Plant Records: Big Problem. Big Experiments. Big Data.

Name: Black-grass
Scientific name: Alopecurus myosuroides
Known for: reducing yield and farm profitability; side effects may include hair loss, headaches and short finger nails
Record broken: being the subject of record-breaking Rothamsted Research efforts

How do you attempt to solve the biggest problem affecting arable farms in the UK? By conducting the biggest experiments, of course!! For Plant Records Week, I decided to focus on one aspect of our work here at Rothamsted Research, UK: As part of the Black-Grass Resistance Initiative (BGRI), we set out to investigate the level of herbicide resistance in black-grass populations in the UK. This became a major undertaking back in 2014. Earlier this year, I was given the opportunity to present our research at the Global Herbicide Resistance Challenge conference in Denver, USA. Here are five record numbers from our big experiment.

Record #1: One Big Problem

Black-grass (Alopecurus myosuroides) is a pernicious grass weed that affects arable crops, particularly winter wheat. The species gets its name from the dark coloured seed heads produced. It is very noticeable in June/July when the plants, which grow taller than the crop, appear as dark patches across fields. The problem with black-grass is that it is a very competitive weed, especially in fields of winter wheat. It germinates predominantly in the autumn, when the crop has also recently been planted. The other issue is that this species has evolved resistance to the herbicides that farmers use to control it. It is estimated that most of the 20,000 farms across England that regularly use chemicals to control black-grass, have herbicide resistant plants on them. If uncontrolled, this can cause up to a 20-30% yield loss. No wonder that UK farmers, when asked about the biggest problem facing them, name black-grass as problem number one.

Record #2: 70 Farms

There is a strong correlation between the presence of black-grass and the major wheat growing areas of England; namely the central and eastern counties. Therefore, any investigation into the levels of resistance present in these regions required representative samples from across these areas and with varying levels of infestation. Obtaining a network of farms to visit was our first challenge. We reached our target of 70 through using farms that had been used in previous weed research, putting an advert in the farming press, contacts through agronomists and, most successfully, standing at the Cereals agricultural show and accosting unsuspecting farmers as they walked past. Our network of farms stretches from Oxfordshire and Bedfordshire across to Norfolk and Lincolnshire, before finishing in Yorkshire, where the problem is less prevalent and therefore providing potentially useful samples for comparison. All of these farms have remained part of the BGRI project since 2014, having samples collected and being visited on a yearly basis to map the black-grass density patches across the fields.

Record #3: 132 Populations

Four Rothamsted colleagues spent six weeks over the summer of 2014 travelling the country to collect samples of black-grass from fields of winter wheat at the 70 farms in our network. I had only joined Rothamsted a few weeks earlier. We certainly got to know each other better during those busy weeks! I can still picture my colleague wringing water from his socks after we got caught in a downpour in the middle of a field; we’d decided the weather had looked ok and not put waterproofs on! The seed collection involved walking the tramlines of the fields and shaking handfuls of seed heads into bags. All of these populations were then brought back to Rothamsted. Each one had to be cleaned, weighed and labelled ready for use in our experiments. In total we had collected 132 populations.

60,000 Plants

Over the space of several months we screened approximately 60,000 individual black-grass plants with four different herbicides – we don’t do small experiments at Rothamsted. For each experiment, it took several colleagues three days to sow and place all the pots into their randomisation in glasshouse compartments. To spray with the doses of the herbicides requires muscle to carry all the trays of plants through to our pesticide sprayer. It then takes a few days followed by subsequent weeks to harvest, then weigh the dried plant material. All this work certainly improves your daily step count. And then of course, once the experiment has finished, the glasshouses require clearing out ready to start again.

Record #5: 77% Resistance

Analysis of all the thousands of plants screened as part of the experiments found that for the main herbicide used in the UK for control of black-grass, 77% of individual plants were resistant to field application rates. This poses a significant problem for farmers, as it is apparent that the chemicals are no longer working on some farms, and that their reliance is more on non-chemical methods of control such as delaying the time of drilling the crop, planting more competitive crops such as barley or moving to planting the crops in the spring instead. From the 132 populations, only two remained susceptible to all the herbicides tested.

The Global Herbicide Resistance Challenge conference in Denver brought together researchers from all over the world. My poster attracted delegates keen to learn what black-grass is, and how we managed to build up a network of farms to monitor. Many expressed amazement at the sheer scale of our experiments.

This experiment has been one of several conducted as part of the BGRI project at Rothamsted Research. Our aim is to gain a better understanding of black-grass, and trying to find the mechanisms that underpin its herbicide resistance. Screening all the 132 populations was a vital first step in cataloguing the level of resistance present in UK wheat fields, and providing an important resource that has been used in subsequent experiments. We hope that our research will assist in the battle against black-grass.

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/