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07 Sep 2021

New tools strengthen the case for IWM principles

As featured in Arable Farming Magazine

New tools strengthen the case for IWM principles

by Arable Farming September 2021

How much are farmers implementing integrated weed management principles and what new tactics are being developed? Mike Abram reports.

It might be somewhat by default, but uptake of integrated weed management (IWM) principles is higher than the equivalent integrated approaches to controlling pests and diseases.

But some new tools are being developed that could play an important role in future strategies, as more attention is paid to integrated weed and pest management driven by reducing availability of herbicides and their effectiveness.

At its heart, IWM is about using multiple methods of controlling weeds, rather than relying on just one alone. That can be a combination of cultural, genetic, mechanical, biological, as well as chemical controls.


Relying on just one tactic usually chemical has proven to be counter-productive, for example in controlling black-grass.

Dr Sarah Cook, senior weed biology research consultant for ADAS, says: Black-grass has driven farmers to use integrated weed management, sometimes without really realising it.

Resistance and the loss/lack of chemicals has driven the greater uptake, she adds.

In comparison, there are a lot of effective fungicide options, with new ones arriving so there is less IPM in the disease sector because they havent been driven to take it up.

Proactive uptake of IWM has not really happened. A 2019 Research Review published by AHDB ‘Weed control options and future opportunities for UK crops identified barriers to uptake including little visible evidence of immediate success and little idea of the return on investment in time and money. But the key one is that herbicides, as the report says, usually cheaper and take less time to apply.

It appears that non-chemical practices are often only adopted to compensate for reduced herbicide efficiency, says Dr Cook.

Among the key recommendations in the report was for a more strategic approach to weed control across rotations than the current approach, which is often based on the use of herbicides against specific weeds and/or in specific crops.

There is no shortage of potential weed control tactics for growers to use the report highlighted more than 50 options.


Understanding how to employ these different weed control tactics in a smarter, more efficient way across rotations is a key target for scientists, says Richard Hull, a weed ecologist for Rothamsted Research.

Rothamsted and NIAB are just two of 37 partners across eight European countries involved in the €6.6 million EU-funded Horizon 2020 IWM Praise project which aims to do just that. Through a series of work packages, it aims to look at why farmers either do or do not adopt current IWM tactics, research new techniques (see panel, p43), and assess the long-term agronomic, environmental and economic impact of IWM strategies.

Mr Hull says: Hopefully this project will make a difference in the next few years.

He adds there are two key principles when developing an integrated weed management plan.

Firstly, you need to know what your target species are their life cycles, germination periods and what the strengths and weaknesses are that you can get on top of, to help understand what tactics can be used to reduce the burden of those weed species.

The second major factor is the time and resources and capability of implementing these tactics. There may be limiting factors that mean you cant employ everything you want to do, but auditing what you are doing will give you a good idea of what you can do in the future within the limitations you have.

He splits integrated weed management tactics into four areas: cultural, mechanical, chemical and prevention.

Good IWM starts with rotation, having a diverse range of crops, and leading from that a range of drilling dates.

Drilling date is an example where that knowledge of weed biology helps, he says.

By altering drilling date, you will either favour the weed, or your chances of controlling it. For instance, knowing which of the two species of wild oats you predominantly have on your land; if it is avena sterilis, which mostly germinates in autumn, then spring cropping can reduce the weed burden considerably.

Broad-leaved weeds

While drilling date is an important factor for many grass-weeds and IWM tends to be focused on dealing with pernicious grass-weeds it is less important for broad-leaved weeds, where germination tends to be more protracted, he adds.

Tillage also doesnt work quite so well to reduce the seed bank, as generally broad-leaved weed seeds are smaller and have much longer persistence in the soil.

If cultural control is number one, second on his list is mechanical control.

So the use of soil movement and tillage. Im not getting into a debate about which is better, but both have a place within a rotation, and again, having diversity in your system.

If and when you plough, make sure youre doing it to the best it can be done and then for most grass-weeds in the intervening years no-tillage or moving as little soil as possible is the best option, so youre not tapping into that seed layer you ploughed down. You only get one chance every three to four years to hit the reset button.

Other forms of mechanical control are starting to become potential options, such as harvest weed seed control and inter-row hoeing (see panel, right), he says.

They are becoming more prevalent as the reliability of machines with GPS increases and costs come down.

While IWM is aimed at reducing the reliance on chemical control, herbicides still play a vital role in controlling troublesome weeds, Mr Hull says.

Its still the number one tactic growers are going to use. Its completely understandable as it is the most reliable form of control.

All the non-chemical control tactics have inherently more risk as there is a higher level of variability in control, so herbicides are likely to play as vital a role over the next 10-20 years as they have over the last few decades. to consider is prevention.

Prevention is making sure you know what is coming on to your farm, so you are not getting any ingress of new species into your fields.

Pulling that altogether as many farmers are already doing for key grass-weeds will give the best chance of sustainable weed control. However, an area

that is perhaps overlooked is monitoring fields for success, he says.

Farmers are employing a suite of tactics, but Im not sure they always know exactly what the outcome of employing them is.

Negative effect

It might be that farmers are employing tactics that could be having a negative effect rather than the positive effect they think they are having, so monitoring how well these tactics are working is key for long-term weed control.

A new Defra-funded project, led by ADAS and commissioned by AHDB, is reviewing various integrated pest management tactics and scoring them against different criteria, such as effectiveness, cost, ease of implementation and speed of impact, Dr Cook adds.

The aim of the project is to identify how to increase adoption of the most valuable interventions.

How mechanical options might help future weed control

NIAB trials manager Will Smith has been researching how interrow hoeing and harvest weed seed management could fit into UK weed control programmes as

part of the IWM Praise project and his PhD studies.

A Garford Robocrop guided hoe, predominantly used in horticulture, is being investigated for black-grass control in winter wheat, with and without herbicides.

So far it has not proven to be as effective in this situation as in other countries, with timing a challenge on heavier soils that can be either too wet or too dry.

But it still gives an uplift in control of around 15-20% when used in combination with herbicides. That could be valuable, particularly in years when pre-emergence herbicide effectiveness has been lower because of dry weather, for example, he says.

Spring-germinating weeds, such as wild oats and some bromes might be a slightly easier target when timing could be more flexible for where soils are drier, he adds.


Another possibility NIAB is investigating is combining inter-row hoeing with in-row herbicides.

With that system youre able to reduce your herbicide loading by 60%, with the same weed control effectiveness as a broadacre herbicide.

Mr Smith has also been trialling a couple of harvest weed seed management machines. Zurns Top Cut Collect, commercially available to buy in the UK, cuts the

tops off weed plants preharvest and collects the seeds in a bin for disposal.

This season it has been used against black-grass and brome.

For black-grass, getting the timing right is imperative as seed shed can start quite early. Later maturing weeds like brome and ryegrass may be better targets as

they enable greater flexibility, says Mr Smith.

Ryegrass and brome could also be prime targets for combine-attached seed mills, such as the Canadian firms Redekop mill being trialled by NIAB.

The mill takes the chaff and mills it up to fine dust with a set of rotors that it throws out with the straw.

In other parts of the world this technology has proved incredibly effective, however it relies on getting the seeds into the combine which is what we are evaluating, Mr Smith adds.

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