Organic & Natural Pest Control
D. Andrew White M.Sc. - 09/09/2008
One day while I was spraying turf grass, my muse said to me: ‘grass is not worthy of this.’ Turf grasses are not crops and neither feasts nor famines depend upon them. I can appreciate the need for pesticides in agriculture, or to kill-off serious infestations of forestry pests. However, this argument is too far stretched to be applied to ornamental plants. Most pesticides are toxic to not-target species. Humans, pets and songbirds are included in this list of non-target species. Urban trees, gardens, and turf grass, are not worthy of the serious risk that the stronger insecticides pose. In a phrase: I basically agree with the new Toronto anti-pesticide bylaws. I am licensed, but I only spray trees for serious cases of fungal infection - sometimes, and I spray dormant oils in advance of pest outbreaks. And I, like many arborists, don't care much about turf grass.
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.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: 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. 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.
'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, neem and the meaning of LD50%. 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 generallty finds vague metaphysical statements, philosophical rhetoric, or general theories of physiological adaptation to 'natural' chemicals. Just as commonly, much of the literature gives no justification at all for prefering 'natural' pesticides over artificial ones. The label 'natural' is presumed to speak for itself. Since 'natural' does not equal 'harmless', some scepticism is necessary.
The general theory of physiological tolerance to certain chemical families, is the most concrete of justifications for the use of natural pesticides. This theory states that animal bodies are more able to breakdown chemicals that occur in nature than chemicals that do not occur naturally. More specifically, organism are more likely to tolerate chemicals that are similar in composition to those they encounter in nature.
Advantages: Botanical pesticides are organic chemicals composed of hydrogen (H), and the lighter elements with outer electrons in p-orbitals. These include carbon (C), nitrogen (N), oxygen (O), phosphorus (P) and sulphur (S). The halogens chlorine (Cl) and fluorine (F) are not as common in botanicals, but they do occur. These elements form mostly covalent bonds, with carbon forming being the crucial ingredient. The 's-orbital' metals magnesium (Mg), potassium (K), and calcium (Ca) can occur in botanical compounds. The heavier 'd-orbital' elements, which tend to form ionic bonds, are rarely present in these compounds. Consequently, the heavy metals, which are often toxic, do not normally occur in botanicals. Most botanicals are digested by some organism or another, and most chemically 'denature' (breakdown) with prolonged exposure to heat, oxygen and sunlight.
| H | II. | III. | IV. | V.. | VI. | VII | He |
| Li | Be | B | C | N | O | F | Ne |
| Na | Mg | Al | Si | P | S | Cl | Ar |
| K | Ca |
Synthetic pesticides are increasingly being banned by government legislation.
In general, organic chemicals are not slated for these prohibitions (this may change).
Disadvantages:
As rated solely on their ability to kill pests, most botanical pesticides are rated 'fair' to 'poor' by commercial orchardists. None are considered 'excellent' or even 'good'.
Most botanical pesticides are chemicals produced by plants to discourage herbivorous organisms.
Their natural function in plants is to be toxic.
(For example,
the African plant Dichapetalalum cymnosum produces fluoroacetic acid, i.e. the ultra-toxic pesticide 1080!)
Insects and mites have many physiological similarities to mammals.
Therefore, it is not surprising that botanical pesticides are usually toxic to mammals also.
Most botanical pesticides are either general biocides, or general bio-irritants.
They are generally not very specific in their action.
There are very few botanical inscticides that target only 'harmful' insects.
Artificial compounds can be test and modified such that they are tailor made to have low toxicity to non-target organisms.
This is why pesticides of high specificity tend to be artificial compounds, not natural ones.
Are Pesticides Necessary?
Increasingly people are questioning the wisdom of pesticide use. Pesticides are, after all, poisons released into the environment. The deleterious effects of these poisons on wildlife and humans are well documented. Having said that, it is also true that the newer high-tech pesticides are far less toxic to non-target organisms than were old fashion pesticides. Almost all of these high-tech pesticides breakdown after a few days and loose their toxicity. These safety features were designed on purpose. Political pressure from environmental activists has been one of the main motivations for developing these advanced pesticides.There are many reasons to avoid pesticide use. However, it would be difficult to realistically envision a highly populated world like ours without pesticide use. Farmers use pesticides because they believe, based on solid evidence, that they need them to stay in business. On a global scale: too many farmers exist on slim profit margins, in competitive markets. Before pesticide use, herbivorous arthropods and competing weeds reduced yields by about a third. Organic farmers have found that this is still often true. Yields in modern 'organic farms' are usually significantly less than they are for farms that use pesticides. In the long term, pesticide use should be reduced. The question is: how do we accomplish that goal fairly and justly?
LD50%
Lethal Dose 50% (LD50) is the amount of a substance necessary to kill 50% of a particular test species in seven (7) days. Its measure is translated into milligrams (mg) of active ingredient per kilogram (kg) of animal body mass (mg/kg). Which is to say that LD50 is a measure of acute toxicity, ie short term poisoning. The test animals are usually: mice, rats or rabbits.Pesticides are indeed tested on animals! (Another reason to consider the ethics of pesticide use.) LD50s are, obviously, not based on tests directly involving human subjects. Therefore, the actual human LD50s of most pesticides are merely surmised. Furthermore, chronic toxicity in long-lived animals is nearly impossible to test in the laboratory. Most test animals are not long-lived species. Humans are a long-lived species. Chronic toxicities of chemicals are therefore not as well documented as are LD50s. This is true of all chemicals, natural or artificial. There is no valid philosophic or scientric reason to suppose that 'botanicals' have no chronic effects, just because they are 'natural'.
Nicotine
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
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
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
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
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
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.
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 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 is a fungus that is used specifically to control the sweet potato whitefly (Bemisia tabaci).
Its application rate is 1011 - 1012 spores per hectare.
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.
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.
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.
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, 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.
This has been claimed that extra calcium can be used to suppress broadleaf weeds, and boost grass.
This has been exaggerated into the idea that calcium is some sort of ‘organic’ weed control.
Actually, extra calcium merely tends to give grass a competitive edge over some other weed species.
Calcium merely boosts the grass’s growth at the expense of some dicotyledonous weeds.
The boost only works as long as there is extra calcium for the grass to absorb.
To maintain the lush grass, one must re-apply calcium fertiliser year after year.
Despite its relative safety, the City of Toronto includes glyphosate among the herbicides restricted under its by-law # 456-2003.
Herbicides containing 2,4-D are also to be restricted.
By the end of 2005, Toronto's gardeners shall need to rely more on manual weeding!
Weeding looks as if it is here to stay.
So why not make less work for yourself?
There are non-herbicide methods of reducing weeds in ornamental gardens:
One does well to remember that ‘cultivating’ the soil is largely a mindless tradition.
Turning the upper layers of soil largely results in drying out the root zone.
In some soil types this accelerates in the leaching of potassium and other ions.
Furthermore, turning soil buries any weed seeds that might otherwise have died in the sunlight.
Turning bare soil is done mostly because it has long been expected of gardeners.
One could cultivate for a quick weeding, or for breaking up hard soil, or for initial flowerbed preparation.
In other words, not much cultivating needs to be done after spring.
It is better to crowd plants into the flowerbed than to waste precious hours turning bare soil.
This time could be better spent doing more productive things.
If you must improve the soil, add and mix in top soil or compost.
Don't add peat moss unless the soil is extremely clayey.
Peat is not a fertiliser.
It is a porous material which does help to hold water in the soil.
If one has a loamy soil, adding peat is hardly necessary.
Natural sources of peat moss are becoming ever more scarce.
Peat builds up in bogs very slowly.
It is currently being mined much faster than it is being renewed.
Therefore, if one wants to conserve our natural resouces, boycott buying peat.
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.
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.
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.
Blaustein, Andrew R. and Johnson, Pieter T.J.
2003.
Explaining Frog Deformities.
Scientific American. 288(2): 60-65.
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.
Beauvaria bassiana
Metarhizium anisopliae
Verticillium lecanii
Dormant Oil
Herbicides
Glyphosate
2,4-D
Acetic Acid
Calcium
Weeding
A - Crowd out open soil by tightly planting flowers. Leave less room for weeds.
B - Plant tightly spaced perennials to crowd out weeds.
C - Use mulch to cover open areas, about 6 cm thick.
D - Ground-tarps, overlaid with mulch or gravel, can also restrict weeds.
E - Hire a gardener to waste your money on cultivating.
Cultivating Dirt
Peat Moss
Fungicides
Copper Fungicides
Herbicide Damage
References
