Dr Anton Rosenfeld and Emma O’Neill take a deep dive into pesticides, looking at their uses and impact – and what alternatives you can use to boot them out of your garden

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Pesticides are chemicals developed to eliminate forms of life in growing areas that we consider to be a nuisance. These could be weeds that compete with our plants, insect ‘pests’ that eat our crops or fungal diseases that make our plants sick. Pesticides can either be artificially synthesised or derived completely from natural sources.

As an organisation, we believe there’s no place or need for pesticides in a garden. They can be harmful to health and damage soil and wildlife, as well as leaching into water courses. We would like to see their removal from all supermarket and garden centre shelves.

Different types of pesticide

But what kinds of pesticide are you most likely to see, and why are they so bad for you and your garden?

‘Pesticide’ is an umbrella term. Types include herbicides (designed to kill plants), insecticides (which kill insects), fungicides (fungi), rodenticides (rodents) and molluscicides (molluscs).

The term also includes synthetic plant growth regulators (which modify plant development so they can grow out of season), defoliants (that accelerate leaf fall) and desiccants (which dry leaves out so they can be harvested).

What are herbicides

Herbicides or weedkillers are chemicals that kill off weeds and are used in agriculture, gardening and in public places such as parks and paved areas. The most commonly used herbicide worldwide is glyphosate. It was launched by Monsanto in 1974 as Roundup, a broad-spectrum weedkiller.

Glyphosate blocks the shikimate pathway (the metabolic route) used by plants, fungi and bacteria to make proteins. Because this pathway is absent in animals, glyphosate was initially deemed to be completely safe and agrochemical companies even touted that it was safer than table salt.

Fast forward 50 years and the safety claims don’t look so rosy. There’s a good number of studies that indicate that glyphosate can negatively impact soil life including reduced mycorrhizal and earthworm activity, both essential for a healthy soil. (1) More recently, glyphosate has been widely used to desiccate cereals before harvesting, and this has led to residues commonly being detected in cereal products. (2) In fact, UK government testing results in 2021 showed 50% of bread samples contained pesticide residues including glyphosate. (3) Although many argue that these residues are below the acceptable daily intake levels, a body of recent work has shown that these limits have been set far too high, and alarmingly, doses well below those considered safe by EU pesticide law caused multiple types of cancer. (4,5)

Some formulations of Roundup are now labelled ‘glyphosate free’. These tend to contain pelargonic acid, a plant-derived acid that will burn foliage but have much more limited persistence in the soil.

What are insecticides

Insecticides have been used for thousands of years, with sulphur being used as a fumigant in Greek and Roman times. It was in the 1930s that chemically synthesised insecticides really took off, with DDT being the most notorious. It prevented many deaths from malaria, but also became a highly persistent pollutant, and is still found contaminating foods today even in areas where its use was banned more than 40 years ago.

More recently, there has been the scourge of widely used neonicotinoid pesticides. These are incredibly potent, as a single seed coating allows it to be taken up into all tissues in the plant with the toxin remaining active all throughout the growing season. Not surprisingly, neonicotinoids have been found to cause significant damage to pollinators and many other non-target organisms. Only about 5% of the ingredient is taken up into the plant and the rest disperses into the wider environment. (6) Neonicotinoids were also widely found in the pollen of nearby wildflowers gathered by bees. (7)

There are also many naturally derived insecticides. Natural soap or oil-based formulations are the most popular and commonly sold to gardeners. These tend to have a lower environmental impact as they just target the pores of soft bodied, sap-feeding insects (e.g. aphids) and break down quickly after use.

Some garden products contain pyrethrum, which is derived from chrysanthemums. Although a natural product, these are still broad-spectrum insecticides, targeting a variety of insects rather than one individual species, and will kill pollinators if sprayed in their direction, so should not be thought of as a ‘safe’ organic replacement for synthetic pesticides.

What are fungicides

As with insecticides, farmers have been using simple fungicides, such as sulphur, for thousands of years. Perhaps one of the most notable inventions is the Bordeaux Mixture, which was developed in 19th century France and sprayed on to grapes to prevent mildew. Chemical fungicides really took off in the 1940s, when a wide arsenal of products were developed.

As with other chemicals, fungicides come with a range of risks that were reviewed in a UK government report in 2023. The key risks include adversely affecting soil, freshwater environments and entering watercourses. There were health impacts to the user and the consumer leading to increased risk of chronic illnesses, including cancer, heart respiratory and neurological diseases and the development of fungicide resistance through continued use. (8)

One of the most frightening issues is the overuse of fungicides in agriculture, which has led to human fungal pathogens developing resistance to common medical treatments. For example, the standard treatments for Aspergillus fumigatus, a fungus that causes respiratory disorders, have become increasingly ineffective in recent years. (9)

Although pesticides are still widely used, thankfully a tightening of regulations has reduced the number that are available for growers. It’s also becoming a more costly process to develop new ones when licences expire.

Resistance is also a big problem with herbicides, insecticides and fungicides. There are examples of weeds, insects and fungal diseases that no longer respond to the common chemicals deployed.

Alternatives – such as tolerant varieties, use of biocontrols and biostimulants and cultural measures such as mechanical weeding – need to be more widely employed. However, with 60% of global seeds sold controlled by four agrochemical companies, big agribusiness are unlikely to be in a hurry to get rid of systems wedded to pesticides.

Alternatives to pesticides

Head gardener Emma O’Neill outlines ways you can tackle pests and diseases in your garden without reaching for the toxic chemicals

We understand the thought of your crops being destroyed after all your hard work is demotivating and frustrating. In our organic demonstration garden, at Ryton, we try to mitigate these problems with prevention first.

1.    Your growing space needs to be awash with activity from beneficial insects, mammals, birds and amphibians – to act as natural predators that will assist in combating any ‘pests’. So put the effort into making your area as diverse as possible. To attract this army of helpers, use a wide range of plants both edible and ornamental, which will also help in suppressing weeds through their growing habit.
2.    Soil is a key component to prevention; healthy soil leads to healthy plants that can withstand most problems thrown at them. Make full use of cover crops such as green manures and mulches (i.e. your own compost) to improve your soil structure and add nutrient content while protecting the soil from leaching and degradation.
3.    Practise good hygiene to stop the spread of diseases: wash your tools after use to prevent cross contamination and always sweep up after yourself.
4.    ‘Right plant, right place’ was one of the first lessons I was taught at horticulture college. The right plant for your environment means that it will thrive, and healthy strong plants are more robust and less susceptible to problems. Don’t try to grow acid lovers in alkaline soil or sun lovers in shade, they will be weak and struggle to establish making them easy pickings for ‘pests’.
5.    At Garden Organic we work hard to get the balance right in our demonstration garden and favour good old-fashioned hand weeding or light digging to tackle our weeds. We also sow plenty of cover crops to aid our soil and fill bare ground with diverse plants.
6.    We regularly remove ‘pests’ by hand – but first we hold our nerve and watch closely for any natural predators to arrive. If that fails, where necessary we will use bio controls such as nematodes.

References 🔗

1. Soil Association. The Impact of Glyphosate on Soil Health. 8 (2016).
2. Xu, J., Smith, S., Smith, G., Wang, W. & Li, Y. Glyphosate Contamination in Grains and Foods: An Overview. Food Control 106, 106710 (2019).
3. Claydon, S. The Dirty Dozen. Pesticide Action Network UK (2025).
4. Weisenburger, D. D. An Update of Evidence that the Herbicide Glyphosate (Roundup) is a Cause of Non-Hodgkin Lymphoma. Clin. Lymphoma Myeloma Leuk. https://doi.org/10.1016/j.clml.2025.11.005 (2025) doi:10.1016/j.clml.2025.11.005.
5. New scientific publication confirms glyphosate causes cancer at EU “safe” exposure levels – evidence ignored in EU reapproval. PAN Europe (2025).
6. Wood, T. J. & Goulson, D. The environmental risks of neonicotinoid pesticides: a review of the evidence post 2013. Environ. Sci. Pollut. Res. 24, 17285–17325 (2017).
7. David, A. et al. Widespread contamination of wildflower and bee-collected pollen with complex mixtures of neonicotinoids and fungicides commonly applied to crops. Environ. Int. 88, 169–178 (2016).
8. Brown, T. Agricultural Fungicides: Impact on Long-Term Food and Biological Security. https://lordslibrary.parliament.uk/agricultural-fungicides-impact-on-long-term-food-and-biological-security/ (2023).
9. Lockhart, S. R., Chowdhary, A. & Gold, J. A. W. The rapid emergence of antifungal resistant human-pathogenic fungi. Nat. Rev. Microbiol. 21, 818–832 (2023).