While many are having success so far this year in the battle with black-grass, completing herbicide programmes and removing survivors is the key to winning the war.
A dry autumn had some farmers and agronomists worrying about pre-emergence performance, but a combination of delayed drilling and late autumn rain brought black-grass flushes just in time for residual herbicides.
“We’ve seen good control this year so far,” observes independent agronomist Sam Clarke. Working across Oxfordshire, Warwickshire, Leicestershire and Northamptonshire, Mr Clarke advises on land with a wide variety of soil types with varying black-grass pressure. “On the whole, growers had prepared by prioritising the worst black-grass for later drilling and established stale seedbeds.”
That was the case for Leicestershire farmer, Chris Tolley. “I wouldn’t say we’re on top of the black-grass but we’re trying. We use a mixture of cultural controls, pre-emergence herbicides but also post-emergence and spring cropping where necessary,” he says.
“We always aim for autumn post-emergence herbicide applications but where we have to go in spring, we wait for a warm spell, when weeds are actively growing, and we can travel without causing damage. We try to do that as soon as possible before the black-grass gets too big – once it has several tillers, control will certainly be compromised.”
Mr Clarke agrees. “Active growth is related to soil temperature,” he explains. “The bottom of hedgerows starting to green up is a good indicator, but I also keep an eye on diurnal temperatures. If it’s 10oC during the day and 6oC at night, then it won’t be long before soil temperatures rise to 6oC – the temperature when black-grass will start moving. It’s harder to judge when there’s frost at night but it’s warm during the day. That’s when I use a digital thermometer at the rooting zone. I’ll pop it in the soil about 4–6in deep, walk the fields and come back to take a reading.”
Where black-grass is susceptible to ALS chemistry, Mr Clarke mainly advises autumnal use of Atlantis (mesosulfuron + iodosulfuron), provided conditions are good. This year he’s only seen a handful of fields requiring spring applications, predominantly on heavier later-drilled land where the black-grass didn’t emerge in time for an autumn post-emergence. On these sites he is likely to use Monolith (mesosulfuron + propoxycarbazone).
“Monolith is another weapon in the arsenal for spring contact chemistry, which is just what is needed on some farms,” he says. “But we have to use these new products responsibly – and the first step is resistance testing, which Bayer has provided help with. Where there are weeds that are open to this type of chemistry, it’s definitely a good one to use.”
While Mr Clarke has only a handful of fields needing post-emergence treatments, he will be paying close attention to optimising efficacy with application technique. He encourages growers to follow the advice “time over target”, keeping forward speeds down to 10kph and using 120–150-litres/ha of water. He does not think there is any benefit in using 200-litres/ha or more because the focus should be on droplet size and spray quality rather than applying a high quantity of water.
Mr Tolley agrees. “Getting the spray quality right is important. Where possible we use a fine spray to get good coverage and hit the target. Travelling slowly and keeping the boom height at 50cm above target helps too. We always use a water conditioner because we have hard water here. Together with the appropriate adjuvant, Biopower, they help maintain efficacy.”
The other piece of advice from Mr Tolley is to be patient and wait for a dry leaf. Starting too early in the morning or finishing too late is a false economy as the herbicide won’t dry properly on the leaf. Although it shortens the spray day down to four or five hours you can be more confident that the herbicide is taking effect.
The post-emergence treatment doesn’t finish with making the spray – it is essential to check and eliminate any survivors to prevent resistance building in the population. May is typically the month for assessing overall weed control and making any final decisions to rogue and spray off. “At that point, we’d be considering removing those with glyphosate. Anywhere that contains a few plants that got away, we will hand rogue,” says Mr Tolley.
A sound decision, according to Mr Clarke. “While it seems madness to get that far and then potentially spray off a crop, it’s worth it. A black-grass population can get out of hand quickly as its seed return is huge; 100 viable seeds/tiller and you can easily get 20 tillers per plant. The future herbicide costs will far outweigh the lost margins this year.”