Since its launch in 1974, Roundup has been first choice for non-selective chemical weed control for farmers across the world. Used for controlling weeds in stubbles and stale seedbeds, patch control of noxious weeds, harvest management and grassland reseeding, Roundup and its active substance glyphosate is remarkably versatile and effective. It is relatively simple to use but don’t let that be a reason for complacency, ensure you optimise performance and prevent resistance with effective product stewardship.
Mode of Action
Once applied to the leaf uptake occurs within 1-6 hours and glyphosate moves through the phloem both downwards and upwards within 5 days. It tends to accumulate in the growing points, then evens up throughout the plant, leading to a gradual loss of green colour followed by death between one and four weeks later.
Glyphosate works at a single specific site in the Shikimic acid pathway to inhibit the production of the amino-acids phenylalanine, tryptophan and tyrosine. Amino- acids are the building blocks of protein molecules and once the biochemical pathway is blocked the synthesis of proteins is interrupted and the plant effectively starves to death. The process is temperature related and explains why treated plants take some time to die.
All agrochemicals need particular weather conditions, good application technique and target weeds in a receptive condition to achieve the best results. Factors affecting the performance of Roundup are detailed in this section to help achieve the very best results every time it is used.
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The Importance of Statutory Conditions and Fields of use Within the Law
Everyone who uses pesticides referred to as Plant Protection Products, (PPP) should abide by the Code of Practice for using plant Protection Products 2006 (COP). It has legal status and by following the advice you will be within the law. Both The Food and Environment Protection Act 1985, (FEPA) and the Health and Safety at Work Act, 1974 apply to the use of PPP.
David Lord is nearly a decade into a regen farming approach with cover crops and direct drilling contributing to healthier, more resilient soils. Farming in Essex, he has avoided the worst of the bad weather, but his farming system has helped mitigate some of the risks.
“We do as little cultivation as needed. On the better drained land we haven’t needed to cultivate for eight or nine years. The poorly drained land tends to need work every two or three years to resolve compaction and slumping.”
Maintaining and updating drainage is a long-term project for the farm. “The weather over the last two years has pushed some of the older systems past the tipping point.”
“We have redrained about 50% of the problem areas in the last eight years, it’s a considerable investment but worth it when you see the end result. More consistent crops with fewer grass-weeds and a wider drilling window. We also regularly mole plough which helps lift the soil in a no-till system.”
The farm operates on a six-year rotation including two first wheats, winter beans, spring oats and canary seed. Oilseed rape is only grown on lighter land, it’s too high risk on heavy soils.
“Financially, the system stacks up with a better margin across the whole rotation. We are not as invested in machinery, agchem and fertiliser, it’s a lower risk system. Previously grass-weed pressure and machinery costs were a constant concern.”
Mr Lord is confident he has black-grass under control but doesn’t take anything for granted. “We are mostly first wheats, so we can drill a little bit earlier, the lower pressure fields go in at the start of October and we ain to finish in mid-October.”
He uses a flufenacet based pre-em programme on farm, with a more robust stack on problem areas. One part of the farm has Italian ryegrass where he opts for cinmethylin and follows up with hand rogueing.
“We hand rogue ryegrass to prevent resistance, particularly to glyphosate. In a no-till system you cannot risk repeat applications to ryegrass because there is no cultivation to control weeds another way.”
“In the past, we were using two or three smaller doses of glyphosate on stale seedbeds. Now we probably use the same amount but in one application to control mixed weed populations ahead of planting.”
Spring cropping is also an important part of herbicide stewardship by breaking up the weed life cycle and reducing the total herbicide use across the farm.
Apply a sufficient rate to kill the target weed
That's at least 720g/ha glyphosate for black-grass and 1080g for brome, ryegrass and couch
Keep to a low boom height
Travel at a maximum speed of 12km/h
Attention to detail is essential for resistance management
Applied correctly, glyphosate as a non-selective herbicide can deliver very high levels of weed control. As such, it has become one of farmers’ most trusted weed management tools. However, experience around the world shows that glyphosate is not invincible, weeds can develop resistance to it. Download our guide for information on reducing those resistance risks.
In January 2025, WRAG announced the first case of glyphosate resistance in the UK in an Italian ryegrass population in Kent. The farm in question has taken steps to prevent the spread of any resistant seed. Other farms should prevent the development of resistance in the field by following glyphosate stewardship guidance. To learn more about this case of resistance, please read our FAQs.
In 2021, the Weed Resistance Action Group (WRAG) published updated guidelines to minimise the risk of glyphosate resistance developing in the UK. This booklet guide builds on their recommendations and Bayer’s expertise with Roundup (glyphosate) products to give farmers and agronomists an effective framework to ensure the long-term efficacy of glyphosate.
The possibility of glyphosate resistance developing in problem weeds such as black-grass and Italian ryegrass is real and needs to be taken seriously. All of the following increase the chance of it happening.
Population dynamics
High weed populations tend to increase the risk of resistance development. Taking action to drive down numbers reduces the risk.
Lack of diversity in control methods
Reliance on few or only one method of control greatly increases the risk of resistance developing. This applies to chemical and cultural control methods, the more diversity across the cropping cycle, the better.
Repeat applications to survivors
A small number of weeds often survive a herbicide application. In all likelihood, this is not due to resistance but because of application or field effects. In any case, take no chances, ensure survivors are controlled with another chemical mode of action or cultural method. Repeat applications of glyphosate to surviving weeds is a major resistance risk.
Low rates
Insufficient application rate for the target weed and poor application timing means too many weeds survive the application. These surviving weeds are a potential resistance risk and an immediate problem for farmers aiming for clean, high-yielding crops.
Poor application technique
Incorrect sprayer set up and operation can result in under or overdosing the product, affecting performance in the field. In the long term, this can contribute to resistance development. Examples of poor application technique include:
Poorly maintained machinery which is not routinely calibrated and serviced
Incorrect selection of nozzles for the job at hand and/or not replaced when worn out
Operating at the wrong boom height and travelling too fast (+12km/hr)
Additionally physical losses from drift, run-off and bounce, and chemical losses due to pH, hard water and light degradation can all reduce the quantity of active reaching the target hence causing below par control.
Incorrect timing
Adverse weather conditions and weed growth stage can both impair glyphosate performance. For example, poor downward translocation will occur during the stem extension phase of growth. The natural flow of sugars from photosynthesis in the leaf is upwards to the rapidly extending stem for use in the developing flower head.
Resistance management framework
Resistance management requires attention to detail, the following framework aims to:
Reduce weed pressure in the crop and improve yield
Prevent excessive seed return
Reduce chances of selection for resistant weeds
Keeping control within the guidelines
Black-grass and Italian ryegrass are high risk weeds for resistance development. They already greatly affect many farmers cropping and weed control strategies. Glyphosate has an important role helping growers manage grass-weed populations, but farmers need to be mindful of glyphosate stewardship and responsible use to help retain effectiveness in the longer-term.
WRAG recommends a maximum of two glyphosate applications after harvest, before drilling the next crop. This applies equally to autumn and spring sown crops. Between applications, use cultivation to eliminate any survivors.
Where cultivation is not possible or not desirable, for example no-till systems, only one application is recommended after harvest and before drilling
Multiple applications of glyphosate before drilling, such as repeat stale seedbeds to control black-grass are not a sustainable way to use glyphosate.
Ensure that every glyphosate application achieves the best possible control.
Use the appropriate dose rate for the target weed; for mixed weed populations, tailor dose rates to the hardest to kill weed.
Target small weeds which are much easier to control than larger well-established weeds
Partner products (and adjuvants) cannot substitute for an effective dose of glyphosate, do no cut rates
Optimise application practices:
Ensure spray application machinery is tested in line with legislation, routinely calibrated, including replacing worn nozzles
Nozzle choice and droplet size suitable for the target, generally bigger weeds require a coarser spray and larger droplet size
Water volume, balance achieving a high concentration of active and ensuring full coverage of the canopy
Appropriate boom height to minimize drift risk, but ensure correct nozzle orientation and spacing to achieve the necessary overlap with adjacent nozzles to deliver a consistent spray pattern across the width of the boom
Forward speed, higher forward speeds increase the risk drift and turbulence leading to uneven spray deposition; 10-12km/h is typically a safe forward speed to ensure efficacy
Aim to apply in conditions which favour best efficacy: warm temperatures (15-25˚C) are optimum; avoid periods of prolonged frost; avoid treating immediately ahead of rain events
Monitoring
It is important to monitor the success of the overall herbicide programme and investigate reasons for poor levels of control as an important component of a successful long-term weed management plan.
Looking for advice on amenity glyphosate use? Visit our FAQ's page for more information.
Read related articles on integrated weed management and discover the best advice on physical, chemical and biological control methods, to protect the yield potential of your crops.
Read related articles on integrated weed management and discover the best advice on physical, chemical and biological control methods, to protect the yield potential of your crops.
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