Blackgrass is a weed that troubles many, and controlling it is an increasing challenge, particularly with the small armoury of products available, and the growing issue with resistance.
Paul Drinkwater, Crop Production Manager for Abbots Ripton Farming Company, explains how, in his 40 years of being in the Cambridgeshire area, the blackgrass problem has evolved.
“My role sees me manage 3,600 hectares across north-west Cambridgeshire. The land is owned by Lord de Ramsey, but I’m responsible for the agronomic decisions and agronomy for all the farmland on the estate, and work closely with two farm managers, who carry out the day-to-day operations.
“Due to the expanse of the land we cover, we’re farming two distinctly different land types. At Abbots Ripton for example, the soils are heavy, boulder clays and so are more suitable for combinable crops.
“Typically, the rotation consists of two wheats, followed by either oilseed rape or beans. The rest is generally fenland which means we can grow potatoes, as well as other root crops and legumes,” says Mr Drinkwater.
He explains that they’ve always had blackgrass issues, but the difference in the last couple of years is the loss of efficacy of post-emergence chemistry which has meant they’ve struggled to control the weed.
The blackgrass challenge
“This season has been an even greater challenge for us, and it appears everyone is saying the same thing,” he explains.
“When I walked the plots back in the spring, it was clear the pre-emergence herbicides had done their job. There was still a couple of blackgrass plants per square meter, but at the time this didn’t seem so bad.
“However, these plants went onto have at least 20 tillers each, and ears as big as your finger. As a result the seed return this autumn has the potential to be enormous.”
One theory behind the bigger plants relates to the mild winter, allowing the remaining blackgrass plants to continue to grow. The cool, damp spring then encouraged blackgrass plants to tiller and produce more seed heads.
“This meant that when we could finally get onto the fields for post-emergence sprays, the blackgrass plants were too big to control,” he adds.
“Plants with bigger tillers, is another thing that we are seeing more of. Five years ago, plants would only of had two or three tillers each, but now they are regularly having over 20. This is potentially because we’ve selected for the most vigorous plants.
“You could say we’re a victim of our own actions,” he says.
Control this autumn
Mr Drinkwater explains that this autumn, stale seed beds need to be a priority, due to the potential enormity of seed return levels. “Cultural controls are key to what we do here, and are vital for managing blackgrass populations.
“A stale seed bed allows as much blackgrass to grow as possible so we can kill as much off in the initial stages, prior to drilling.
“However, the key is, once you’ve created the stale seed bed, don’t disturb it again, which can be a challenge, but this reduces the risk of uncovering any fresh blackgrass seeds that could come up with the crop.”
Once drilled, Mr Drinkwater will spray with a pre-emergence herbicide within 24 hours. “There is no doubt that flufenacet is an excellent pre-emergence herbicide.
“We’ve had great success with Certis’ straight flufenacet product, Sunfire, as a pre-emergence herbicide. And, the fact you can add your own partner chemical is a real benefit.
“Our best tank mix has come from mixing Sunfire, with prosulfocarb and diflufenican. Every on-farm situation is different, but flufenacet has got to be the backbone of an effective pre-emergence spray programme.”
He explains that the aim is to get the crop established and out-competing what blackgrass there is. “Post-emergence control is currently a problem for us, as this type of chemistry is losing efficacy due to resistance, so we need to get a good level of control as soon as possible.
“At best, I aim for 40% control post-emergence, but often it’s less than this. Very often what blackgrass we are left with, we can’t control, so it’s likely to be left through to harvest, which can have a significant impact on yields.
“In the past, if we’ve had really bad blackgrass we will spray off the area at any stage of the season, and have even been known to take out whole fields when the plants have been too big to control.
“Blackgrass is a challenge and one that there is no quick solution to. But, the more we can use an integrated approach that utilises cultural controls and effective pre-emergence chemistry responsibly, the better level of population control we will achieve,” says Mr Drinkwater.