Largest UK weed survey reveals Italian ryegrass challenge – Farmers Weekly


Results from the UK’s largest survey on Italian ryegrass has proven a posh and variable image of herbicide resistance within the weed, emphasising the necessity for growers to check and perceive the populations on their farms to attain higher management.

However, rising ranges of resistance to generally used herbicides usually are not the one reason for management difficulties, reveals weed specialist John Cussans of Niab, who additionally highlights utility timing and higher use of diversified modes of motion as essential actions.

See additionally: Tips on tackling 5 weed points in no-until methods

“There is scope to enhance follow, as there are too many hearth brigade therapies being made,” he advises.

“It’s an advanced panorama in terms of resistance mechanisms, however higher consideration to element will assist to keep away from poor choice-making.”

Conducted by Niab with funding from Bayer, the survey of 197 samples from throughout the nation investigated present on-farm management follow, in addition to testing every Italian ryegrass pattern for sensitivity to flufenacet, pinoxaden (Axial) and ALS herbicides (Atlantis).

In addition, 22 of the weed samples had been utilized in a cross-resistance research, to grasp any correlations between sensitivity to a variety of herbicides, together with glyphosate.

Post-emergence herbicides

“While the efficiency of submit-emergence herbicides is considerably affected by resistance, it was decrease than anticipated,” says Mr Cussans. (see “Post-emergence herbicide sensitivity”)

“The indisputable fact that a lot of samples are nonetheless vulnerable to herbicides goes towards the notion that many have about submit-emergence chemistry.”

Dropping using completely good herbicides tends to occur when the resistance menace is exaggerated, he explains, which is why a greater understanding of the scenario on particular person farms is so essential.

Pre-emergence herbicide

When it involves pre-emergence herbicides, all 197 samples had been examined for sensitivity to straight flufenacet.

One-third of them confirmed both decreased sensitivity or resistance, reflecting that the choice stress has been there for a while.

“If you pile on flufenacet, you’ll choose resistance to it,” he says. “Of course, in follow it isn’t used alone – it’s tank-combined and sequenced with different actives.”

There are some populations of Italian ryegrass which can be fully proof against flufenacet – which makes it completely different to the scenario with blackgrass, the place there was a shift in sensitivity, reasonably than full failure.

Post-emergence herbicide sensitivity (% of samples)

Atlantis   Axial
S 45.6 45.6
R 7.7 6.2
RR 24.1 32.3
RRR 22.6 15.9

Pre-mergence herbicide sensitivity (% of samples)

Sensitive 70.6
Significantly Reduced 17.3
No Control 9.6

Resistance testing

Further evaluation confirmed regional variations between the three herbicides examined, with management from flufenacet being decrease within the South East, North and Midlands.

“If you have got an rising situation with pre-emergence herbicides, you should learn about it. Get resistance testing performed, ideally on a discipline-by-discipline foundation – nationwide statistics will make no distinction to managing your weed populations.”

Even populations collected from two fields on the identical farm can present variations in herbicide sensitivity, he warns, reflecting the very variable herbicide sensitivity current across the nation.

Cross-resistance findings

A subset of twenty-two populations was used to check extra herbicides and perceive any correlations between them, in addition to to have a look at glyphosate sensitivity.

The strongest correlation is between the present pre-emergence actives – flufenacet, pendimthalin and prosulfocarb – whereas aclonifen is weakly correlated with sensitivity to present pre-emergence merchandise.

“If you have got flufenacet resistance on the farm, you should usher in different modes of motion,” advises Mr Cussans. “Where three actives are mixed, similar to Liberator + Proclus, it largely overcomes flufenacet resistance.

“Broadening the bottom by combining modes of motion helps to stabilise ryegrass management. That indisputable fact that we have now two new modes of motion this yr in aclonifen and cinmethylin, and one other coming subsequent yr, will assist.”

Having a stronger, extra various base for Italian ryegrass management is essential, he stresses.

“Ryegrass is extra able to overcoming herbicides and we all know there’s a diploma of cross-resistance between present pre-emergence chemistry.

“For this motive, it’s essential to mix modes of motion.”

Glyphosate sensitivity

There has been a shift in sensitivity to glyphosate in some problematic UK Italian ryegrass populations, however it’s not resistance, confirms John Cussans.

The standing of fifty troublesome weed populations collected in 2019 was checked for his or her sensitivity to glyphosate at a variety of doses, with some variation exhibiting.

“We should not have glyphosate resistance within the UK, however we’re as shut as we’ve ever been to it,” he cautions. “That’s why we should monitor it and steward the product.”

Glyphosate sensitivity is completely unbiased of in-crop herbicide use, with the correlation between glyphosate sensitivity and sensitivity to different herbicides being very poor.

However, there is no such thing as a doubt in Mr Cussan’s thoughts that poor follow will result in glyphosate resistance, because it has been attainable to pick for glyphosate resistance in excessive-danger situations in glasshouse work.

“We should keep away from any survivors of glyphosate purposes happening to set seed.”

As a consequence, growers should take possession of this situation and observe printed steerage, he advises.

That is a view shared by Roger Bradbury, technical specialist at Bayer, who stresses the necessity to apply glyphosate on the proper time, with the proper dose for the goal weed and with good utility approach.

He refers growers to the newest Weed Resistance Action Group tips, which suggest a most of two glyphosate purposes after harvest, earlier than drilling the subsequent crop, and stress the significance of monitoring herbicide efficiency and investigating any causes for poor management.

“Everyone wants to pay attention to the dangers and do all they’ll to stop resistance to selective herbicides.”

Aclonifen approval in barley

Bayer’s Proclus (aclonifen) has been authorised in a tank-combine with Liberator (flufenacet +  diflufenican) for pre-emergence weed management in winter barley, including a brand new mode of motion and increasing the choices for grassweed management within the crop.

A decrease utility fee of 1 litre/ha + 0.6 litre/ha Liberator, in contrast with 1.4 litres/ha in winter wheat, means the degrees of weed management are barely much less – with a 7% uplift in Italian ryegrass recorded in Bayer trials and a 5-6% enchancment in blackgrass management.

Winter barley’s earlier drilling date and extra restricted herbicide selection could make it a difficult crop for weeds, says Bayer’s Tom Chillcott, who factors out that together with aclonifen within the pre-emergence combine offers extra safety and helps with resistance administration.

“Having a brand new mode of motion in barley provides one other layer of safety and helps to take the choice stress off flufenacet.”

As aclonifen sits on the soil floor, weeds need to develop up by it earlier than it takes impact, he provides.

“That means seed-mattress preparation, drilling depth and utility timing all matter, particularly as aclonifen generally is a bit scorching in some situations, and barley is a extra delicate crop.”

A minimal sowing depth of three.2cm and utility inside 48 hours are essential, as is avoiding heavy rain quickly after utility.

It might be offered as a co-pack of Proclus and Liberator, as in wheat, and can add £10/ha to pre-emergence prices in barley.


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