Weed management: Alternatives to the use of glyphosate
While the use of synthetic pesticides in agriculture has helped to increase food production, this has occurred at great cost to the environment, natural resources, and human health. The 2017 United Nations (UN) report of the Special Rapporteur on the Right to Food highlights the adverse impact of pesticide use on human rights, human health (workers, their families, bystanders, residents, and consumers), and the environment. The report also reveals that intensive agriculture based on pesticide use has not contributed to reducing world hunger.
Herbicides are used in agriculture and horticulture to combat weeds that, above certain thresholds, compete with crops and pasture for nutrients, water, and sunlight resulting in reduced crop and livestock yield and quality, which in turn reduces profitability. The next most widespread use is for no-till and reduced tillage systems where herbicides, principally those based on glyphosate, are used to kill all vegetation, both post-harvest and also before crop and pasture establishment. A third use is to ripen and desiccate grain and seed crops before harvest. Non-agricultural uses include the management of invasive plant species, assisting the management of public areas, for aesthetics or reducing hazards (e.g., sidewalks, pavements, and railways), or for weed control in private gardens.
There is a widespread belief that herbicides are safe for human health and have little impact on the environment. Based on this belief, mainstream agricultural systems are now almost completely dependent on the use of pesticides, particularly herbicides. Many farmers have abandoned several equally effective, non-chemical weed management methods. As a result, tonnes of herbicides, particularly glyphosate products, are applied every day to fields and their surroundings, which can put human health at risk and negatively impacts biological processes and ecosystem functioning. Herbicide use with a zero tolerance approach to weeds is a major driver of farmland biodiversity decline; this includes loss of beneficial species which could otherwise combat pests. Farmers and growers have become dependent on pesticides and herbicides while many non-chemical alternatives have been lost from the collective memory, so producers end up trapped on a pesticide treadmill.
Herbicides can have a wide range of non-target impacts including direct toxic effects on nontarget species, including soil organisms, invertebrates, and vertebrates, as well as ecosystemlevel effects. But there are also important effects resulting from the intended aim of reducing weeds, which are vitally important food and ecological resources for the other species that inhabit farmland, such as insects and birds. Therefore, there are direct and indirect effects of herbicide use on farm ecosystems that result in the large declines observed in what were once widespread and vitally important farmland species of public concern, including wildflowers, insects, and birds.
Not only do the use of herbicides and pesticides have many negative impacts, but they are also increasingly failing to work due to evolved resistance, i.e., weeds evolve mechanisms that make them resistant to regularly-used herbicides, such that the herbicides no longer kill the weeds. In December 2022, there were 515 “unique resistance cases”, i.e., weed species populations resistant to one herbicide (in 267 species), a large increase from less than ten cases in 19704. Of those, over 100 species are resistant to two herbicide modes of action, and more than 50 species are resistant to three modes of action. Weeds have evolved resistance to 21 of the 31 known herbicide modes of action and 165 different herbicides. As a result, the number of glyphosate-resistant weed species now stands at 56.
Several new European Union (EU) policies demand an urgent reduction of pesticide use in Europe. Glyphosate is by far the most widely used active ingredient of herbicides in Europe. In the EU Green Deal announced in June 2022, “the European Commission adopted a proposal to restore damaged ecosystems and restore Europe’s nature from agricultural land and seas to forests and urban environments, by 2050. As a part of this, the Commission proposes to reduce the use and risk of chemical pesticides, as well as the use of the more hazardous pesticides, by 50% by 2030.” The EU Biodiversity and Farm To Fork strategies6 had earlier specified the two pesticide reduction targets in May 2020. However, at the current rate of use of herbicides, the EU pesticide reduction targets cannot be fulfilled. That is why we need alternatives to the current use of herbicides and particularly the most used, glyphosate.
European citizens are also demanding a radical reduction of pesticide use. In 2022, the European Citizens’ Initiative (ECI) Save Bees and Farmers passed the milestone of 1 million valid signatures. The ECI calls for phasing out the use of synthetic pesticides: by 2030, says the call, the use of synthetic pesticides should be gradually reduced by 80% in EU agriculture; and by 2035, agriculture in the entire Union should be working without synthetic pesticides. Earlier, in 2017, another successful ECI called to ban glyphosate, reform the EU pesticide approval process, and set mandatory targets to reduce pesticide use in the EU; it was officially handed into the European Commission with a total of 1,320,517 signatures collected from all across the EU.
This report outlines the wide range of non-chemical alternatives to herbicides that are already available and used by organic farmers and those practising integrated weed management (IWM). It highlights the critical need for mainstream farmers and growers to make much wider use of these tools, and the need to expand and improve current non-chemical tools, while also developing novel approaches. Using glyphosate-based herbicides as a reference, the current analysis presents a wide variety of weed management approaches that achieve highly effective weed control without the use of herbicides.
By integrating physical, mechanical, biological, and ecological agricultural practices with the broad knowledge acquired on the biological and ecological characteristics of crop plants and weeds, farmers can successfully manage weeds without herbicides, while maintaining yields, avoiding building resistance in weed species, protecting soil health and biodiversity, and minimising erosion.
This report also covers topics such as the use of glyphosate in the EU and globally, general pesticide sales in the EU, and the impacts of glyphosate on soil and environment. Finally, it presents a list of suggestions for the transition towards glyphosate-free and pesticidefree weed management practices. The report draws upon several biological and agronomic principles, such as the “many small hammers” approach to weed management and the IWM hierarchy. In terms of soil, it explains the “living roots all year round” approach and most importantly for IWM, it redefines the concept of a weed by introducing the category of Aliae Plantae (other plants) which are not harmful to the crop but are rather benign to it or even beneficial to the agro-ecosystem. Widespread understanding this could be a game-changer, as farmers would no longer spend time, effort and money in eradicating aliae plantae for no benefit.
Finally, the IWM regime for dealing with docks (Rumex spp.) in pasture has been developed in to a new annex, and the 8 main uses of glyphosate and chemical and non-chemical alternatives to them have been summarised in a table, also in annex.