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The effects of using pesticides

Bindweed is romping through the border, smothering your annuals; slugs have just polished off the line of lettuce seedlings; aphids have attacked your roses; and your expensive viburnum is showing signs of dieback. It's tempting to reach for a spray can or a tin of pellets to swiftly deal with the problem but these pesticides contain chemicals which are powerful enough to kill their target organisms and other non-target ones too and if not properly handled can injure or even poison humans too.

Members of the Crop Protection Association point out on their Garden Care website that the UK and Europe have some of the strictest pesticide regulations in the world and that when used correctly, according to the label, these garden chemical products are safe and may be the only way of saving a plant that is under attack.

Dr Roslyn McKendry of Pesticides Action Network UK, an independent organisation that works to eliminate the dangers of toxic pesticides, says that we now have a smaller number of chemicals available to amateur gardeners than ever before. But, she continues, 'despite the fact that numerous tests are now carried out before products are passed for amateur use, no testing can accurately predict the long-term impact of those chemicals. For example, an increasing number of research papers are linking the development of Parkinson's disease with exposure to Paraquat which was until recently used in some weedkillers in the UK. Other chemicals thought to be ok two or three decades ago are now showing problems too.' She cites atrazine which was found, in low doses, to feminize male frogs and had also been used in various weedkiller preparations. It was withdrawn from the European market when it was found to be extensively contaminating groundwater.

There are several other reasons for not using chemicals in the garden. Many are not target specific and so will kill beneficial insects as well as the pests. Environmental organisations have expressed concern over the effects of neonicotinoid pesticides, used as a coating for agricultural seeds and in pot plants, on the health and life cycle of bees. Regular use of pesticides can also lead to resistance, and so is counter productive. And using chemicals on crops introduces the possibility of residues still being present when the food is eaten.

Advocates of organic gardening are concerned by the recent apparent increase in sales of garden chemicals, due in part to the increasing popularity of 'growing your own'. Horticulture Week reported this trend in June 2009, confirmed by analyst GfK Retail & Technology, with demands encouraged by the weed and slug-inducing wet weather in 2008, the appearance of aphids during the drier spells of 2009 and the novice gardeners' desires for quick and high performing results.

Sally Smith, formerly of Garden Organic, says 'many gardeners desire a perfect lawn and use chemical fertilisers and weed killing products to achieve this. But bowling-green perfection is not necessary for the average lawn, a good quality turf can be achieved using natural feeds applied at the right time and adopting a sensible mowing regime that doesn’t shave the grass too short. Weeds can be removed by hand and attention paid to providing good growing conditions for the grass, good drainage and plenty of sunshine. Lawn grass will simply not grow well under trees and heavy shade.'

Slugs top the list of problem pests for gardeners who ask the RHS for help and advice. But, says Chief Advisor, Guy Barter, there are now workable options to using metaldehyde-based pellets (which can poison dogs, cats and wildlife if eaten in large quantities). For example ferric phosphate pellets, which are harmless to creatures other than slugs, and a range of barriers and traps.

Regulations and proposals

In 1993, the European Union brought in a strict pesticide approval process called The Plant Protection Products Directive. In September 2009, a revision of that directive was agreed, whereby pesticides will now be regulated according to their ingredients rather than just the levels of exposure to the chemicals.

The Crop Protection Association has predicted that some 15 to 20 per cent of currently approved crop protection products will be lost as a result of this revision. Garden pesticides will be also affected by this new legislation, as rejected chemicals will lead to more branded products being withdrawn in the next couple of years.

Did you know?

• Only products approved by the government can be used as pesticides in the garden. That means home-made solutions, made from substances such as washing up liquid, are technically illegal.
• There are currently more than 700 pesticide products by the Chemicals Regulation Directorate (CRD), including insecticides, herbicides and fungicides that are approved for use in the home and garden in the UK. This includes a number of target specific products, such as slug pellets based on ferric phosphate which is harmless to humans, pets and wildlife that are approved by the organic gardening organisation, Garden Organic.
• Recent products withdrawn include the weedkiller sodium chlorate (last date of sale 30 September 2009), and rotenone (last date of sale 10 October 2009), an odourless chemical used as an insecticide, pesticide, and piscicide.

Viewpoint

Guy Barter, Chief Advisor, RHS. "We believe that when used correctly pesticides, insecticides, fungicides and herbicides have a useful role to play in a garden. But gardeners should try other approaches, such as choosing plants to suit the conditions, growing resistant cultivars, using barriers and natural products including biocontrols, first.

There are some situations where no matter how well you garden, plants will get pests and diseases - for example, outdoor tomatoes will almost always get blight in wet summers. This is where intervention is necessary. Early treatment as soon as troubles appear uses much less pesticide. If you do have to use a synthetic pesticide, apply it carefully, according to instructions, and make up slightly less than you need so that washings can be used to treat the last few plants. In many gardens so little is needed that ready-to-use packs are the best option."

What you can do

• Many pests and diseases can be minimised by good gardening practices such as careful feeding and watering, crop rotation, and choosing plants that suit the conditions.
• Use barriers such as mesh against flying creatures and products such as copper tape, rings, grit or mats against slugs and snails.
• Try biological controls such as nematodes which use one living organism to control the pest without harming humans, pets and other beneficial creatures. These work very effectively but require a minimum temperature to work, and are expensive for using on large areas.
• Encourage natural predators, such as ladybirds and lacewings, by creating wildlife habitats and hiding places in your garden.
• Try companion planting to deter pests.
• Choose plant varieties that show resistance to pests and diseases.
• Avoid overfeeding young plants - lots of lush growth will attract slugs and snails.
• Use chemicals as a last resort, making sure you use the right product for the pest, disease or weed. Don't buy more than you need, and dilute exactly as directed on the label. Apply it at the right stage of a pest's lifecycle. Spray in early morning or late evening, when beneficial insects are not foraging. Do not spray if it is windy or about to rain.
• Store chemicals in their original containers in a cool dark place, out of reach of children and pets. Spray surplus diluted product on level, bare soil or over an uncultivated area such as gravel or a driveway, away from drains, ponds or watercourses.
• Contact your local authority to get rid of unwanted or withdrawn products. Check which products are currently legal by calling the Chemicals Regulation Directorate's Plant Protection Products Information section on 01904 455775.