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A Guide to Organic Pesticides

March 6, 2008  By Michael Lascelle

The market for domestic pesticides is rapidly changing across Canada, due much in part to public concerns about possible health risks that have been linked to their use.

 Many homeowners express their ‘No Pesticide’ policy with Sierra Club of Canada signs.

The market for domestic pesticides is rapidly changing across Canada, due much in part to public concerns about possible health risks that have been linked to their use. As of July 2006, there were 119 municipalities, which had adopted bylaws restricting pesticide use – in such major cities as Toronto, Vancouver, Montreal, Waterloo, and Halifax. The province of Quebec has even drafted its own ‘Pesticide Management Code,’ which bans domestic lawn-care products containing herbicides, as well as several common pesticides. This matter has even gone as far as the Supreme Court of Canada, where Toronto’s bylaw against the ‘cosmetic-use’ of pesticides survived a serious legal challenge.

So what does this all mean to us, at the local garden centre level? It means that many of the domestic pesticide products that we have sold to our customers over the years are coming off-market, and we need to be able to offer some alternatives. Organic pesticides, beneficial insects and physical controls all provide viable pest-control options, the only problem being that not all of us are familiar with them and, as a result, many garden centres may not stock these items. These products have great sales potential and when marketed properly, may provide more profit for you than those earned through traditional pesticide sales. With that in mind, here is a brief overview of the new ‘organic’ pest-control arsenal.
Biological Controls:
Biologicals represent the cutting edge of organic pest control and for the most part, have only recently been widely available through garden centres for public use. The basic premise is to use one bug to kill another, without adversely harming the natural environment. Most are highly perishable products that need to be ordered on demand and in season – which means that you will also need some knowledge about the life cycle of local pests, in order to understand when the biological control should be applied. For the most part, your supplier and their sales representatives will be able to guide you in regards to timing and availability. Here is a small sampling of some of the most common beneficial insects and biological controls:


• Encarsia formosa – A small parasitic wasp, which preys on several species of whitefly.
• Hippodamia convergens – Commonly known as ladybugs, both the adult and larvae stage of this insect feed primarily on aphids.

• Phytoseiulus persimilis – A red predatory mite, which feeds on all stages of spider mite.
• Heterorhabditis and Steinernema – Nematodes are naturally occurring organisms, which are useful in the control of turf grubs, wireworms, orchard pests and cutworms.

• Bacillus thuringiensis var. kurstaki – BTK is a beneficial bacteria, which will safely kill leaf-eating caterpillars without adversely impacting the environment.

• Amblyseius cucumeris – A beneficial mite that feeds on small thrips larvae while foraging leaf surfaces.

Physical Controls:
Many physical controls are organic in nature in that they can negate the use of chemical pesticides. When used properly, they are highly effective and can represent an important alternative for those customers who may resist the use of all pesticide products – be they chemical or organic.

• Yellow Sticky Traps – These coloured paper strips with adhesive on both sides, attract and control whitefly, thrips and fungus gnats.

• Copper Strips – Copper in a thin tape form, used as a perimeter barrier against slugs and snails – which will not cross it due to the resulting chemical reaction.

• Reemay Cloth – A thin white cloth commonly used as floating row covers over carrots, to control carrot rust fly maggots.

• Sticky Paste – This substance is used primarily as a barrier on the stems of shrubs and trees, to control wingless female moths (by preventing them from laying eggs), weevils and ants.

• Wasp Traps – These ‘one way’ traps can be hung near outdoor eating areas to control persistent wasps, which are attracted to the sugar water bait and are unable to exit.

Organic Pesticides:
If you were to look up the definition of ‘organic’ in the Webster’s New World Dictionary, you would find multiple meanings, ranging from ‘derived from living organisms’ to ‘grown with only animal or vegetable fertilizers’ and ‘of any chemical compound containing carbon.’ Defining organic pesticides can be equally difficult, as there are many organic growing standards and certification bodies in Canada, each with their own set of criteria. We should probably only concern ourselves with those bylaws restricting pesticide use, which can vary from city to city.

More progressive bylaws, such as those in Vancouver, allow pesticides based on a list of active ingredients – most of which have a low environmental impact and present few health risks to humans.

We should also become familiar with these active ingredients, in order to keep our customers informed – and when you want to know which active ingredient is being used in the organic pesticides you sell, you need look no further than the container label. The guarantee lists the active ingredient along with the percentage of the product – so you tell your customers exactly what they will be applying and its relative strength. Here is a listing of common active ingredients used in organic pesticides:

• Acetic Acid – Concentrated vinegar used as a non-selective herbicide, sometimes combined with citric acid. Toxicity depends on active ingredient percentage, with concentrations of over 11 per cent capable of causing burns or skin irritation.

• Boric Acid – A stomach poison for ants and other crawling insects, derived from natural borax deposits. Low toxicity to people and wildlife.

• Corn Gluten – A byproduct of corn milling used as a pre-emergent, granular herbicide on turf and planting beds. Non-toxic to people, wildlife and fish.

• Diatomaceous Earth (Silicon Dioxide) – A finely ground fossil used in a dust form for structural pests, slugs and other insects. Non-toxic to people, wildlife and fish.

• Dormant and Summer Oils – Refined mineral oils used to smother over-wintering insect eggs and persistent pests, such as mites and mealybugs. Not compatible with all plants.

• Insecticidal Soap – Biodegradable fatty acids, useful as a contact pesticide on a broad range of insect pests. Fatty acids are also formulated as non-selective herbicides. Very low toxicity to people. Non-toxic to fish and wildlife.

• Iron or Ferric Phosphate – A food-grade dietary supplement used in slug and snail baits. Naturally found in soils, but not in the high concentrations used here. Non-toxic to people, wildlife or birds.

• Lime Sulphur – A calcium-sulphur compound used in a liquid form to control fungal diseases and some pests, usually as a dormant application. Low toxicity to people and mammals.   Non-toxic to fish and birds.

• Pyrethrin – An extract of Pyrethrum daisies, useful as a contact pesticide on a broad range of insect pests. Low toxicity to people and wildlife. Toxic to fish – keep away from streams and ponds.

• Sulphur – A natural element sold in liquid, dust and wettable powder form to control fungal problems and some mites. Low toxicity to people and mammals. Non-toxic to fish and bees.

As you can see, organic pesticides are not just a last resort or products we turn to in the absence of chemical alternatives. They are safe, environmentally sustainable products that represent a growing market, one that is only going to get stronger as cities across Canada adopt bylaws that affect our gardens, and the products we use to maintain them.

Michael Lascelle is a working nursery manager, author and certified arborist based in British Columbia.

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