

Cultural control is key to sustainable black-grass management, but such measures can only go so far and herbicides will always be needed for sustainable and profitable crop production, says Mr Anderson-Taylor.

“Control of some existing chemistry may be limited, but that’s not an excuse to not keep striving to find other solutions. We believe we will find something.”

Mr Lloyd also believes chemical options will remain an important part of future black-grass control strategies, although he warns growers that even if new products are found, it is not possible to “spray our way out of trouble”.

“Chemistry can help make a difference if we use products sensibly and reduce black-grass populations to a controllable level with other cultural measures first.”

2. What is the most effective chemistry programme going forward with the limited chemistry available?

Pre-emergence chemistry based around products containing flufenacet should form the backbone of chemical black-grass control, say experts.

Mr Lloyd urges growers not to compromise pre-em application timing and even in very dry seasons it is worth applying at true pre-emergence timing and not delaying sprays, as active ingredients retain efficacy for some time and will be on the seedbed, ready to work, as soon as sufficient moisture is available.

“Once black-grass hits one leaf, efficacy drops 50%, so pre-ems have got to be applied early.”

Stacking chemistry can be worthwhile, particularly for earlier-sown crops under higher black-grass pressure, adds Mr Cotton, who sees value in products based on actives such as flufenacet, diflufenican, pendimethalin, tri-allate and prosulfocarb.

“As drilling gets later into October, the impact of chemistry stacks can diminish as black-grass growth is slower, so you don’t need exotic stacks for late drilling. The efficacy of flufenacet also increases into November, so there may be an opportunity to save some cost.”

Atlantis can still play a valuable role in chemistry programmes, even in the presence of resistance, but it should be used early with a residual partner, such as flufenacet, says Mr Anderson-Taylor. “If resistance is due to EMR, the smaller the black-grass is the better Atlantis will work.”

3. Is late drilling compromising soil-acting herbicides?

Late drilling does not mean residual herbicide efficacy has to be compromised and Mr Hull says active ingredients can perform better when used later as soil conditions can be more favourable.

One trial found a 25% uplift in control from Liberator and Defy applied later compared with an earlier application timing, he says.

“Late drilling for me is the first couple of weeks in October,” he notes.

Mr Lloyd advises anyone drilling late in the season to ensure primary cultivations are done early in good conditions after harvest to ensure a good seedbed for successful crop germination and efficacy of residual chemistry.

4. What is the best and most cost-effective chemical strategy in oilseed rape?

Black-grass control in oilseed rape can be challenging, but it is still possible to achieve good results from the crop. Maximising crop competition with good establishment is essential, but deciding on the best approach to establishment and weed control must be done on a case-by-case basis, says Mr Cotton.

Mr Hull says resistance to the ACCase inhibitor clethodim is an increasing threat and urges growers not to over-rely on products containing this active. “Resistance is in a low proportion of the weed population at the moment, but it is a high-risk herbicide, so the more we use the active the greater the risk of resistance developing.”

Any application should be followed with another active grassweed herbicide to maximise control, he says.

5. Where are we with new chemistry and why has it not been possible to find an active ingredient that will provide good black-grass control for the next 10 years?

A major new herbicide is typically launched every 10-15 years and while manufacturers acknowledge it is becoming harder to find and develop new active ingredients, Mr Anderson-Taylor is confident new products will be found in future.

Bayer screens around 100,000 potential active substances and spends some £300 million to bring each new product to market and the firm remains committed to finding new products, he says.

However, he acknowledges the challenges in the industry are “immense”, particularly when it comes to getting new products through increasingly stringent environmental and safety regulations.

6. If they were to be farmers, do you think my unborn grandchildren will be battling black-grass?

Yes. The ability of black-grass to evolve and adapt to different selection pressures means it is inevitable the weed will be around for many more years to come.

Growers have to employ a variety of chemical and cultural measures to tackle the problem, which is made even more challenging in the presence of herbicide resistance.

Make the most of the latest advice to combat black-grass on your farm and stay up to date with the latest black-grass news by following @DrBlackgrass on Twitter, or use #BGLive to have your say on the debate. For your chance to attend similar events in the future, sign-up to the Black-Grass Task Manager: cropscience.bayer.co.uk/bgtm