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.
Environmentally Friendly
This metabolic pathway is present only in green plants. Higher forms of life like mammals, birds, fish and insects are dependent on plant sources to obtain these three amino-acids in their food and neither absorb nor metabolise glyphosate. This is the reason Roundup has such environmentally friendly characteristics.
No other class of commercial herbicide is known to target this site (HRAC group G).
Glyphosate Formulations
All glyphosate products are not same. While they all contain the active ingredient, glyphosate, the formulation type in which the glyphosate is carried plays a major role in performance.
Our formulation chemists have worked continually since the launch of Roundup to bring out new formualtions with improved weed control, leass restrictive conditions of use and better safety profiles under COSHH.
Modern formulations of Roundup are highly active and provide the highest levels of uptake and translocation leading to improved speed, rain fastness and efficacy.
Find out more:
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.
Use the links below to navigate to the appropriate section.
Best Practice Information:
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.
The Importance of the Label
The COP is very specific about the need to follow the label as a whole and comply with maximum dose rates, maximum number of treatments etc. Labels now carry this statement:
‘READ THE LABEL BEFORE USE. USING THIS PRODUCT IN A MANNER THAT IS INCONSISTENT WITH THE LABEL MAY BE AN OFFENCE. FOLLOW THE CODE OF PRACTICE FOR USING PLANT PROTECTION PRODUCTS.’
Use of a PPP against the label or the approval automatically results in failure to meet the Statutory Management Requirements under EU rules for farm payments.
Fields and Conditions of Use
All approved pesticides have fields of use listed on the label. The conditions of use must be followed in order to remain within the law and are listed prominently under the product name e.g.
‘FOR USE AS AN INDUSTRIAL/HORTICULTURAL/FORESTRY/ AQUATIC/ AGRICULTURAL HERBICIDE.’
Products which are approved for agriculture and horticulture should not be used in Industrial and Amenity situations unless they are also listed.
The details are listed below the main heading under CROPS/SITUATIONS. It is not always obvious what these crops/situations are so it is vital to make sure you understand before you use a PPP for a situation which is not included on the label. These are all defined by CRD in the Crop hierarchy (Last revised in 2006) which can be downloaded from the CRD website
The information is also in the Code of Practice for using Plant Protection Products on p16,17 table 1.
Example of Fields and Conditions of Use: Roundup Energy label
IMPORTANT INFORMATION
FOR USE ONLY AS AN AGRICULTURAL/HORTICULTURAL HERBICIDE
Crops/situations:
Wheat, (including Durum wheat), barley, oats, combining peas, vining peas, field beans;
Oilseed rape, mustard, linseed;
Sugar beet, swedes, turnips, bulb onions, leeks;
All edible crops (stubble), all non-edible crops (stubble);
All edible and non-edible crops (destruction, before sowing/planting);
Grassland;
Apples, pears; plums, cherries, damsons;
Green cover on land not being used for crop production;
CRD Crop Hierarchy Definitions
Most specific crops listed are self explanatory. However there is sometimes confusion over plant-free areas.
Natural surfaces not intended to bear vegetation. Areas of soil or natural outcroppings of rock that are not intended to bear vegetation, including areas such as sterile strips around fields. May include areas to which the public have access. It does not include the land between rows of crops.
'Green cover on land not being used for crop production' comes under the agricultural/horticultural heading in the crop hierarchy and does not include industrial or amenity situations.
Areas of land with a vegetation cover that have been removed (temporarily or otherwise) from production. For example some types of set aside. Includes fields or non-crop field margins covered by natural regeneration or by a planted green cover crop that will not be harvested.
Does NOT include use in industrial crops or inter-row use within a crop (edible or non-edible).
Other Plant-free areas with industrial and amenity approval are Permeable surfaces over lying soil or hard surfaces.
Permeable surfaces overlying soil: Any man made permeable surface (excluding railway ballast), such as gravel, that overlies soil and is not intended to bear vegetation.
Hard surfaces: Any man made impermeable surface, such as concrete or asphalt and including railway ballast, that is not intended to bear vegetation.
If the situation you intend to use a PPP for is not listed on the product label, then you cannot follow label instructions and comply with the law. You may need to choose a different product which does carry the intended use.
Crop Specific Information
Detailed information is given in a further table on Maximum use rates, number of treatments & other specific restrictions.
Each line in the table represents a new situation and where more than one situation occurs for the same crop it can be sprayed once for each situation. For example in winter wheat you can apply up to 1.2l/ha of Roundup Energy post planting, but before emergence, then up to 3.2l/ha before harvest and up to 5l/ha in the autumn on the stubble.
The Maximum individual dose rate is simply the highest dose you can apply at any one time. The maximum individual dose rate will vary according to the particular use e.g you can apply Roundup Energy at up to 4.8 l/ha on grassland, 3.2l/ha pre-harvest of wheat or 1.2l/ha post planting, pre-emergence of listed crops.
A maximum number of treatments may be specified under the ‘Maximum number of treatments per year’ column for some products. We use a Maximum total dose wherever possible which allows flexibility to split into any number of treatments.
Water volumes in which the product can be applied may also be restricted. Instructions will be given on the label eg Apply in 80-250l/ha of water. In some cases this can be reduced, but the rules are complicated and often do not apply to knapsack use. (See para 4.6.4 COP).
Always read the label carefully and comply with all the label instructions.
Failure to follow label restrictions could result in prosecution.
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. Our guide provides information on reducing those resistance risks.
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.
Fortunately, there are no known cases of glyphosate resistance in the UK but weed biologists agree that the risk is there. Once weeds become resistant, there is no cure, so taking steps to reduce the risk is essential for farmers to retain this versatile and highly effective herbicide.
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.
