Blackgrass control should take priority over broad-leaved weeds

Weed control plans thwarted by the weather will have to get back on track this spring if another bad blackgrass year is to be avoided, as Louise Impey finds out

Do what’s right for controlling the blackgrass first. The broad-leaved weeds can be tackled later.

That’s the advice for growers who know that blackgrass is likely to be a problem in their wheat crops, after difficulties getting pre- and post-emergence sprays completed.

Fears that growers will be forced to rely mainly on contact herbicides, with their well-documented falling efficacy and resistance risk, are being voiced by agronomists, who add that weed control problems could be compounded by late, less competitive crops.

Drilled, but not sprayed, is how AICC chairman and independent agronomist Mike Warner describes much of the winter wheat in his part of Suffolk.

“Blackgrass is there in numbers and it’s starting to tiller,” he says. “Very few crops received anything in the way of herbicides in the autumn, so there’s plenty of work to be done.”

He is hoping to use Atlantis plus the lower rate of Liberator towards the end of February, if conditions allow, on those crops. “I can’t see much point in trying to get just a residual on now. But application conditions will be very important for the Atlantis to work well.”

Where broad-leaved weeds such as cleavers are also expected to be present, Eagle can be included with Atlantis, he comments.

Others agree, pointing out that the efficacy of residual herbicides on blackgrass that has reached the two leaves stage is questionable.

“Control could be poor,” says David Parish of NIAB TAG. “If the first half if February is dry and cold, it might be worth doing. But if it’s mild, it would be better to go straight in with an Atlantis mix.”

Later drilled crops which received no pre-emergence treatment are his main concern. “The potential advantage of the later drilling date on blackgrass control has been offset by the fact that no residual was applied. If anything, these fields are in the worst situation of all.”

That’s because the wheat and the blackgrass germinated together, he notes. “And there’s hardly been any post-emergence spraying done. All the Atlantis-type treatments are still to take place.”

He also favours 0.3 litres/ha of Liberator plus Atlantis. “Deciding what you do put in with Atlantis depends on the weed spectrum present. There’s also an opportunity to add in some pendimethalin or to use a product such as Auxiliary.”

Mr Parish plans to give grass weeds the priority, opting to come back later for broad-leaved weeds.

For most, Atlantis is the preferred option on blackgrass as the weed gets bigger. But Unite can be used in the spring and should work well if the blackgrass is still small, they explain.

For Nick Wall in Hampshire, blackgrass is not a pressing concern. He estimates that 60% of crops received an effective pre-emergence spray. “The earlier wheats are all done. The pre-emergence has worked well and there’s very little blackgrass around.”

Both grass and broad-leaved weed levels are lower than usual in his area. “And where they are present in number, they’re smaller. Having a smaller plant to target, especially with grass weeds, is an advantage.”

Broadway Star will be used where sterile brome needs controlling, he adds. “I’ll be timing that application as normal.”

Atlantis advice

Using a high risk contact herbicide on its own this spring should be avoided where possible, advises Chris Cooksley of Bayer CropScience.

That’s why being able to include the lower rate of Liberator with Atlantis up until the end of March is so useful, he says.

“The situation in many fields is more like an autumn scenario than a spring one, which is why having a residual in there is a good strategy,” he says.

“Having a contact plus residual mix also means that where seed-beds are lumpy, any clods breaking open and releasing weed seeds won’t be a problem.”

He stresses that the land has got to dry out before any spraying can take place. “For many, that’s still a few weeks away.”

When spraying does resume, there are a few considerations, he adds.

“Crops will be quite soft, so the potential for crop damage is higher, especially if they’ve been stressed or waterlogged. The frosts will have helped and growers often report very good control from applications made after a cold snap.

“Furthermore, the blackgrass must be showing signs of active growth. Go by appearance rather than soil temperature.”

A dry target leaf is also required. “That can be quite a challenge with short day lengths, but it is important.”