Organic & Natural Pest Control

I offer full organic pest control services for trees and shrubs. My services include dormant oil, herbicide, fungicide and insecticide application. I offer Integrated Pest Management (IPM), in accord with City of Toronto by-laws, and the International Society of Arboriculture (ISA) guidelines.
D. Andrew White M.Sc. - 05/05/2011

Ontario's Cosmetic Pesticides Ban

On April 22, 2009, the Government of Ontario issued a ban on cosmetic pesticides. This Ontario Regulation 63/09 overrides municipal pesticide bylaws, and thereby establishes one clear set of rules for all Ontarians. This act bans the use of a number of pesiticides that would otherwise be used ford for purely cosmetic reasons. Special exemptions can be made for health and safety reasons, as well as many argicultural uses. Explicit permission is required for the use of these substances - or organisms.

Several 'Classes' of pessticides are regulated under the Pesticide Classification Guidelines for Ontario:

(A) Classes 1 to 4 are banned from casual use. These include the stronger synthetic chemicals, such as the 2,4-D group. This list includes pesticides only for use in argiculture, or for emergency pest control.

(B) “Classes 5, 6 and 7 are pesticides designated under the PCPA as pesticides of the Domestic Class to be distributed primarily to the general public for personal use in or around their homes.” These include many formulations of: acetic acid, 'dormant' oils, several kinds of animal repellents, some household insecticides, household copper-sulphur based fungicides, pyrethrum or pyrethrins, wood preservatives, some mouse and rat poisons and even the herbicide glufosinate ammonium - within strict limits.

(C) Classes 8 to 10, are more-or-less banned from casual cosmetic use. These include stuff like rotenone, diquat, malathion and dicamba.

(D) “Class 11 pesticides require a “green” notice sign be posted for the purposes of providing public notice when products containing these ingredients are used by any person on non-residential area land and by a licensed exterminator on residential area land in performing land exterminations.” These include some formulations of: boric or boracic acid, citric acid, diatomaceous earth, certain fatty acids, ferric phosphate, insecticidal soap, pepper based animal repellents, some sulphur based fungicides, fungi such as Sclerotinia minor, Bacillus thuringiensis bacteria and presumably some kinds of nematodes.

Pesticide By-Laws in Toronto

The City of Toronto has passed a bylaw restricting the use of pesticides within the GTA. This by-law No. 456-2003 came into effect April 1, 2004. The by-law shall be fully implemented, and enforced, by the end of 2005. Certain low risk pesticides will be allowed. These include pesticides with the following active ingredients: insecticidal soaps, 'dormant' oils or mineral oils, diatomaceous earth, ferric phosphate, Bacillus thuringiensis bacteria, nematodes, boric or boracic acid, pyrethrum or pyrethrins, fatty acids, or sulphur based fungicides.

Certain exception shall be made for the control of major infestations, or for the sterilisation of wood products, or in the case of a pest which poses a public health hazard. However, the Ontario pesticide ban supersedes the Toronto bylaw - except perhaps where the Toronto bylaw is more strict!

'Organic' Pesticides

I have received many questions about 'organic' or 'botanic' pesticides. Therefore, I have assembled some information about botanic pesticides: nicotine, pyrethrum, rotenone, ryania, sabadilla and neem. And also some information about biological control agents: Bacillus thuringiensis, Beauvaria bassiana, Metarhizium anosopliae and Verticillium lecanii. I hope that this precis may answer some of the questions that people have.

Apologetics for Botanicals

If one searches the literature for organic pesticide apologetics, one generally finds vague metaphysical statements, philosophical rhetoric, or general theories of physiological adaptation to 'natural' chemicals. Just as commonly, much of the literature gives no real justification at all for preferring 'natural' pesticides over artificial ones. The label 'natural' is presumed to speak for itself. Since 'natural' does not equal 'harmless', some scepticism is called for. Basically many plants are toxic - an adaptation to avoid being eaten. A ramification of this is that some plants are not particularly good for one's well-being.

But there is some justification for fearing some of the synthetic pesticides. These chemicals are formulated purposely to be poisons. Furthermore, they are often applied in vast quantities. This adds up to a lot of poison. In some cases the toxicity of these pesticides, to non-target species, has been known since the 1950s. An example could be the near obliteration of Salmon in the Miramichi River, in New Brunswick. This salmon die-off was the inadvertent result of DDT spraying to control spruce budworms. And it has likewise been known since the 1950s that over-use of pesticides can result in the elimination of natural pest controls. A classic example, from Nova Scotia in the 1950s, was the spraying of apple orchards with DDT for codling moth control. This resulted in a resurge in parasitic mites. The DDT killed off the insects that preyed on these mites. As a result the mite populations exploded, and the apple harvests were no better than before (Carson 2002).

On the other hand, farming without any pest control is just not workable. Since there must be some pest control, it is incumbent upon agricultural science to find more balanced methods of controlling pests.


Nicotine is a natural insecticide from Nicotiana spp. (tobacco) stems and leaves. Have you ever wondered why the old folk insecticide of 'cigar buts soaked in water' is NOT recommended as an insecticide?

Advantages: Very toxic to insects as a contact insecticide. On a per dose basis it is 30 times as toxic as rotenone. Useful for knocking down chafers and other leaf eating insects in an emergency.

Disadvantages: On a per dose basis it is 30 times as toxic as rotenone. Basically, nicotine is considered too toxic, to birds and mammals, for some agricultural uses or for general garden use. The use of nicotine is discouraged by toxicologists. For certain applications the use of nicotine, a 'level 1 insecticide', is actually illegal.


Pyrethrum is an extract from Chrysanthemum cinerariifolium daisies. Several different kinds of pyrethrins are the active ingredients.

Advantages: Pyrethrum extracts have very low toxicity to mammals. If they do not kill insects outright, they 'flush out' insect pests. Pyrethrins have been intensively studied by toxicologists, therefore their Lethal Doses (LD50s) for various target and non-target species are well known. Pyrethrins also breakdown rapidly after application. They breakdown so quickly that they are widely considered safe for use on fruits ready for harvest.

Disadvantages: Pyrethrins 'knockdown', 'flush out' or kill most insects, 'beneficial' or otherwise. This can leave the plants open to re-infestation in a milieu devoid of natural predators. It is toxic to bees and fish.


Rotenone is extracted from Lonchocarpus spp. roots, it can also be derived from Derris spp..

Advantages: Rotenone is an effective killer of aphids, thrips, caterpillars, sawflies, beetles and mites. (It is especially effective on leaf eating insects.) Rotenone breaks down rapidly, within days.

Disadvantages: Rotenone is more acutely toxic than many synthetic pesticides. Chronic exposure to rotenone has been tentatively linked to Parkinson's disease in humans. It is fairly toxic to mammals and birds. It is very toxic to fish. (It has been used for centuries to stun fish.) It is not quick acting and may take several days to actually kill insects and mites, after they ingest it.


Ryania is an extract from the roots of Ryania speciosa.

Advantages: Ryania is effective in controlling codling moth caterpillars, leaf eating beetles and thrips. It has relatively low toxicity to mammals.

Disadvantages: Ryania also kills 'beneficial' insects as well as 'pests'. It breaks down fairly slowly. Therefore, it should not be used on fruits near harvest time.


Sabadilla comes from the roots of Schoenocaulon officinales.

Advantages: Sabadilla is effective at controlling sucking bugs, leaf eating caterpillars, beetles and thrips. It is not very toxic to mammals.

Disadvantages : While of low toxicity to mammals, it is still a lung irritant. It can cause depression of blood pressure in mammals.


Neem is an extract from the seeds of Azadirachta indica trees.

Advantages: Neem interferes with the hormonal system in insects. It causes insects to moult improperly, thus killing them. Neem works best against chewing insects.

Disadvantages: Sucking insects such as aphids are less susceptible to neem. It has been recently approved by the US EPA, like any new pesticide change in status is possible.

Biological Control Agents

Biological control agents (BCA) are living organisms that feed-on or kill pest species. These are usually sprayed with a liquid carrier to carry a the agents in their resting spore stage. The spores in contact with the host insect hatch, and infect the insect. Some agents, like Bacillus thuringiensis have been used for a long time. Other BCAs have already become naturalised. For example, the Australian Rodolia cardinalis ladybird-beetle, which eats citrus-scale, is now well established in the Americas! Others are newer on the market. In general, most farming economies have been slow to adopt BCAs. Only Cuba has experimented with BCAs on a large scale.

Some BCAs are actually small animals that eat insect or mite pests. Among the well known types of insect BCA there are the Trichogramma wasps. These wasps lay their eggs on caterpillars and cutworms. The eggs hatch and then devour the larvae from the inside. This can kill enough of the larval pests to significantly reduce the overall pest population. Consequently, Trichogramma wasp release is a fairly successful BCA method. The wasps are commercially avaialble on a large scale. Predatory nematodes are another BCA sold commercially. These are somewhat out of favour with gardeners, as the nematodes also kill beneficial insects. All BCAs have their own advantages and disadvantages.

Advantages: Most fungal and bacterial BCAs are affordable for farmers and foresters. Most do not cause great problems in non-target ecosystems, as their efficacy is due largely to the high initial spore concentration in the spray. These species are generally present in the wild surrounding the farm or forest, but in smaller concentrations. Secondary generations of the BCAs generally fall to levels similar to the wild populations.

Disadvantages: Most BCAs must be applied at the opportune time. Weather conditions and poor timing can all diminish the efficacy of BCA treatments. It is possible that non-target ecosystems can be disturbed by BCA spillover. The less specific of the BCAs can also kill off natural predators and other beneficial insects and mites.

Bacillus thuringiensis

Bacillus thuringiensis is bacteria that infests a wide range of lepidopteran larvae, i.e. moth and butterfly caterpillars . The bacterium is applied in spore form, in spray form, at an application rate of a 108-109 bacteria per hectare. It has been used successfully by foresters for a few decades, and it is being used increasingly in agriculture throughout the world. New strains of the bacterium have been developed that kill budworns - i.e. sawflies.

Beauvaria bassiana

Beauvaria bassiana is a fungus that is used to control insect pests, such as the banana weevil (Cosmopolites sordidus), the sweet potato weevil (Cylas formicarius), and the rice pest Lissorhoptrus brevirostris. It is applied in liquid formulation at a rate of 1-3 x109 spores per hectare.

Metarhizium anisopliae

Metarhizium anisopliae is a fungus which is used to control banana weevil (Cosmopolites sordidus), the greater wax moth that inhabits beehives (Galleria mellonella), and several other pests. Its application rate is best at high concentration of 1011 - 1012 spores per hectare.

Verticillium lecanii

Verticillium lecanii is a fungus that is used specifically to control the sweet potato whitefly (Bemisia tabaci). Its application rate is 1011 - 1012 spores per hectare.

Dormant Oil


Winter oil, or dormant oil, is a mixture of phenol compounds and tars in an oily suspension. The oils are formulated for killing the over-wintering eggs, nymphs or pupae of insects. Dormant oil is, in effect, an insecticide applied in anticipation of a future pest infestation. The oil is fairly effective in controlling: aphids, psyllids, scale insects and mealybugs. Dormant oils are allowed under Toronto's new pesticide by-law.

Dormant oils must be not be applied outside of the plant's dormant season. Basically, the should be applied during winter and early spring prior to bud-break. The oils can harm sprouting buds. They also can kill lichens and mosses. They are mildly toxic to mammals. They should be used as directed, and not in excess.



At the present time there are virtually no effective herbicides of botanical origin. (Plants are not generally adapted to killing other plants.) All herbicides that work sufficiently well, and are within basic safety parameters, are 'organic' compounds which are synthetic (i.e. manmade). Glyphosate is a synthetic organic. It is an herbicide that is relatively safe for animals, and very effective at killing plants.

Herbicide Damage

Sometimes one may notice odd symptoms affecting leaf or twig form. These weird disorders cause curls in leaves, pockets in fruit, stunted twigs sometimes along with leaf yellowing or wilt. ‘Curl disorders’ are typically the symptoms of a virus infection. However, if the symptoms afflict many plants of different species, one should suspect herbicide contamination as a possible cause. Virus infections usually affect only a single species. Herbicide poisoning is usually broad spectrum in its influence.

Residual effects of herbicides can adversely affect trees. It often happens that urban trees are weaked or even killed by “weed & feed” type fertiliser / herbicide mixes. These mixes contain a standard NPK fertiliser and also some 2,4-D for controlling ‘broadleaf weeds’. Sometimes people think that a double or triple dose will kill even more weeds. The excess 2,4-D can injure large broadleaf plants – i.e. trees. This is especially likely after a rain. Rainwater can move the herbicide into a tree’s root-zone. (Occasionally rural gardens and lawns are damaged by herbicide drift from farms.)

2,4-D can cause series of disorders which could be mistaken for viral infections. Glyphosate usually causes yellowing (chlorosis), wilt or death. Often the symptoms of glyphosate damage occur nearest the side of the tree where the herbicide has been applied. This herbicide sometimes kills whole stems of a shrub. While less likely to kill a whole tree, glyphosate can kill saplings if the dose is high enough.


Glyphosate (N-phosphonomethyl glycine) is an complex compound which interferes with specific steps in the photosynthetic process. It is absorbed systemically by plants, and if in sufficient dose, it kills the plants within 48 hours. Glyphosate denatures on exposure to dirt, air and sunlight. It does not persist in soils, and it is not suitable for sterilising soil. Experimental evidence suggests that glyphosate is less toxic to animals, per unit dose, than are many other common household products. Glyphosate is non-selective, it kills monocots and dicots with similar vigour. Glyphosate is available in several formulations, under different trade-names: AquaNeat, Glyfos, Roundup and WipeOut, to name but a few. Glufosinate ammonium is another related formulation. It is less toxic to animals than glyphosate, and is slightly less restricted for use in Ontario.

Glyphosate Resistance

Perhaps not surprisingly, the overuse of glyphosate has resulted in intense selection for resistance. Ragweed, horseweed and Johnsongrass have all developed varying degrees of glyphosate resistance. Probably many other weed species shall evolve glyphosate tolerance - if the herbicide continues to be overused.


Another common synthetic herbicide is 2,4-D (2,4-dichlorophenol). It was part of the defoliant Agent Orange once used by the U.S. military. Herbicides with 2,4-D as the active ingredient are more toxic to dicots than they are to monocots. It does not easily kill turf grass, nor cereal crops. However, 2,4-D does readily kill most 'broadleaf' weeds. Experimental evidence indicates that 2,4-D is somewhat toxic to animals.

Acetic Acid

Acetic acid, i.e. vinegar, can be used to ‘burn’ plants. A solution of 20 % to 50 % aqueous solution of vinegar makes a good broad-spectrum plant killer. (Only the strongest solutions work in reality.) The acid quickly neutralises in most soil types, hence it has little residual effect on soil pH. Like glyphosate it can be spot-sprayed directly on the target weeds. It is not quite as effective as glyphosate. However, acetic acid is allowed under Toronto’s bylaws.


jack-o-lantern fungus

There are synthetic 'organic compounds' for controlling fungi. Bupirimate, Captan and Carbenazim are just a few examples. Currently there are no botanical fungicides that are good enough for general garden use.

Copper Fungicides

The safest fungicides are sulphur or copper based. It is these inorganic fungicides which are to be allowed under Toronto's new pesticide by-law. Copper oxychloride, and copper sulphate are fairly effective fungicides. Copper sulphate mixed with ammonium hydroxide forms the ever popular Bordeaux Mixture, which is quite effective.

Copper based fungicides are useful as contact killers of growing fungi. They are not so effective against fungal mycelia which have penetrated the plant tissue. The element copper is fairly toxic to plants in high doses. Copper based fungicides can harm plants if applied incorrectly. (Some copper compounds can be toxic to mammals also.) Also, fungicides in general must be applied during a 'windows of vulnerability', otherwise the fungicide may be ineffective. Often when home owners notice a sign or symptom of a fungal disease, the damage to the plant has already been done.


Adler, Jerry. 2011. The Growing Menace from Superweeds. Scientific American. 304 (5): 74-79.

Blaustein, Andrew R. and Johnson, Pieter T.J. 2003. Explaining Frog Deformities. Scientific American. 288(2): 60-65.

Carson, Rachel. 2002. Silent Spring. 40th Anniversary Edition. Houghton Mifflin Company. New York.

Cranshaw, Whitney. 2004. Garden Insects of North America. Princeton University Press. Princeton.

Gribble, Gordon W. 2004. Amazing Organohalogens. American Scientist. 92 (4): 342-349.

Otto, Stella. 1993. The Backyard Orchardist. OttoGraphics. Maple City. 194-198.

Phillips, Kathryn. 1995. Tracking the Vanishing Frogs - an ecological mystery. Penguin Books.

Rosset, Peter and Benjamin, Medea (Eds.) 1994. The Greening of the Revolution - Cuba's experiment with organic agriculture. Ocean Press. Melbourne. 33-50.

Royte, Elizabeth. 2003. Transsexual Frogs. Discover. 24(2): 46-53

Schultz, Warren. 1999. Natural Insect Control - the ecological gardener's guide to foiling pests. Brooklyn Garden Inc. Brooklyn.

Botanical Commentaries

Web page designed by D. Andrew White M.Sc.©
MM anno domini