Consider the target weed spectrum, the weather forecast and the likely cost before finalising pre-emergence herbicide programmes for winter cereals, growers are being advised.

There are now 13 active ingredients with seven different modes of action that farmers can use at the pre-emergence and early post-emergence timing against weeds.

See also: How to maximise the benefits of stale seed-beds

While final choice will depend on the weed species expected to be present, the profitability squeeze that most cereal growers are facing will also be a relevant factor this year – especially as prices for some active ingredients vary widely.

This season is also the last chance to use up remaining stocks of Crystal (flufenacet + pendimethalin), after sales of the product ended.

With regards to spend, there’s no doubt that the pre-emergence timing has become the most important stage of the year in terms of weed control results, says Richard Hull, weed researcher at Rothamsted Research.

“It’s the best opportunity to get on top of grassweeds,” he stresses. “It’s the reason why there’s been a shift in focus of where herbicides are used in the rotation.”

Knowing what weeds are present, where they are on the farm and the location of weed seeds in the soil profile are important, as they are all factors which affect what action is taken, notes Richard.

Duration

One of the main requirements from the early spray timings is protection for over six weeks, so that weeds that continue germinating in warmer winter conditions are controlled.

The active ingredients chosen should be put together for that duration, as well as for their activity on the key weeds – with glyphosate being important too, either to clean up seed-beds beforehand or as part of the pre-emergence mix.

Follow up post-emergence sprays are always at risk from a change in the weather and are less effective, point out agronomists, who add that some pre-emergence products can also be undone by heavy rainfall.

© Blackthorn Arable

In that situation, a minimum seed depth of 3cm matters, they agree, reminding growers to follow manufacturers advice at drilling to prevent any unintentional crop damage from root uptake.

As a rule of thumb, flufenacet, metribuzin and cinmethylin are more soluble, moving through the soil for uptake by the roots, while aclonifen, pendimethalin and diflufenican are less mobile and can be taken up as shoots emerge.

Otherwise, industry-wide advice to stack and sequence products, mix modes of action and use the strongest materials available remains in place for autumn 2025, as does the need to use cultural control methods wherever possible.

Strong start

Starting with a strong approach for grass weeds is important, as all active ingredients degrade more quickly in warm and moist conditions and that well-timed sequences have the edge over an all-in-one approach.    

While flufenacet-based strategies were the mainstay at this timing and continue to be popular, the arrival of cinmethylin (Luxinam Plus) has raised the bar where both blackgrass and ryegrass exist.

With very good activity on both weeds, seed depth with the product is critical – especially if drilling is taking place later in the year in wetter conditions.

Where flufenacet mixes are favoured, the addition of aclonifen (Proclus) will boost pre-emergence performance, while the use of Avadex (tri-allate) before weed germinate brings synergy and an additional mode of action.

New addition

Joining the list of products available his year is FMC’s long-awaited Fundatis, a co-formulated herbicide that combines two new active ingredients – one of which brings a new mode of action to the UK.

Discovered and developed by FMC, the active ingredient is question is Isoflex (bixlozone), which belongs to the isoxazolidine family and works by inhibiting carotenoid biosynthesis.

In Fundatis, it has been partnered with beflubutamid, adding to the broad range of weeds controlled and giving it timing flexibility in wheat.

Containing 200g/litre of bixlozone and 125g/litre of beflubutamid, uptake of Fundatis is via the roots and shoots of emerging weeds.

As Gareth Jones, UK technical leader at FMC explains, the loss of active ingredients to resistance and regulation uncertainty is starting to affect pre-emergence chemistry, so having a new mode of action is to be welcomed.

Resistance strategy

“From an integrated weed management perspective, Fundatis arrives with a big tick in the box,” he says.

Trials with it conducted against resistant populations of blackgrass and ryegrass have shown no impact on the herbicide’s performance, he reveals.

“We are not positioning Fundatis as a one-can solution, especially when it comes to grassweeds,” he stresses. “Although it is widely available, its use on-farm will depend on the individual situation.”

Where broad-leaved weeds and annual meadow grass are the main threats, Fundatis can be the foundation of the herbicide programme, he continues.

“But if the main target is grassweeds, then it will be part of the stack, either in a tank mix or a sequence.” 

In winter barley, where it can only be used pre-emergence, there are fewer chemical options available so it will find favour, he predicts.