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Well, we wouldn't be here, for starters! Neither we, nor anything else on this planet, would be alive. Chemicals are what we are – because the basis of all living things, as well as rocks and soil and sky and sea – is chemistry. As one scientist has put it, "a chemical is an identifiable constituent of every organic compound".
So to talk about spraying – or not spraying – "chemicals" in our garden is a bit of a misnomer.
When practitioners of "organic" gardening talk about not controlling pests and weeds with chemicals they are generally talking about manufactured synthetic chemicals which have been proved harmful to other organisms.
DDT is a good example of this. Once thought of as the saviour of Humankind, at least in terms of pest-free food production, it proved to have such damaging effects on other life forms, such as reproduction in birds, that it was withdrawn from common use. Other manufactured chemicals have proved similarly harmful to humans, birds, mammals, reptiles and fish. Once ingested via the food chain they can play havoc with our health in all sorts of horrible ways. Cancer, genetic disorders, organ destruction and damage to the nervous system are just some of the horrors we associate with chemical toxicity.
Today, in countries with high health standards, chemical products that have been proven harmful to human health are not licensed for use in agriculture, commercial horticulture or the home garden. Those products that ARE readily available to us through hardware stores and garden centres are deemed harmless to humans (unless ingested or applied directory to the skin). However this does not mean that these products cannot harm other life forms in the environment, particularly if used carelessly or to excess.
It's important to know the difference between the chemicals used for control of pests and weeds in gardens. In brief, "natural" chemicals are those that occur naturally in the environment. Synthetic chemicals are those that don't appear naturally in the environment and of these the most environmentally damaging are the organophosphorus pesticides because they kill (rather horribly) by irreversibly inactivating a vital enzyme. By contrast, the carbamate insecticides, derived from the organic compound carbamic acid, reversibly inactivate the same enzyme and are thus less drastic. Old-generation garden insecticides did their deadly work by, put simply, covering the plant (usually the leaves) in an adhesive contact poison that killed pretty well whatever ate it or even landed on it. New-generation systemic insecticides, by comparison, are absorbed by the plant through the leaves or roots and kill only those insects that actually devour the leaves, such as caterpillars and hoppers.
In line with the GardenEzi philosophy of making all aspects of gardening easier, let's look at the most common garden-use chemicals – synthetic and natural - to see what effects they have around the garden.
Confidor – otherwise marketed as Bayer Complete Tree, Shrub and Garden Insect Control. The active chemical is imidacloprid, a systemic chemical. This is a very effective pesticide against a range of otherwise hard-to-kill insects and though it has (so far) proved remarkably benign in the environment, it DOES kill bees, other pollinators, and "beneficial" predators that eat other insects. Thus this product should NEVER be used on (or near, if you are a careless sprayer) plants that are in flower.
Glyphosate – a weak organic acid compounded of glycine and phosphonomethyl, usually marketed under the brand name Round-Up. This product kills weeds, not insects, and is therefore, like most weedicides, much safer to use in the garden. It breaks down fast in the environment but can contaminate water run-off in the short term with sufficient toxicity to kill or adversely affect the health of fish and other aquatic life.
Diazinon – a synthetic organophosphate marketed under names such as Gardentox, Knoxout and Dazzel. Used as a general garden insecticide. It breaks down quickly in the environment – usually within a few hours and no longer than two weeks - and is not considered carcinogenic or a major risk to humans and other mammals (unless directly ingested). Nonetheless it's now banned in the United Sates (as a garden product) and is such a nasty toxin, with such a drastic effect on many insects, that it's hard to believe that it wouldn't have an equally severe effect on birds, mammals and pondlife.
Carbaryl – a carbamic insecticide marketed most commonly as Sevin. It's very toxic to insects ...including bees - but not found dangerous to humans or the general environment (unless you swallow it!). Even so, it has been banned in the United Kingdom and several other countries.
Dimethoate – a synthetic organophosphate that kills insects rather horribly and is also highly toxic to fish and other wildlife if directly exposed. Marketed under names such as Rogor. As it breaks down quickly in the environment it is not considered
Meltadehyde – a molluscicide (slug and snail killer) marketed under names such as Blitzem. This is a very savage stomach poison and though it is combined with a bitter-tasting chemical agent to deter children and pets from eating it, it's still a risk to wildlife – mainly because while they might not eat the pellets they can still ingest the slug or snail. The effects of meltadehyde would appear to be very specific to molluscs, but if the chemical is considered risky for children and pets then wouldn't it be dangerous to other life forms too? I feel this product should only be used in city gardens which are not visited by small wild things, and should be covered so that birds can't reach the pellets. Organic gardeners use natural things such as coffee grounds and sawdust to repel slugs and snails, and this is a safer remedy. Metaldehyde degrades into carbon dioxide and water so has no residual effect in the soil.
Fenthion – sold under brand names such as Lebaycid and Baycid. A seriously horrible nerve poison that kills by contact and through penetration. Effective against a wide range of insects including aphids, thrips, bugs, caterpillars, crickets, moths and spiders – a real super killer because it is fairly toxic to mammals and is also used to poison nuisance birds. Its use in the home garden is restricted to ornamentals (NOT fruit and veg!) but even so, I wouldn't use it in mine!
Pyrethrum – insecticides made from this member of the chrysanthemum family fall somewhere between "natural" and "unnatural" chemicals. The active ingredients - pyrethrins – are highly toxic to most insects through contact or ingested, and have a very fast knockdown effect. Pyrethrum is formulated as a spray, dusting powder or fumigant. For garden use it is often combined with the chemical piperonyl butoxide which maintains the toxicity level and increases effectiveness. A Buddhist wouldn't use pyrethrum in the garden because it kills insects by paralysis – not a very kindly death! What's more, it targets beneficial insects as well as pests. It doesn't harm other wildlife though (except for aquatic life) and is therefore considered a comparatively benign pesticide.
Synthetic pyrethrum – this has long been available and appears to have much the same properties as the natural product, but using it DOES mean putting a synthetic chemical into the natural environment. One such product is Mavrik, the pyrethroid TAU-fluvalinate, which is formulated to kill chewing and sucking insects such as cabbage white butterfly, and also controls mites, aphids, dimpling bug and thrips. Mavrik is said to be low toxic, even to bees, and appears to have little adverse effect on the environment, especially as it is easily broken down by rain, sunlight and bacteria.
Neem oil – marketed under several brand names, usually with the name "neem" included. The active ingredient, azadaractin, affects the hormonal system of chewing and sucking insects and inhibits most processes, including reproduction. The end result is eventual localised population decline in the affected pest, especially insects with a metamorphic cycle such as caterpillars/moths. Neem is said to be systemic to a degree, but the plant's ability to actually absorb it into the system is pretty well limited to the roots; thus applying neem to the soil is likely to be more effective than spraying the leaves. The problem with most neem-based products is that they contain so small a percentage of the chemical that they are not all that effective, especially in cooler climates. What's more, re-application is needed after heavy rain. In my experience a formulation that contains less than 3% neem is not much use. Nowadays there are stronger formulations – up to 90% strength – that are supposed to affect a wider range of insects such as mealybugs – basically by smothering them. The question is, won't such products also harm beneficial insects? Can a "natural" chemical still be termed "organic" if it acts as a broad spectrum remedy that, whatever its methods, disrupts the natural processes of the insects it destroys? I still prefer neem to synthetic organoposphate-type solutions because it doesn't harm other life forms and breaks down very fast in the environment. But it does need to be used with knowledge and caution.
Insecticidal soap – this is made from salts derived from fatty acids, obtained from animal fats and/or plant oils. Some types (the most effective) are made from petroleum oil. The soap works by smothering insects to death and works mainly on soft-bodied types like two-spotted mite, aphids, thrips and mealybugs. It works well if thoroughly applied and is very good for washing away sooty mold and other deposits on plant stems and leaves. It does not inhibit reinfestation, though, and has to be applied every time a new infestation occurs. Certainly one of the more environmentally-friendly garden remedies.
Something else that needs to be considered when dealing with garden chemicals is that the main "killing" ingredient is often blended with a polymer, or adhesive, or wetting agent or some other substance to render the product more usable and efficacious. These add-ons, while subject to the same watchdog scrutiny as the actual toxin, may themselves still be mildly toxic. When it comes to environmental harm from applied chemicals, it's often the accumulation of toxicity rather than individual and specific applications, that are the problem. The more we use, the worse it gets.
What we have to remember above all is that "safety" rating with garden chemicals is mainly concerned with human health. The wider environmental impacts are not always either well-understood, well-researched or well-considered. Also, we are keen to approve chemicals that kill insects dangerous to humans, such as mosquitoes and flies – even though this generally means death to bees, other pollinators, and beneficial insects that prey on the very pest insects that prey on us – and our plants too. In a chemical world there are tough choices to make!
So, is all this a blanket condemnation of all pesticide use in the home garden?
No, it is not. It's a plea to understand the difference between synthetic chemicals and those that occur naturally in the environment. To know which chemicals are harmful and which are comparatively benign, and use only the latter in your garden. It's a plea that you read the label before you buy.
Above all it's a plea to use deterrents rather than killer toxins. To repel pesky insects rather than poison them outright and put that poison into the food chain. This is where the organic remedies come in; herbal products, garlic spray, chilli, pesticidal oils made from natural instead of synthetic chemical substances can all be used for this purpose. True, they are not nearly as fast-acting or effective as synthetic chemical solutions and in severe cases, where precious plants are under threat, gardeners are going to want something that really works.
When that time comes, make sure the products you use are as target-specific and environmentally benign as possible. Avoid products that kill a whole range of insects because a healthy garden depends on a vital interaction between many different insects, plants, birds and other organisms.
Remember Joni Mitchell's appeal to farmers in her song Big Yellow Taxi?Give me spots on my apples and give me the birds and the bees? We can't do without chemicals because Chemicals R Us – but we can certainly do without those that damage the delicate web of life.
You'll find plenty more good gardening information at www.gardenezi.com.
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