Blackgrass© Tim Scrivener

A new post-emergence herbicide for spring use on winter wheat is set to offer 10% better control of blackgrass than its predecessor, Atlantis, enough to turn the tide on blackgrass infestations.

Monolith from Bayer is being positioned as a specialist grassweed herbicide, which could give a 0.3t/ha yield benefit – equating to £42/ha – compared with Atlantis.

The group has removed the broad-leaved weed herbicide iodosulfuron from Atlantis and added propoxycarbozone, a second blackgrass active.

See also: New herbicide offers fresh blackgrass control option

This change, coupled with an increased amount of mesosulfuron, has improved blackgrass control over Atlantis by an average of 10% in 19 independent trials.

More consistent

The new herbicide also performs more consistently, meaning a grower who saw only a 16% control of blackgrass with Atlantis could potentially achieve 53% with Monolith, says Bayer.

Ben Coombs, the group’s cereals herbicide manager, said that in the trials Atlantis offered between 16% and 94% control, while for Monolith the range is just 53% to 95%.

He added that broad-leaved weed populations are declining because of good stacks of residual herbicide, putting the focus for growers on controlling blackgrass.

However, he said that one area where Monolith has proved less effective – as a result of the removal of iodosulfuron – is on tackling resistant strains of Italian ryegrass.

Early application

Mr Coombs recommended that the new product should follow an autumn programme of cultural controls for blackgrass and pre-emergence treatments, such as Bayer’s Liberator (diflufenican and flufenacet).

He said that the new herbicide should be applied as soon as conditions allow from 1 February to mid-April, or between GS21 and GS32.

This will allow the chemical to be taken in by the leaves while there is active growth, leaving the flexibility for growers to choose broad-leaved weed controls to match their specific needs to mix with a T1 or T2 fungicide spray.

Mr Coombs said that in practice the key application window for the herbicide is likely to be March, and growers should not look to tether their broad-leaved weed control or fungicide applications with their blackgrass programme.

“Ideally, farmers wouldn’t try to combine passes; those are days we shouldn’t try and go back to. Apply Monolith as soon as possible and then move on to broad-leaved weeds and fungicide,” he said.

Reducing the seed bank

A key yardstick in the control of blackgrass is the number of seeds returned to the soil seed bank, said Dr Harry Strek, scientific director of weed resistance at Bayer’s Weed Resistance Competence Centre.

Using Monolith over Atlantis would result in 28 fewer heads per sq metre remaining, resulting in 28m fewer seeds being returned to the seed bank.

Controlling this seed bank is key to reducing blackgrass infestations, said Dr Strek, and the difference between blackgrass being maintained at a consistent level or spiralling out of control can be just 2% control.

Putting it into decline can be as little as a 10% difference, meaning Monolith has the potential to provide a step-change in the battle against blackgrass. However, he added that while chemical control is important, the number of spring crops grown in a rotation is the number one factor for blackgrass control.

He said that more economic information needs to be developed locally to inform growers of the benefit of an integrated weed programme, but added that a French study that used an integrated programme of herbicides, stale seedbeds and spring crops such as maize showed this system can pay dividends.

Under this system, every £1 spent on the integrated approach would pay back £3 in yield.

Bayer said that Atlantis will continue to be available for next spring.