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Adjuvants hold the key to herbicide success

Using the right adjuvants could be key to ensuring herbicide efficacy this year, following the challenging weather for planting crops and applying herbicides.

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Adjuvants hold the key to herbicide success

Many growers will have been unable to plant winter crops or spray in autumn.

For some who are playing catch-up this spring, the only solution will be a big, complex tank mix.

Stuart Sutherland, technical manager with adjuvant specialist Interagro, says: “This autumn and winter have been the worst in living memory and we expect spring 2020 to see a significant shift in cropping choices as a result.

“Arable farmers have planted the smallest winter cropping area for decades following the relentless rain and flooding.

According to the AHDB planting survey, only 1.2 million hectares had been planted by mid-February, compared to a typical figure of 1.8m.” Stuart McDowall is an agronomist with Agrii, based in Lincolnshire.

For him poor, cloddy seedbeds and a lack of residual herbicide applications are among some of the biggest issues.

He says: “For me, black-grass is one of my biggest concerns.

Very little residual herbicides have gone on and now we also have the challenge of controlling spend on crops which may produce very moderate rewards.”

 

According to Mr Sutherland, many farmers will have been presented with one of three difficult situations: Lack of pre-emergence herbicide treatment will have led to more established, large vigorous overwintered weeds which could be harder to control.

Stuart Sutherland
Stuart Sutherland

Cropping

 

Inability to drill winter crops may mean unplanned spring cropping which has its own challenges.

Growers may have to play catch-up once conditions are more conducive to spraying and this could mean resorting to complex tank mixes.

For weeds which were not sprayed pre-emergence in autumn, there will be a big spring clean-up job to be done.

In addition to more vigorous and established weeds, black-grassinduced dormancy from seed sat in wet soils over winter may also increase the risk of higher germination in spring when soils dry out.

With herbicide resistance issues more commonplace in postemergence chemistry, weed control is likely to be more problematic and reducing weed populations to prevent seed return will be crucial for any effective anti-resistance strategy.

Mr Sutherland says: “Generally, good weed control post-emergence is dependent on well-timed sprays applied to small weeds in good conditions, but this is not going to be the case this year.

Large weeds are harder to control because spray coverage is difficult and a post-em contact herbicide needs contact across the leaf.

“Growers must be aware the use of low drift nozzles may help you get on, but it does reduce coverage and will not give adequate deposition on any fine vertical grass-weeds.

“Large weeds hardened over winter will also be more able to resist the herbicide, with a tough waxy cuticle which will make penetration more difficult, particularly herbicides which are moderate to high water soluble in nature, such as sulfonylureas and pinoxaden.”

Mr Sutherland is concerned about the lack of herbicides applied to black-grass this season.
Mr Sutherland is concerned about the lack of herbicides applied to black-grass this season.

Complex tank mixes

Inability to get onto fields during autumn and winter will have undoubtedly left many growers needing to catch up and one way of doing this is to use large, complex tank mixes.

Mr Sutherland says: “The danger with complex tank mixes is they are harder to dissolve, particularly in cold water.

This affects crop safety and reduces the availability of active ingredients.

Only those ingredients which are fully dissolved will be available.

“Kantor is a self-emulsifying compatibility aid which enables complex tank mix components to dissolve and remain thermodynamically stable.

Kantor will also reduce spray drift and improve disposition on the leaf.

Protection “It is compatible with common plant protection products and fertilisers and approved for more than 50 crops.” For Mr McDowall, it is the reduction in spray-drift which justifies the use of Kantor.

He says: “For me, it is an amazing product.

It reduces drift dramatically in a tank mix and, in situations where that tank mix is quite large, Kantor can help with availability.

If you’re spraying in catchy weather, it also appears to improve rainfastness.” This spring, Mr McDowall plans to use it at all timings to improve product retention and promote better uptake and activity.

He says: “With new chemistry coming forward, being able to squeeze another 5-10% out of the active during every application can only be a good thing for minimising resistance issues.”

Challenges

Sorrento is a new activator adjuvant designed to help optimise the performance of post-emergence herbicides and overcome challenging conditions.

It will help to ensure good coverage on more established weeds, provide exceptional binding to prevent run-off and delivers fast penetration into weeds.

Faster uptake will get the herbicide working faster.

One of the most noticeable benefits of Sorrento is the speed at which it works, with significant improvements in speed of kill seen in trials even by the first assessment.

Unplanned spring cropping could be a challenge, particularly where soils need remedial work ahead of drilling.

With the wet, warm autumn conditions, coupled with soil disturbance, growers should be prepared for potentially higher blackgrass germination than normal.

To be effective, residual herbicides require good coverage across the soil surface to ensure contact with all germinating weeds.

Cloddy seedbeds should therefore be minimised where possible to prevent further protracted emergence of weed seed.

Herbicide applications in suboptimal conditions could exacerbate the threat of germinating weeds getting missed.

In these conditions, ultra-fine spray droplets can drift off target, leading to poor coverage in some parts of the field, and weeds which do not come into contact with the herbicide at emergence will not be controlled.

According to Mr Sutherland, Interagro adjuvant Backrow can help reduce these risks by creating the ideal droplet size for pre- and periemergence applications.

He says: “Backrow reduces the number of fine spray droplets prone to drift and increases the number of spray droplets in the optimum size range for better coverage.

“Once applied, herbicides need to be activated to move from the soil surface to the weed root zone in the top 5cm of soil.

This is either done by rainfall, or by moisture in the soil, which certainly should be the case at present.

In order to reach the roots of the weeds, the herbicide has to move into the top 5cm and be retained there.

Crop injury

 

“There is also a danger that if the herbicide moves too much in the soil it will reach the crop roots and then there is a risk of crop injury.

“Backrow retains the herbicide in the top 5cm of soil, reducing the threat to crops and leaching to groundwater, increasing efficacy against weeds.

This could be crucial where using herbicides such as metazachlor, dimethenamid-P, imazamox, clomazone or flufenacet.

It will also be useful if protracted weed germination does occur.

“Should conditions miraculously dry up, this can also impact on the efficacy of herbicides, particularly those which have a tendency to bind to organic matter, such as pendimethalin, picolinafen or aclonifen.

In these conditions, Backrow can also help ensure effective application.” Mr McDowall is also advocating the use of Backrow.

He says: “I predominantly use it at pre-emergence, though will include it at peri-emergence if pushed to that stage.

“Backrow seems to create a protective barrier, so any spring – or late autumn weeds – have to push through that, meaning you definitely see an improvement in control.

Particularly in the case of laterseason broad-leaved weeds.”

Brought to you by Interagro

Brought to you by Interagro

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