BCPC Weed Review looks at the weed challenges over the past 50 years

Over 90 delegates attended the 50th BCPC Annual Weed Review chaired by Dilwyn Harris, Dow AgroSciences and held at Rothamsted Research, Harpenden on 14 November. “Significant arable weed control challenges have faced farmers, scientists and the industry over the past half-century,” explained Mr Harris. “This review has given us the opportunity to reflect on the hurdles encountered and consider the progress made. It also provided a platform for post-graduates to profile their current weed research in the poster session.” 

Kicking off proceedings, Bob Froud-Williams, ex Reading University titled his session Fifty Shades of Weed Research. “Over the past 50 years, selective herbicides have significantly modified the weed flora. Alternative herbicides have been introduced and there has been the inevitable development of resistance,” he said. “Weed populations have been subject to oscillation and herbicides have influenced species prevalence and the decline in density in seed banks. There have also been changing attitudes to weeds with agri-environment schemes and the importance of biodiversity encouraging more game cover and wild-bird seed mixes to be planted. Horticulture, once the recipient of herbicide development, is now in crisis as many herbicides are relegated to the litterbin. What we have achieved though is a multidisciplinary approach to weed science, an increase in weed knowledge, biology, persistency in the soil, demographics and how to manage weeds and resistance. The decline in expertise in weed science in recent times needs to be addressed to ensure effective future weed management.”

In an extremely visual presentation, Noel Nelson from The Met Office looked at Weather patterns in the UK. “Although variations do exist from year-to-year the general weather pattern in the UK is of a temperate climate,” explained Noel. “Average weather considers a 30-year period and is a good marker of what is happening but it does mask variability especially of rainfall which can be very localised and more complex to understand. What we are seeing is a trend to more heavy rainfall events increasing in the winter and falling in more intense bursts.” He explained that although the Met Office and other global models show an increase in rainfall and they are confident that warming is occurring, they are less confident in the amount of warming. “The ingredients are there for climate change with warm, wet and dry extremes but the natural variability is large and will dominate the climate in the near future,” he said.

Following on Jim Orson, NIAB/TAG considered weather patterns and how they can effect weed infestations and herbicide control. The UK is one of the top three countries along with Ireland and New Zealand that can sustain high wheat yields and this seems to be due to its island location along with the soil and climate. “In the UK we are very reliant on the weather and there has been a trend to autumn spraying which provides more reliable control,” explained Jim. “Black-grass control in autumn sown cropping systems is increasingly dependent on rainfall as the activity of some products is more affected by drought than others. It is vital for farmers to use weather forecasts and think around the issues so that optimum performance is achieved.”

Andrew Cotton, Cotton Farm Consultancy discussed weed control in spring cereals explaining that in his experience the dominance of winter cropping has lead to the development of resistant black-grass especially on heavy soils. “Effective use of stale seedbeds and spring cropping in the rotation could well be an answer to some of the black-grass issues,” he said. “Spring crops need more promoting. There also needs to be more R and D and more pre-emergence herbicides. Spring crops can be very profitable too even at 2.5 tonnes per hectare, input costs are lower and it is better than leaving the land fallow.”

Plant Growth Regulators (PGRs), which affect plant growth by altering the growth hormone levels, have played an important role in crop production over the past 50 years. “PGRs don’t lose efficacy so chlormequat, which was first introduced in the 60s, is still the most effective on cereals in terms of reducing crop height and reducing lodging. In fact 87% of wheat grown in 2012 had a PGR,” explained Pete Berry, ADAS. “The benefits of using PGRs are significant, the cost of lodging if PGRs are used in wheat is estimated at £108m. This rises to £196m if no PGRs are used. In oilseed rape things are slightly different as all PGRs are registered fungicides however the cost benefits are similar with the cost of lodging estimated at £64m when PGRs are used compared to £86m when they are not used.”

One of the key problems in controlling weeds over the past 50 years has been industrial consolidation, external pressures, regulations and new approaches to discovery. Anne Thompson, Dow AgroSciences took the audience on a trip down memory lane showing how companies had changed. “Back in the 60s there were around 42 US and European research based agchem companies, today there are just six or seven” revealed Anne. “Companies have been removed and generics have increased as products come off patent. In 1962 Rachel Carson wrote “The Silent Spring”, this changed public perception and gave increased attention to the regulation and use of pesticides – but also the fear of pesticides. What people do not consider though is the dose. All things can be poisonous but it is the use of the appropriate dose which permits safe treatment.”

“There has been an exponential growth in regulations. The Water Quality Directive has been updated many times but the 0.1 micrograms per litre as a trigger value for water contamination remains unchanged from the 1980s – this is a big hurdle for herbicides. New regulations are on the horizon and these increase the cost and time for developing a new pesticide. The average cost today is over $256million and the time for development from initial discovery is now 10-15 years. We have the techniques, powerful databases, high throughput screens, virtual screening technologies and genomics – all this is happening but it all depends on the success of the scientist to have the initiative and curiosity to discover. We need to follow the innovation principle – to balance precaution and proportion in regulation and not let precaution stifle innovation. We can meet the challenge of the future if we are allowed,” concluded Anne.

Focussing on black-grass, Stephen Moss, Rothamsted Research highlighted that in general £100 per hectare is spent on herbicides but we may only get about 20% control of black-grass. “How do we get out of this mess?” he asked. “It is now accepted that some degree of resistance occurs on virtually all farms on which black-grass herbicides have been used regularly for the last 25 years. Farmers will carry on spraying with e.g. Atlantis, where there is no alternative, even if they are only getting poor control. And, with an ever-increasing trend to drilling in the autumn we are handing it to black-grass on a plate.”

“Farmers need to seriously consider non-chemical control methods,” advises Stephen. “Rotational ploughing once every three to six years with good inversion can control black-grass by some 69%. Delaying drilling will result in lower black-grass populations and give better control from herbicides. Fallowing for two or three years can also give significant reduction of the seedbank. The other key advantage of non-chemical methods is there is no resistance and this may pay long-term dividends. It is important to let the farmer make the decision – preaching can be counter-productive. However, involving farmers in their own simple trials can help them to find out what works on their farm – knowledge without application is wasted.”

The final interactive session from Jon Storkey, Rothamsted Research considered future challenges for weed science. “We are facing a rising world population, the need to produce more food from less land, global warming and a decline in available herbicides. We do not have all the weed control answers for the future,” explained Jon. He then continued by asking the audience to vote in response to a series of questions about the future. The audience thought that herbicides were unlikely to be the mainstay of future weed control and a as consequence winter cereal areas would decline. The audience was also prepared to allocate 1-5% or 5-10% of their land to enhance the diversity of farming landscapes. They also thought that there would be a rise in new (invasive) weed species in the next 20 years. Finally the majority felt that current funding of research in weed science was inadequate – all food for thought for the future.