Changing weather and soil conditions this autumn have led to stark differences in black-grass control between early- and late-drilled crops. Where black-grass counts are high, spring cropping might be a good choice to control populations.
“This year, fortune favours the brave,” says NIAB weed management specialist, John Cussans. “Conditions have changed dramatically within the season and it shows; the difference between black-grass levels in early- and late-drilled crops is remarkable.
“It was very warm and dry at the start of the season. Mid-autumn we started to get some rain and by the end of October, conditions were near-perfect in most places. Those that delayed drilling were able to spray off the late flush of black-grass and benefit from the wetter, colder soils optimising pre-emergence herbicide performance.
“Later drilled crops are looking remarkably clean. Early drilled wheat however, is not,” he observes.
Bayer commercial technical manager Darren Adkins agrees. “It’s amazing the difference just two weeks have made. Early sown winter wheat hasn’t got ‘high’ black-grass populations as such, but in many cases there’s certainly more than you’d like.” In early-drilled crop trials he reports an average of 10 black-grass plants/m2. “It’s not high but it’s still too high for long term population reduction.
“Growers in this situation now face the awkward decision of what to do next. Spray off and a spring crop? Or try and get a contact post-emergence herbicide like Monolith (mesosulfuron + propoxycarbazone) on in the spring?”
It’s a decision that Yorkshire farmer, Matthew Copley, had to take on his 263ha farm. With medium-heavy soils late drilling can be a challenge but this year, conditions were ideal for stale seedbeds and good pre-emergence herbicide applications.
“There’s just one field that has some heavy black-grass patches. Last year we introduced spring barley into that field’s rotation. Had we tried to continue with winter cropping alone, we’d have ended up in a right mess!”
Mr Copley applied Avadex (tri-allate) to the spring barley last year. “While it didn’t remove 100 per cent of the black-grass it did enough together with the cultural controls. Most of the control came from the spring cropping itself – the field was ploughed in late autumn, had a flush of black-grass in spring, then we were able to drill the spring barley.”
Mr Copley takes a flexible approach to rotations, reacting to black-grass populations on a field-by-field basis. “I’d like to return to winter cropping but whether we will depends on how the black-grass population reacts.”
Ben Stroud, a mixed dairy and arable farmer from the East Midlands, also uses crop rotations to manage black-grass. He describes the introduction of grass leys and spring crops as the ‘turning point’ on his 222ha farm.
“The moderate black-grass pressure is now manageable. In 2014 we had some fields that we couldn’t put a winter crop in. Now, the population is decreasing year-on-year. “The first big change involved making the most of the mixed farming. We started rotating the arable land with forage crops, using short-term leys – either a two-year grass ley or three-year lucerne ley. We’re putting combinable crops into our grassland too.”
Barley is Mr Stroud’s spring crop of choice. “It does well on the heavy land,” he says. “Although last year it didn’t go in until the beginning of May. It was just too wet to get it in any sooner after the very wet spring. You really do have to wait for the right conditions.”
The spring barley harvested completely clean and Mr Stroud didn’t use any black-grass herbicide. He just used an SU to take out broad-leaved weeds post-emergence. “This year some spring barley will go into cover crops – they are helpful, seem to suppress the black-grass and reduce the burden in the following crop – and some is going straight into stubble after failed OSR due to the dry autumn.”
For strong establishment in the spring Mr Stroud emphasises the importance of the right seedbed conditions and a robust seed rate (450–500 seed/m2). “It’s better to drill later when the majority of the black-grass has emerged,” he notes. Mr Stroud isn’t planning any autumn post-emergence herbicide on his winter wheat. Delaying drilling until the last week of October followed by a robust pre-em has left fields looking really clean.
Mr Copley will be applying Atlantis (mesosulfuron and iodosulfuron) plus pendimethalin post-emergence. When making spring applications he recommends spraying as early as possible. “As long as the black-grass is awake, we’ve had good results. You have to go early, as once the black-grass is beyond two leaf stage, it’s very hard to get the level of control.”
John Cussans agrees, adding; “As early as possible yes but for ALS herbicides (including Atlantis) active growth of the weed is critical – a week with overnight air temperatures over 4ºC will be enough to stimulate grass growth.”
Being ready to go in spring is key to delivering successful post-emergence treatments. “Early spring spray days are so short,” observes Mr Copley. “Contact herbicides need a drying leaf so you might only get 2–3 hours of optimum conditions, before night-time dew starts to form.”
“Good spray days are so few and far between that it’s important to be thinking and preparing for them now so you’re ready to go as soon as the opportunity arises,” adds Mr Adkins.