Tractor spraying herbicide onto a field

The herbicide glyphosate was first registered in 1974 under the original trade name RoundUp (Monsanto) and has since become one of the most commonly used herbicides globally.

It is a non-selective, post-emergent herbicide with a wide range of uses including arable, forestry, and horticulture.

Below is an overview of the topic of glyphosate. Any relevant projects, pages and initiatives will be linked to this page to provide more in-depth information and research.

 

How does glyphosate work?

  • Glyphosate is classified under HRAC Group 9: Inhibition of EPSP synthase.
  • EPSP synthase is an enzyme involved in the synthesis of important amino acids (tryptophan, tyrosine and phenylalanine) within plants. By blocking the action of this enzyme, glyphosate herbicides prevent weeds from producing key proteins needed for survival. 
  • Glyphosate is applied to the leaves where it is absorbed. Once inside the plant it enters the plants transport system and is circulated systemically.
  • Symptoms of glyphosate injury are quite varied and can include chlorosis, leaf distortion, stunting of growth and ultimately death of the affected plant. 

Glyphosate in the UK

  • Glyphosate remains approved for use until at least 2025 in the UK.
  • Due to the non-selectivity of glyphosate, products containing it are often used on weeds prior to sowing or planting of crops, or target-applied to avoid crop damage.
  • Product labels for all UK CRD approved herbicides containing glyphosate will explain  usage restrictions including timings of application, appropriate doses and safety.

Resistance

  • Currently in the UK there are no characterised resistant populations to glyphosate. However there have been signs that decreased sensitivity is developing in several weed populations (particularly a problem in black-grass).
  • Furthermore confirmed glyphosate resistance has been documented in other countries.
  • With such high dependence on this herbicide it is vital that the UK resistance risk is minimised (e.g by incorporating suitable cultural controls and rotating herbicide modes of action) and monitored closely (e.g regular resistance testing).

Genetic modification 

  • In many countries (not the UK), commercially grown crops have been genetically modified (GM) to be herbicide tolerant to glyphosate. These herbicide tolerant crops were first introduced in 1996 with the Roundup Ready soybean.
  • These Roundup ready soybeans contained a mutated version of the EPSP synthase enzyme, taken from the bacteria Agrobacterium sp. This altered form of the enzyme rendered the soybeans glyphosate insensitive.
  • Since then, several molecular mechanisms of conferring resistance have been used and a variety of GM glyphosate tolerant crops commercialised globally.
  • By planting glyphosate tolerant crops, it means that glyphosate can be sprayed onto crop fields as a post-emergent herbicide, killing all weeds present, but leaving the cultivated crop intact and healthy. 
  • However, intensive use of herbicide tolerant crops can put high pressure on weeds to develop resistance, which has now been confirmed in several countries

 

You can visit the AHDB website and use Weed Resistance Action Group (WRAG) resources to find out more information about glyphosate and get resistance updates for the UK.

Related Organisations

Content below is from across the PEP community and is not necessarily endorsed by Stewards or by PEP

Connected Content

NiCCs (Nitrogen release from Cover Crops)

Project objectives To quantify the impact of contrasting cover crop mixes and destruction techniques on over winter nitrate leaching, soil nitrogen supply (and hence crop nitrogen fertiliser requirements) and performance of the following cash crop. In particular to determine the: effect of cover crop species mix on the quantity and timing of nitrogen returned to the soil effect of cover crop destruction method e.g. glyphosate & min till/direct drill vs mechanical destruction & min till/direct drill To determine the timing of nitrogen release from cover crops and potential legacy (year 2) effects on nitrate leaching and crop performance

Herbicide Resistance

Herbicide resistance is the inherited ability of a weed to survive a rate of herbicide which would be lethal to a member of the normal population. It can develop over time based on repeated selection pressure imposed on the weed. This selection pressure changes the population from susceptible to resistant. Herbicide resistance is becoming an increasing problem in UK agriculture, in both grass weeds and broad-leaf weeds. See also the general topic on herbicides.

Black-grass

Black-grass (Alopecurus myosuroides) is a major weed in winter sown cereals.

Grass Weeds

Grass weeds are a major challenge in UK agriculture and are often highly competitive in arable crops. Some of the most common grass weeds in the UK include: Black-grass (Alopecurus myosuroides), Italian rye-grass (Lolium multiflorum), Brome (Bromus sp.), wild-oats (Avena sp.), Couch grass (Elytrigia repens), annual meadow grass (Poa annua) and Rat's-tail Fescue (Vulpia myuros). You can find specific topic pages for black-grass and brome. See also related topics of: broad-leaved weeds, herbicides, herbicide resistance and integrated weed management

Broad-Leaved Weeds

Broad-leaved weeds are a varied group of weeds that can grow and cause significant problems in arable fields in the UK. Some of the most common broad-leaved weeds in the UK include: Common Chickweed (Stellaria media) , Scentless Mayweed (Tripleurospermum inodorum), Common poppy (Papaver rhoeas), Charlock (Sinapis arvensis L.), Fat-hen (Chenopodium album L.), Common groundsel (Senecio vulgaris), Docks (Rumex spp) and Creeping thistle (Cirsium arvense). See also related topics of: grass-weeds, herbicides, herbicide resistance and integrated weed management.

Assessing pesticide risks to non-target terrestrial plants

A 1998 study commissioned by the Pesticides Safety Directorate to assess the non-target impacts of pesticides on non-target terrestrial plants (NTTP's).  'To conserve and enhance biological diversity within the UK' was a stated aim of of the UK Biodiversity Action Plan (1994). Over 25 years later this is still a vital issue and the UK has stated its commitment to secure a post-2020 Biodiversity Framework as well as developing a 10 point plan for financing biodiversity (UK Government, 2022). However, a threat to plant biodiversity is non-target effects of pesticides - this is when pesticide materials reach areas beyond the target application area and affect the species there. Effects of pesticides on non-target plants can range from lethal (death of the plant) all the way to enhanced growth of these plants. Such varied effects depend on a range of things including the type of pesticide used, the concentration of its active ingredient and the sensitivity and spatial range of affected plants. Importantly, plants are part of complex food and pollination webs and so pesticide effects on plants can have cascading effects on the fauna that rely on them, and vice versa.

Integrated Weed Management (IWM)

IWM involves using numerous weed control methods to try and manage a weed problem sustainably. Whilst herbicides can still be used as part of an IWM approach, a major aim is to reduce reliance on them by also incorporating methods including, cultural, mechanical, biological, thermal and genetic control. A combination of such approaches can allow for optimal control of a specific weed problem. Related topics on FarmPEP include herbicides and herbicide resistance. You can also view the topic pages on grass weeds and broad-leaved weeds which provide examples of suitable control methods.

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