Chemical gardening: the impact of DDT, neonicotinoids and glyphosate

Val Bourne / 02 September 2019

How pesticides such as insecticides and weed killers old and new can be dangerous to human health and the environment.



It can't have escaped your notice that wildlife is in trouble right across the board. The reasons are complex and they include loss of habitat and climate change. The use of pesticides on farmland and in gardens has also been responsible because these products target the small invertebrates that sustain lots of creatures including birds and many small mammals. Spraying for aphids and flea beetles, for instance, has a knock-on effect on other creatures such as ladybirds and spiders.

There are fewer wildflowers and undisturbed areas because farmers tend to plough right up to the edge. Larger machines mean fewer hedges this also has a knock-on effect on our wildlife because many pollinators rely on native wildflowers because they've built up such a special relationship with them over millennia.

DDT after the ban

Pesticides are not only affecting wildlife, there also taking their toll on human beings. Insecticide DDT (Dichlorodiphenyltrichloroethane) has recently been implicated in causing dementia in research carried out in the United States. Sufferers were found to have four times as much DDT in their bodies.

DDT was banned in Britain in 1986. The catalyst was a decline in birds of prey, because this chemical softened their eggshells and that could have led to extinction.

Larger birds of prey accumulate toxins in their bodies because they’re at the end of the food chain – and we are in the same position. There are many of us who store DDT in fatty tissue, without knowing it, and many will have been born long after the ban as DDT stays in the environment and it’s still here thirty years after its ban.


Neonicotinoids and bees

River mud has been found to store many chemicals and not only DDT. Neonicotinoids have been found as well and these have been shown to affect bees. Many plants on garden centre benches, bearing the logo ‘I’m bee friendly’, have been found to have been sprayed with neonicotinoids so they’re not bee-friendly at all, quite the opposite. Three ‘neonics’ have been banned, Clothianidin, Imidacloprid and Thiamethoxam, and can’t be used on oilseed rape, spring cereals and winter cereals. However they can be used to treat sugar beet, various horticultural crops and as seed treatments for winter cereals. Environment Secretary Michael Gove has promised tougher sanctions.

In parts of China the situation is far worse. Dave Goulson, bumblebee expert and founder of Bumblebee Conservation Trust, observed apple tree blossom being hand pollinated by people with a bucket of pollen and a brush. Wild bees simply don't exist in some areas of China. It goes without saying that there aren't enough people to pollinate our crops. We need our bees and that means radically changing our approach to using chemicals in agriculture and horticulture.

Glyphosate dangers and cancer link

At the moment there's a lot of controversy about glyphosate, which is sold under the tradename Roundup. This weed killer contains a cocktail of different chemicals and Garden Organic say that it's 1,000 times more toxic than pure glyphosate. The product’s manufactured by Monsanto and was first registered in 1974 in America.

Recent litigation in the United States of America has found that this chemical, the most widely used agrochemical in the world, has caused one couple, Alva and Alberta Pilliod, to contract non-Hodgkin's lymphoma. These landscape gardeners, now aged 77 and 75, regularly used glyphosate in their work. A World Health Organisation (WHO) study found that 60% of farmers had glyphosate in the urine and 12% of children also had detectable glyphosate levels.

The jury found that Roundup had been defectively designed and that the company failed to warn of the herbicide's cancer risk and that the company acted negligently. Monsanto have appealed, but there are 13,000 people awaiting the outcome of the result because they've also initiated lawsuits against this chemical. It is the third such courtroom loss for Monsanto. B&Q and Homebase have already said they will stop stocking this chemical and it's thought a ban will eventually follow. Much of the information on the Internet says that glyphosate is still safe and this is almost certainly wrong.

As an organic gardener I wouldn't use any spray including Roundup. However in the past, on gardeners’ question times, I have recommended it for clearing pernicious weeds, because the makers always claimed that it broke down in soil really quickly. However it has been proved that this isn't the case. It's found in the soil and sediments in cooler climates, and that includes the UK, for up to 3 years after use.

Amphibians are thought to be affected by Roundup and common frog numbers have dropped because they come into contact with the chemical when they're on the ground. The common toad is said by the UK charity Froglife to be declining rapidly. Glyphosate is water soluble and has had significant effects on species that underpin the entire aquatic food chain so amphibians are very vulnerable.

Glyphosate is also said to upset the balance of microbial communities in soil, increasing the numbers of some microorganisms and decreasing others. Birdlife is certainly impacted when this chemical is used on weeds and wildflower because many seed-eating birds find themselves short of food. Butterfly food plants are also disappearing. It has caused an upsurge in some crop diseases in no-till agriculture by stimulating the growth of a number of fungal pathogens. It also binds micro-nutrients in the soil causing deficiencies in plants. Glyphosate has also been found to have adverse effects on earthworms, beneficial insects and bees.

It isn’t all gloom and doom! Wildlife can come back with your help and if you’re in doubt read Wilding by Isabella Tree.

Get rid of weeds the organic way

Before you get rid of any weeds, ask yourself whether it's necessary because over tidy gardens are not good for wildlife. A wild, sunny corner with some nettles will help butterflies.

Don’t see weeding as a chore - little and often is the way.

Paths and paving cause particular problems. Try to ensure that gaps between paving slabs are filled with mortar rather than sand.

Diamond hoes are the most effective tools, because they have four sharp points that can be scraped through crevices. Try the De Wit diamond headed hoe, available from Crocus.

There are also effective L-shaped hand tools designed to get between slabs. Rolson and Fiskars both make Stainless Steel Hand Weeder knives.

Gravelled areas can be problematic, but there are weed-burning torches, powered by butane canisters, that scorch away weeds. You can also use boiling water, although this will harm wildlife.

Mulching also helps to suppress weeds because many of them need to be exposed to the light to germinate. You can add soil conditioner and you can also buy green waste, although there is no guarantee that this won't contain chemical residues.

Try not to disturb the soil in spring because you will get a rash of weed seedlings. Should this happen a small hoe will remove them.

More pernicious weeds need to be dug out and worried on a regular basis.

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