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Black-grass: the farmer’s nemesis

Visit an arable farm in England, particularly in its central and Southern parts, and ask the farmer what their number one problem is on their farm. They will most likely tell you it is black-grass.

For Plant Facts Week 🌱 Laura Crook takes a look at black-grass.

black-grass and wheat
Spot the black-grass. Photo: Laura Crook.

The innocent and almost attractive looking black-grass (Alopecurus myosuroides) is a competitive agricultural weed species that affects arable fields, mainly in crops of winter wheat. Its success is threefold; autumn germinating to coincide with winter crop establishment; high competitive ability with other cereals; and its ability to resist the herbicides applied to try and eradicate it from our fields. Black-grass looks like any other grass, but its the seed heads that give this species its name. The seeds can range from dark green to brown to purple. You can easily spot black-grass during the summer months, as the mature plants stand above the crop and so appear as dark patches across the field.

Traditionally, herbicides were the method of choice to kill black-grass, but over the years most products available to farmers have become less effective. Herbicide resistance in this species is not a new thing – it was first detected in the 1980s. The problem is that currently there are no new chemical modes of action available,and research into producing a new herbicide is a long and costly business. Increasingly, farmers are now relying on cultural methods to control black-grass rather than reaching for the chemical option. This includes drilling winter crops a few weeks later to avoid the autumn flush of germination, planting barley instead of wheat as this provides a better competitive ability against the black-grass, and planting fields in the spring to provide a better chance of the crop establishing with less pressure from black-grass. Changing farming methods is currently the best way of tackling the problem and is vital for maintaining cereal production: it is estimated black-grass costs the farming industry £500 million a year (AHDB).

measuring weeds
Hard at work. Photo: Laura Crook.

I have spent the past three years at Rothamsted Research, an agricultural institute in Hertfordshire, UK, as a research technician studying herbicide resistance in black-grass. Together with the University of Sheffield, Newcastle University and the Zoological Society of London, we are part of a consortium funded on a BBSRC LoLa grant, collectively known as the BGRI (Black-Grass Resistance Initiative). Our aim is to gain a better understanding of this species from gene to field. This has included visiting over 70 farms in England during three growing seasons to map the densities of black-grass found in more than 130 farmer’s fields. We collected seed from these fields to perform large-scale herbicide resistance auditing in order to establish the level of resistance across England. We also collected the management data for these fields from the past 10 years, such as the diversity of herbicides, number of applications, drilling dates and cultivation methods to analyse for comparison between resistance and agricultural practice. Research into the genetics of black-grass constitutes a substantial part of the project. Black-grass is a species affected by target-site resistance, of which a large amount of previous research exists, and nontarget-site resistance, which is less well studied and has been a focus of the BGRI. Target-site resistance occurs when a genetic change alters the shape of the herbicide target enzyme within the plant. Non target-site resistance refers to all other mechanisms of resistance including metabolism of the herbicide molecule and other strategies that prevent the herbicide from reaching its target.

Other research includes studying the genetic structure of different populations of resistant black-grass across the UK. Another outcome of the project has been to produce a diagnostic kit that can be used by farmers in the field to determine whether they have resistant black-grass in their crop. The device is currently undergoing lab and in-field testing before it can become commercially available.

Our role at Rothamsted has largely been to perform the various black-grass experiments in our glasshouses and outdoor facilities such as the large scale resistance audit. For this, we tested over 130 populations of black-grass with four different herbicides, and screened over 65,000 plants to establish the level of resistance across arable farms in England. There are currently 3,000 pots outside, as well as 21,000 plants that have been through the glasshouses in the past 5 months that are being tested for the heritability of non-target site mechanisms through a quantitative genetics experiment. We don’t do small experiments at Rothamsted! My job as a technician is to manage these experiments from sowing to spraying to harvesting, and then recording the data. I love my job because it is always so varied and I’m not afraid to get my hands dirty.

Another major part of our project is to ensure that our research is disseminated to the end user; the farmer who has to face these problems every day. We do this through producing a newsletter, having a website and twitter account and engaging with the various stakeholders involved; farmers and agricultural industry representatives. We have a farmer focus group that we regularly meet with, and last December held a two-day workshop at Rothamsted to discuss all things black-grass. There is also always a presence of our BGRI members at the Cereals agricultural show, chatting to farmers amongst the crop varieties, tractors and much needed bacon sandwiches. Communicating our science is an aspect of our work that I particularly enjoy.

Until I had started working on this project, I didn’t really have an idea of how much a problem black-grass could be for the farming community. But once you’ve walked into a few fields where you can hardly see the crop for the vast swathes of black-grass, you start to get a picture of how devastating it can be for yields. My husband is an agronomist and secretly hopes that I will find the cure. While that is work in progress, I am proud to be part of the research that is gaining a better understanding of black-grass, which will ultimately improve food production in this country.

Laura Crook

Laura Crook is a research technician at Rothamsted Research, Hertfordshire, UK. She is a weed ecologist, whose research interests include herbicide resistance in Black-grass. You can find her on Twitter under the handle @crook_laura. The BGRI has a website at http://bgri.info/