THE HISTORY OF WEED CONTROL: HOW DID WE GET HERE?

What is a ‘Weed’?

The simplest definition is ‘A plant growing in the wrong place’.

One man’s problem plant, may well be another’s favourite flower. There is actually no such thing as a ‘weed’, it is simply down to one’s own opinion.

How long have we all been trying to kill ‘weeds’? Well… whether it’s a recurring dandelion on your drive or a pesky creeping buttercup that’s ruining your lawn – weeds have been with us for an awfully long time.

My first experience of weed issues were watching my dad dig horsetail out of his drive and I remember being fascinated by the length of the root system and the depth at which it grew. I also remember my dad’s frustration that no matter what he did – it still kept growing back.

Fast forward to today and I have the same horsetail issue on my drive at home – not helped by my neighbour refusing to allow any herbicide treatment within his boundary – so no matter what I do within my garden it continues to grow back from his side.

In the scheme of things, garden management is a minor consideration when compared to the control of plants which disrupt food production. Anything that reduces yield from farms will attract commercial interest in finding ways to maximise crop and minimise wastage.

Before we had herbicides, weeds were managed through a combination approach using physical, cultural and in some examples chemical control. Hand weeding using manual tools like hoes and hand pulling.

Other practices included crop rotation and adjusting the crop planting times. Huge levels of manual labour were required to keep on top of weed growth and costs were high. Grazing animals were often cited as an alternative weed management system with horses, goats and cattle being encouraged to eat the surface growth of heavy weed infestations.

 

History

In the early 20th centuries, inorganic chemicals like sulphuric acid, kerosene, arsenic and copper salts were used which were often ineffective, toxic or flammable.

Commercial chemical weed control is largely a 20th century phenomenon. Prior to this period, there was no serious consideration that poisons could be used selectively within crops as they were too closely related biologically to the crop plants that were to be protected.

Anything that killed the unwanted invaders would also kill the crop plants.

Salt (Sodium chloride) was first tested for non-selective control of common hawkweed in Vermont in 1896 and for Field bindweed control in Kansas in 1915. Carloads were used along highways, rail lines and rights of way at rates of about 20 tons per acre. Little thought was given to the environmental impact of these strategies or the ongoing damage to topsoil and the impact of run off into watercourses and the longer term damage caused.

In about 1900, copper sulphate was used for control of wild mustard amongst oats. Soon after came chemicals such as calcium cyanamide, sodium chlorite and sulphuric acid.

Sulphuric acid was used in in France and the USA in the early 1900’s for control of annual broadleaf weeds in cereals.

The arsenicals came into limited commercial use as soil sterilants. Sodium arsenite was used extensively by the Army Corps of engineers for control of water hyacinth in Louisiana from 1902 to 1937 and used widely as an aquatic herbicide in lakes and ponds.

Sodium chlorate was first used for nonselective weed control about 1926.

Synthetic organic selective herbicides first appeared in France in 1932 with the patenting of dinitro-o-cresol (DNOC) for selective control of annual weeds in cereals in cereals. Dinitro-cresols and dinitro-phenols soon appeared, but these compounds had variable effectiveness and could kill animals as well as plants.

With each of these milestones there was renewed interest in chemical weed control and more research in the field.

The phenoxy herbicides ushered in a chemical weed control revolution in the mid 1940’s. This was soon followed by the triazine herbicides and others in the 1950’s. With the advent of more chemicals in agriculture weed science became a discipline and a professional career choice.

In 1957 there were approximately 100 weed scientists in North America but over the next few decades this number grew to several thousand.

Farmers were looking to get uniform crop fields without weeds – typically their strategies involved frequent cultivation followed by hand hoeing or rogueing of remaining weeds. However, the benefits of the triazine herbicides were obvious – reduced labour costs, lower fuel costs and reduced need for cultivation – plus easier harvesting.

Soil quality was also improved due to less soil erosion.

Suddenly with a single chemical application a farmer could avoid many weeds during the entire growing and harvesting season.

 

Japanese Knotweed Solutions Ltd

In early 2000 when Japanese Knotweed Solutions Ltd (JKSL) was set up, the main chemical recommended was Picloram, a residual herbicide. The benefits of its residual nature were that any re-growth after initial treatment would be picked up by the chemical still active within the soil profile. JKSL were asked by the supplier of the chemical to conduct field trials with Picloram and to report back on efficacy.

Picloram was sold as ‘22K’ and used to provide an active chemical layer beneath building footprints where Japanese knotweed had been excavated and removed. JKSL used the chemical to provide a layer beneath car parks and building footprints through which Knotweed would not grow, this providing a ‘belt and braces’ approach to prevention of re-growth.

Residual herbicides could not be used within set distance from watercourses or open drains.

Residual herbicides were removed from the approved list in June 2015 due to concerns relating to movement within the ground and the potential of contamination of water courses and is no longer available as a treatment option in the UK.

At the time, JKSL were concerned that without use of residual herbicides the fight against Japanese knotweed would be lost.

Other chemicals were recommended, which whilst not residual within the soil did prove effective – though the number of visits and re-sprays would often take several years to give a visible benefit.

Glyphosate sold as ‘Icade’ became the ‘go to’ chemical with active ingredients of aminopyralid and triclopyr for use with woody weeds and invasive species.

Glyphosate Gold is an example of a non-selective weed killer – once this professional grade product is absorbed into the root system it will rapidly kill weeds and keep them away.

Roundup ProVantage is the strongest amenity weed killer currently on the market – it is the continuation of Roundup ProActive – however, Roundup ProVantage contains 480grams of Glyphosate per litre rather than 360grams.

SBK has the active ingredient of Triclopyr is an excellent alternative to glyphosate but does not have a long term adverse effect on soil – you can safely replant after only six weeks.

Adjuvants and additional water softeners have also been introduced more recently to aid absorption of the chemical into the plant.

Future

Continued global concerns over the use of glyphosate may well impact on the use of these types of chemicals in invasive species management and control.

Current legislation suggest that the immediate future of glyphosate in the UK market is still safe but there is a growing feeling that potential for more information coming forward in relation to side effects and health issues may well impact on future approvals.

If glyphosate is withdrawn from use, how will we manage Japanese knotweed eradication?

Excavation and removal to licensed landfill is a current method often used by JKSL when construction margins permit the type of costs involved – but to a typical residential home owner, the expense is very prohibitive.

In a world where higher yields per acre are needed to feed our increased population – the removal of vital chemical strategies that reduce costs and increase productivity would be a disaster for farmers and the nations already suffering from starvation.

Whilst there is much to be said for phasing out chemicals that potentially damage the environment – alternative weed management strategies are needed to replace those being removed.

 

Mike Clough

CEO