WiseGardening Aims
WiseGardening aims to show the risks of garden chemicals to bees, birds, frogs and other species when we try to control pests, disease and weeds and help you make informed choices.
Why Use WiseGardening?
The broad community which uses chemical garden products has a right to know risks associated with their use. These products can affect:
- Users if they come into contact with the product or breathe in vapours – some products are quite toxic.
- Species that visit or live in our gardens – birds, bees, fish, worms, frogs and a range of mammals, such as pets, especially if the chemicals persist in the soil.
- Aquatic species as well as fish – if the chemicals can be washed through the soil winding up in streams and other waterways they may harm not only fish, but also other aquatic organisms.
So knowing which product to select, when faced with a plethora of ‘plantastic products’ in the local garden centre, or knowing if we should still use old products with stained labels stored in our garden sheds, can be very daunting. In order to minimise these risks we all need to know what they are.
WiseGardening has been developed to help all of us achieve international sustainable development goals through reducing some of the impacts that our society has had on the planet. This Australia-first guide aims to be rigorous in its ratings so it is based on publicly available evidence-based, scientific information from university and government sources. SGA has assessed then rated over 850 garden chemical products commercially available in Australia. Because SGA prefers to avoid using chemicals, we also present alternative non-chemical methods which we recommend as the first line of defence for garden problems, but we recognise that there are times when a chemical product is a necessary choice.
Similar guides are available for specific areas overseas, such as Europe or the USA (www.growsmartgrowsafe.org) but these are not tailored for products and formulations used in Australia.
As you might expect, since these products are termed pesticides and weedicides where the suffix “icide” means “kill”, many chemical products, as well as killing their targets, carry risks to users and other species on our amazing planet – even when they are used very carefully.
Manufacturers alert users to these risks on their product labels, instructions for use and Safety Data Sheets. However, when consumers buy products they may not consult these sources in-store to compare products and may not even read or understand the advice provided before using the products. WiseGardening provides an easy way of comparing products for their impacts on humans and other species on the planet.
WiseGardening does not:
- Provide comment on product effectiveness in achieving its purpose, or
- Endorse, or condemn any product, manufacturer, brand or supplier.
Principles Underpinning WiseGardening
- Transparency – We aim to augment the availability of information that manufacturers provide about their garden products. To this end, WiseGardening uses publicly available information from many sources. (See Our Ratings and Assessment Process)
- Accuracy – This means that assessments are systematic and based on robust scientific research from reputable sources. However, sometimes this information is unavailable due to commercial considerations and sometimes due to out of date or incomplete information. Where little or no information about a product or ingredient is available this is indicated in WiseGardening.
- Independence and objectivity – No preference to any products or for any manufacturer is given.
- Comprehensiveness and inclusiveness – We aim to include all chemical garden products available in Australia for non-agricultural use. Products available in other countries are not included since, elsewhere, they mostly differ in names and ingredients. We have also not restricted assessments to commercially manufactured products and have included alternative mostly non-chemical approaches. If a product is missing it is not intentional; we aim to include all relevant products. We have not considered home-made mixes of household chemicals since it is not possible to obtain any accurate information about ingredients used in these preparations.
- Currency – The assessment is routinely updated and products are frequently assessed to determine if their ingredients, or details in the product description, have changed. Information sources for ingredients are also frequently checked to ensure the latest publicly available scientific assessments are used. As products are often discontinued by manufacturers, we retain these products in our database so that assessments can be made of new products against discontinued products across product types. Sometimes, new products have the same name as a discontinued product but have a different composition. We aim to ensure that assessments of current products are no older than 1 year.
- Ease of Use – The rating system should provide users with data that is accessible, able to allow comparison and easy to use. Data entry for WiseGardening has been structured so that assessment is performed automatically, drawing on ingredient information within the database.
- Compatible with UN Sustainable Development Goals –
- Goal 3: Ensure healthy lives and promote well-being for all at all ages
- Goal 12: Ensure sustainable consumption and production patterns
- Goal 13: Take urgent action to combat climate change and its impacts
- Goal 15: Sustainably manage forests, combat desertification, halt and reverse land degradation, halt biodiversity loss
- Fostering productive change – encouraging the community and industry, through education, to engage with the change required to achieve a safer and more sustainable world.
Who are We?
Sustainable Gardening Australia (SGA) is a not-for-profit, non-government organization with a strong interest (passion) for enabling gardeners to grow their own food, protect their health and that of the planet and all that is naturally on it. It has charitable status under the federal government’s Register of Environmental Organisations and is registered with the Australian Charities and Not-for-Profit Commission (ACNC).
WiseGardening was initiated over 20 years ago as a collaboration between SGA, Paul Gibson-Roy from Burnley Horticultural College (now part of the University of Melbourne), the garden centre Bulleen Art and Garden and local government.
Since 2016, our SGA team has further developed and refined WiseGardening to make it available as part of our web presence. Development has been supported by a 1 year grant from the Telematics Trust as a project to provide community education.
The Team
Dr. Sharron Pfueller (biochemistry, cell biology, environment, sustainability), Dr. Colin Allison (chemistry, environment, climate change, database development), Angelo Eliades (horticulture, permaculture, toxicology), Bridey Oliver (horticulture), Jane Rollinson (horticulture, information mapping), Michelle Dyason (natural methods of pest control).
For full details of our methodology please see Our Assessment and Rating Process.
Who Might use WiseGardening?
Intended users of WiseGardening include home gardeners, managers of Parks and Reserves such as local government, those who maintain public green space, community gardeners, those concerned with human health and natural life on the planet.
WiseGardening Assessment and Rating Process
The WiseGardening Assessment and Rating Process is dedicated to continuous improvement of methodology to accurately assess risks of chemical garden products and to openly and honestly inform users of them.
What Risks Do We Assess?
Products and their ingredients are assessed for risks to:
- Humans and other mammals
- Bees and other beneficial insects
- Birds
- Fish and other aquatic organisms
- Frogs
- Earthworms
Other properties of the ingredients are assessed for:
- Mobility i.e. the likelihood that they will be transported into streams or other waterways during irrigation or rainfall
- Persistence in soil
- Whether they have been reported as carcinogenic, endocrine disruptors or genotoxic.
What data have we used?
Criteria for use of data
To be used in the rating system, data needed to be:
- Evidence-based, i.e. scientifically assessed or estimated
- Publicly available via websites and other documentation
- Independent and impartial
- Reputable, i.e. academic research institutions and government instrumentalities whose task it is to ensure registration of products, setting safety standards and protecting public and environmental standards.
Sources
Date is obtained from a wide variety of publicly accessible sources, including (but not limited to):
- Risk assessments of product ingredients in the Pesticide Properties DataBase (PPDB) created by the Agriculture & Environment Research Unit (AERU) University of Hertfordshire, Hertfordshire, UK. These assessments include both active ingredients and others that may also present in the product if known.
- The Standard for the Australian Uniform Scheduling of Medicines and Poisons (SUSMP) rating,
- Information from the Australian Pesticides and Veterinary Medicines Authority (APVMA),
- Environmental Protection Authority USA’s Toxnet database , in particular https://pubchem.ncbi.nlm.nih.gov/ and https://pubmed.ncbi.nlm.nih.gov/
- Product labels and manufacturers’ websites – too many to list. How much information is available there varies greatly.
- Safety Data Sheets (SDSs) provided by the manufacturer. However, ingredients that are not considered to be those that are active for the product’s purpose are sometimes not listed by the manufacturer. These ingredients are often described as “secret” or “other” without being named. We assess every named ingredient and where there is a lack of information on product contents we have indicated that with a particular symbol. (See Table of symbols below) .
Assigning Scores
Our assessment of products uses a “point score” system to assess the risks of both overall product features and of ingredients. Higher risk levels yield higher numerical point scores. A final assessment converts these scores into a range of stars starting at one star for the highest numerical score, increasing to six stars for products with the lowest risk scores (see below).
Overall product features
These are assessed from the answers to the questions in table 1.
Table 1
Questions about Product Features | Interpretation |
What is the Uniform Scheduling of Medicines and Poisons (SUSMP) rating? i.e. Schedule 5, 6 or 7* | Higher Schedule ratings indicate more toxic chemicals |
Is the product made from non-synthesised materials? | Products that contain natural ingredients are given lower risk scores than those that are produced by chemical synthesis, often from fossil fuels. |
Is the product pre-mixed and ready to apply? | Pre-mixed products minimize the risk of inadvertent spills i.e. less chance of exposure to high concentrations of ingredients and encourage the storage and use of more manageable quantities of chemicals |
Is the product an aerosol formulation ? | Delivery as an aerosol increases the risk of exposure to toxic material |
Is the product a dust formulation? | Delivery as a powder increases the risk of exposure to toxic material |
Is packaging well designed and robust in relation to its Schedule Heading? | An indicator of the capacity of the packaging to prevent inadvertent exposure |
Is the product a repellent or deterrent in its action? | These have lower risk due to lower toxicity of such chemicals |
Is the product a biological control? | These are living organisms and do not involve manufacture requiring use of energy possibly of fossil fuels. |
- Poisons with a rating of S7 cannot be sold for domestic use.
Ingredients
The scoring system for ingredients is based on the assessment used in the Pesticide Properties DataBase (PPDB) created by the University of Hertfordshire, Hertfordshire, UK. Each ingredient is assessed as either no or low risk, medium risk or high risk as shown in Table 2 and points are allocated to these risks.
Table 2
Question | None or Low | Moderate | High |
What is the level of risk associated with this ingredient? | No symbol | Open Symbol | Solid Symbol |
Note: for soil mobility, persistence and if an ingredient has been reported as a human carcinogen, endocrine disruptor or genotoxic compound, it is shown without a quantitative rating, i.e. with a closed symbol.
Risk is assessed for each item shown in table 3 below:
Table 3. Risks and their Symbols
Risk to Species or Property | High Risk | Moderate Risk |
Humans | H | h |
Other mammals (e.g. pets) | A | a |
Bees & other beneficial insects | B | b |
Worms | C | c |
Birds | D | d |
Fish | E | e |
Frogs | F | f |
Other aquatic species (Invertebrates, Crustaceans, Plants) | G | g |
Other Characteristics | ||
Mobile in soil | M | |
Persistent in soil | P | |
Carcinogenic, an endocrine disruptor, or genotoxic | S | |
Poison S7 | Z | |
Biological Control | W | |
No ingredients were listed for the product | O | |
No risk information available for ingredients from currently available data sources |
– |
|
The product is discontinued | ! | |
Other Choices: A Wise Gardening option | Y | |
The ingredients are still under investigation | ? |
If a product contains multiple ingredients that have different levels of risk for any of its properties the score for the ingredient with the highest risk is assigned. For example, a product with 3 ingredients, one with High impact, one with Low impact and one with no impact, is considered to have High impact. In order to avoid inaccurately assigning a “No risk” score to a product when information about ingredients is not available, both High and Moderate impacts increase the product “score” while Low or No impact do not affect the product score.
Some products with similar ingredient compositions may achieve different ratings because the chemical forms of ingredients may differ and have different associated risks.
Once an overall score is assigned to a product, the score is converted to a simple-to-visualize Star rating where products with a low numerical scores receive a greater number of stars. One star is assigned to products with the highest scores and 6 stars to products with the lowest scores.
Where the product is an S7 poison, 0 (zero) stars are assigned to indicate the product is outside our normal rating system.
If no ingredients are listed for a product (symbol “O”) or no risk information for ingredients is available (symbol “-“), a valid star rating cannot be assigned because of lack of information upon which a rating can be based. For these products, a star rating is replaced by the symbol for a question mark “?“. We are working on obtaining this information from manufacturers and chemical databases.
Where a product is discontinued, if we have existing ingredient information from before the product was discontinued, we provide a risk score.
The assessment system, at this stage, does not include Life Cycle Analysis (e.g. detail of how much energy was used in making the product) including product packaging and whether the product is natural or synthesized from chemical ingredients.
Note about the concentration of ingredients
The manufacturer considers the concentrations of ingredients in their assessment of the product, for example in determining the SUSMP (Poison) rating, however in our assessment we do not consider the concentrations because no assumptions can be made about how much of the product is used, how carefully it is used or whether it has become degraded or has been concentrated by evaporation during storage. WiseGardening considers the risk of the pure ingredients and is thus a conservative assessment.
Disputed ingredient risks
The risks associated with some ingredients are disputed by different studies around the world. Glyphosate is an example of particular interest – see our article on this subject. In such cases SGA has used the current scientifically accepted data, but is recognizes that as further investigations of these ingredients are done, our ratings may change as we regularly update WiseGardening.
Inclusion of non-chemical approaches
SGA has included a range of non-chemical approaches to address problems with garden pests, disease or weeds – these are included as “products”. All information on these approaches has been obtained from publicly available sources. We identify these as “Better WiseGardening Choices” for particular product types.
Updating
All products are periodically re-assessed to ensure that any changes to formulations, packaging or active ingredients have been accounted for. Information about ingredients is updated quarterly through the PPDB database and by literature searches for missing ingredient information as required.
Please remember: the risks documented here and used for rating are important if products are used unwisely. Always use products strictly according to manufacturers’ instructions on labels and associated documentation. If you have further questions about a specific product you should contact the manufacturer and/or retailer.
SGA does not endorse the use of any particular chemical garden products, whether or not they are included in WiseGardening. This information is provided to you so you can make your decisions wisely.
WiseGardening
WiseGardening rates garden chemical products for risks to human health, bees, birds, frogs, pets, earthworms, fish, other aquatic species, soil mobility and persistence. Where information is available, final Star Ratings go from 0 to 6.
Data on products and ingredients used to create WiseGardening are the scientifically estimated and publicly reported risks to the health of humans and a range of other living organisms. Also shown are other important chemical properties. For details of how ratings are derived see Our Assessment and Rating Process
Remember: these risks are very important if products are used unwisely. Always use products strictly according to manufacturers’ instructions on labels and associated documentation.
Notes on Using WiseGardening
WiseGardening is sortable using the Search and Filter boxes. The Search function can show information not visible on this page e.g. particular susceptible pests. For some searches a full word such as “fungus” may not find many choices, but the beginning “fung” will show more because many entries might be for “fungicide”. Therefore, for some searches fewer letters may be more effective.
Note that the ingredient risks are based on pure ingredients so the risks are independent of the amount of ingredient in the product.
Some products with high star ratings still show some ingredient risks or other undesirable product characteristics. These products have received a high star rating because aspects of product packaging or being pre-mixed (i.e. not requiring dilution before use, or having robust packaging) reduce the likelihood of spills which could be harmful.
There are a few products which have ingredient risks about which there is conflicting international opinion. Examples are those containing glyphosate, chlorpyrifos or dicamba. Because we have only used data which is scientifically widely agreed on, these products may have achieved a higher star rating than some people might expect, especially if their containers and mode of delivery render the likelihood of inadvertent exposure unlikely.
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WiseGardening Overview
WiseGardening shows risks of garden chemicals to humans, birds, bees, frogs and other species when you use them to control pests, diseases and weeds and helps you choose wisely.
As estimates of the number of synthetic chemicals in the world continues to grow by 2000 each year from around 144,000, it is worth knowing more about garden chemical products. Many may cause harm to:
- Users – if they spill or ingest them or breathe in the aerosols
- Species that visit or live in our gardens – birds, bees, fish, worms, frogs and a range of mammals such as pets especially if the chemicals persist in the soil
- Aquatic species – if the chemicals can be washed through soil and windup in streams and other waterways they may harm not only fish, but also other aquatic organisms.
In this Australia-first initiative, WiseGardening assesses and rates commercially available garden chemical products (currently over 850 which together contain 413 ingredients) and alternative non-chemical options to help you make informed choices about dealing with garden problems.
If you would like to see what choices there are, WiseGardening is for you!
Better WiseGardening Choices
When trying to address problems with garden pests, weeds and diseases in the garden there are other better WiseGardening choices which don’t require the use of chemical products. We have assembled a range of them below.
Pests – Insects, Snails and Slugs
Pests – Insects, Snails and Slugs
There are many options available to reduce pest numbers apart from using manufactured chemicals that have various risks associated with them. Here are a number of better choices.
Traps
Sticky Insect Traps
Commercial ones are available, but you can make your own following instruction/s on many websites. Hang in locations with problem pests and monitor or replace when necessary. However, some of these may trap beneficial insects.
Snail/Slug (Gastropod) Traps
For snails/slugs, place cardboard/wooden/plastic board or flowerpot on ground in damp spot in garden. After 1 or 2 days lift and remove snails/slugs congregated underneath.
For slaters and earwigs as well as snails ad slugs make a container with holes near the top. Place it so that the bottom of holes is level with the ground – cover to keep rain out. Add beer or sweet liquid and vegetable oil to drown pests. Clear out trap regularly.
Bug Zappers
Plug in to 240v power point to attract and then electrocute insects. Locate these away from food preparation/cooking areas. Please note that the environmental impacts of these are not clear. Although they do not involve spraying chemicals, they may kill beneficial insects and they may use carbon-emitting electricity.
Provide Habitat for Predators
Increase Plant Diversity
Grow a large variety of plant species, herbs and ornamentals, especially those with brightly coloured flowers and those that are umbrella-shaped. This will create an ecosystem of interdependent species which keep each other in balance.
Insect Hotels
These can be home-made and are also available commercially.
Nest Boxes
These can be for birds or bats which use insects as food.
Frog Ponds
If you build a frog pond, the frogs will come and they are voracious insect eaters.
Lizard Sun-bathing Rocks
Smooth rocks in the sun attract lizards which eat insects.
Barriers
Wood Ash
Mounded around the plants you want to protect, wood ash can be an effective barrier. Create a thick layer around plant for protection. Replace when damp or depleted. But make sure that the ash was a result of an essential wood burning activity, otherwise it could be the result of an unnecessary carbon-polluting activity.
Netting
Use 5mm x 5mm (or smaller) netting pulled taut over a frame/structure around the plant.
Corrugated Cardboard
Wrap a corrugated cardboard collar around base/trunk of tree/plant and secure with tape or string. Replace periodically over pest breeding season.
Fruit Bags
Bag fruit individually or in clusters on trees to exclude pests.
Wobbly Fences
Put wobbly wire around plants you wish to protect from possums.
Corrugated Iron on Paths
This deters deer which don’t like walking on surfaces that are unstable and make noise when trodden on. Try to use old recycled iron.
Repellents and Attractants
Companion Planting
This approach aims to use nature to attract, repel, enhance plant health and flavour. For example, planting Winter Cress Barbarea verna effectively attracts beneficial insects and entices the cabbage white butterfly to lay its eggs on the leaves. But the plant kills emerging caterpillars as they try eating it. Marigolds deter the cabbage white butterfly from laying eggs on brassicas as well as repelling root nematodes.
Decoys
Decoy plants may be planted earlier than the main crop to entice insects. They can then be removed and the main crop planted. They can also be planted around the outside of a crop as insects usually start from the outside.
Artificial cabbage white butterflies can deter live ones for some time. They should be moved regularly.
Visual Bird Deterrents
Try hanging moving or reflective materials in trees such as lights, mirrors, reflectors, reflective tape, flags, rags, streamers, lasers, dog/human/scarecrow/large hawk models. These will need to be replaced or alternated since birds quickly become used to them and will resume normal activities such as eating fruit.
Manual
Removal by Hand
Look for pests and use your fingers to squash or remove them.
For snails and slugs pick them up and put in a bucket of water containing soap or detergent. This kills any eggs inside the snails and they can later be composted.
Water Jet or Hose
Hose pests off affected plants – e.g. Aphids can be easily removed and will not return.
Fly Swat
Use swat to squash insect against a hard surface.
Pruning
If it is possible, remove the heavily infested section of the plant.
Beneficial Agents
Domesticated Birds
Allowing ducks, chicken or geese to browse in areas of the garden infested with pests can help control their numbers. Such birds are effective predators of snails, slugs, insects and spiders.
Introduce Predatory Insects or Parasites
It is possible to purchase insects and other organisms which will attack pest insects in your garden from a number of suppliers.
Diseases
There are many options available to reduce plant diseases in your garden apart from using manufactured chemicals that have various risks associated with them. Here are a number of better choices.
Bacteria
Avoid Using Seed Which might be Diseased
Use either certified disease-free seed or, if saving seed from your garden, make sure that the plant you are taking it from is healthy.
Crop Rotation
Don’t grow plants of the same family in the same bed for at least 3 seasons to avoid a build up of pathogens in the soil.
Hygiene
Bacteria survive in infected plant debris/litter, seeds and in soils. They are spread by contact, rain splash, vectors and infected seeds. Before and after harvest, dispose of infected plants/plant parts in sealed plastic bags in bins – do not compost them.
Disinfect gardening equipment (bleach/methylated spirits).
Fungus
Avoid Moisture on Leaves, Especially at Night
Moisture persisting on leaves allows fungal spores to germinate. Use drip irrigation rather than sprayers or employ overhead watering early in the morning so that moisture will evaporate.
Exclusion
Prevent pathogens from entering the landscape by only purchasing healthy, vigorous, undiseased plant material. Refuse to purchase any plants showing any sign of disease or poor health.
Hygiene
Completely remove any plants that are either heavily infested with untreatable diseases (remove as much of the plant & root system as possible as well as much infested soil as possible).
Solarisation
Fungus and other pathogens in the top layers of soil can be destroyed by covering the soil with thin, clear or black plastic film and leaving in place for a number of weeks in the summer/hottest months before planting crops. Try to use recycled plastic to avoid the extra pollution of plastic production.
Virus
Plants cannot be cured of viral infections, so prevention is required.
Hygiene
Cleaning of tools (especially cutting tools) with bleach or alcohol between uses and between plants will help prevent transmission of virus.
Some pest insects e.g. aphids can transmit viruses , so control of these pests can reduce the chance of viral infection of plants.
Removal and Destruction of Infected Plants
Place infected plants in plastic bags, seal firmly and dispose of in rubbish bins or burn them.
Crop Rotation
Since viruses can only grow in living organisms for which they are specific, transmission to subsequent plantings can be minimised by practising crop rotation.
Use Virus-Resistant Varieties
Weeds
There are many options available to reduce weed infestations in your garden apart from using manufactured chemicals that have various risks associated with them. Here are a number of better choices.
Heat
Solarisation
Cover soil/garden bed with black or clear plastic film. Leave plastic in place for several weeks during the hottest time of the year. This effectively ‘cooks’ the plants and seeds in the soil underneath. This can also reduce soil-borne pathogens. Try to use recycled plastic to avoid the extra pollution of plastic production.
Steam
Apply water heated to close to boiling point or beyond boiling in some commercially available saturated steam weeding devices to create steam. When applied to a plant it causes the plant cells to rupture then wilt and die. This treatment needs to be repeated on weed infestations in order to be effective. Note that heating water to produce steam also requires use of carbon-polluting electricity unless derived from renewable sources.
Hot Water
Apply boiling/close to boiling point water to a plant. This method causes plant cell rupture, followed by plant death. This treatment needs to be repeated on weed infestations in order to be effective. Note that boiling water requires use of carbon-polluting electricity unless derived from renewable sources.
Direct Flame
Apply a direct flame using a fuel powered flame burner to a plant. The flame passes over the plant, increasing the temperature of the moisture in the plant causing cell rupture, followed by plant death. This treatment needs to be repeated on weed infestations in order to be effective. Note that this uses carbon-polluting fuel.
Heavy Mulching
Cover with overlapping layers of thick cardboard, ensuring no light can penetrate to the soil. Then covered with a thick layer of organic mulch e.g. wood chips or bark.
Prevention
Know Your Weeds
Identify the problem plant in order to ensure the treatment is targeted and effective.
Limit Soil Cultivation
Use no-dig gardening methods.
Competition
Reduce the chance of weeds succeeding by using vigorously growing plants and plant close together to restrict light to soil and, therefore, chances of germination. These plants can out-compete the weeds.
Mulch
Suppresses weeds by preventing light from reaching seeds. This prevents germination of seeds or causes the seed to use up reserves trying to reach surface. Organic and granular mulch has additional benefits of reducing evaporation from soil and capture of rainfall.
Hygiene
Control existing weeds around the garden regularly to reduce weed seed build up. Prevent weeds from being imported to your site/garden by choosing weed free plants from the nursery. Remove any weed seeds that might germinate in the top layer of the planting media. Keep tools and equipment clean.
Care with Fertilisation
Extra fertiliser can give weeds an advantage as many can grow quickly when there is ample nutrition available. Limit fertiliser use to only when necessary. Use soil testing if possible to determine nutrient needs.
Manual
Removal by Hand
Remove individual weeds by hand pulling or using hand tools is a useful technique in small gardens or for low numbers of weeds. It is highly selective and is most effective on annual weeds and weeds which do not regrow from underground parts – care must be taken to ensure the entire plant is removed. This method is cheap, free and has little to no impact on surrounding plants and animals.
Girdling or Ringbarking
For large or woody weeds too large for hand removal, girdling (ringbarking) is a suitable option. Cut several centimetres of bark from the circumference of the entire plant. This will cause the plant to die.
Mechanical Cultivation (tillage)
Using powered devices e.g. rotary hoe or tractor. This approach can have the disadvantage of requiring use of carbon-polluting fossil fuel unless the device is driven by human strength.
Could manures, composts or mulch damage plants?
As sustainable gardeners we are probably relying quite a bit on commercially sourced compost, manures and mulch to help promote healthy plant growth. But do these products reliably do that? Over the last decade or so there have been problems worldwide with contamination with substances that harm seeds and plants that we want to grow and eat.
The problem
In the 2000s, a few reports by market and home gardeners of mysterious plant damage emerged in the UK and USA. These included poor seed germination or deformed, wilting or twisting leaves. Plants affected included roses, grapes,sunflowers, potatoes, lettuces, tomatoes, spinach, some fruit, squash, hops and legumes (beans, peas, clover, lupins, acacia). In 2009, whole crops were lost in the US and hundreds of thousands of dollars’ worth of damage was done to community gardens and organic farms.1 The damage was traced to carryover of toxic substances from straw/hay mulches, composts and manures. And, of course, if from spray drift to fields or gardens. The culprits were one or more of a group of compounds that mimic naturally occurring plant hormones, called auxins, which regulate plant growth. They were pyridine carboxylic acids (pyridines) – aminopyralid2, clopyralid3, picloram, fluroxypyr or triclopyr, the active ingredients in broadleaf herbicides which affect the division of cells causing them to became disorganized and uncontrolled, eventually destroying plant tissue.
These substances are available in agricultural products, either alone or in combination, as selective herbicides to kill broadleaf and woody weeds such as docks, thistles and nettles, blackberries, gorse, hawthorn, lantana, dock, ragwort but allow other plants to grow. They have mostly been used in pastures, but also in crops of corn, wheat, barley, oats, wheat, triticale, canola, fallow land, in forests on golf courses, parks and on grass along highways. Since pyridines are growth inhibitors, they are only effective if sprayed on actively growing plants. Problems observed in plants grown by market and home gardeners were a result of carryover of these substances from composts, manure and mulch derived from sprayed land.
In Australia a number of years back, there have been reports of problems in home gardens. Agricultural products currently containing these pyridines include Tordon, Grazon, Stinger, Tri-Pick, ForageMax, Hotshot, Starane, Spearhead and Vigilant4.
How do these substances get into edible plants?
Under the right conditions pyridines persist in sprayed pasture and crops and in soil for a long time. The half life (i.e. time taken for half the amount to be broken down) of aminopyralid 32 - 533 days, very commonly around 103 days and it is stable in water (see Chemwatch aminopyralid.pdf). Breakdown is largely by microbial action. Clopyralid’s half life in soil is 1 – 2 months but can extend to 1 year depending on conditions3. Picloram has a half life of about 2 months in heavy clay soil but if organic material is present in the soil, its half life can be much longer. Again, breakdown is by soil microorganisms and occurs slowly. These substances are quickly taken up by plants via their roots, a little via their leaves and they easily translocate through the rest of the plant. The other two compounds, trichlopyr and fluoroxypyr have half lives of around 40 days in soil and around 1 day in water.
These substances are resistant to digestion by animals grazing on sprayed pastures so can be found in manures – and in concentrations high enough to damage plants that are sensitive to them. They are also resistant to the high temperatures of commercial composting. And susceptible plants need only minute concentrations to be affected.
Once the problem was recognized, Dow AgroSciences, the main manufacturer, suspended production of the offending products for a while. Now, however, the substances are still in use but with labelling and warnings in information accompanying the products.
Warnings to Prevent Problems
Statements, which vary with the product, include “do not plant crops for up to 9 months after spraying”, “Do not send treated crops off-farm as fodder or forage.” For example, the statement on ForageMax (aminopyralid) is:
“MANAGEMENT OF RESIDUES IN COMPOST MULCHES AND ANIMAL WASTE
Do not send treated crops of farm as fodder or forage. Aminopyralid residues from treated plants may pass into animal manure. If the manure is used to make compost or spread around plants it may cause injury to sensitive plants. Do not spread manure from animals that have grazed or consumed forage or fodder from treated areas on land used for growing susceptible broadleaf crops.
Dairy and feed pad effluent
Effluent from animals grazing forage brassicas treated with ForageMax within the last 4 weeks may contain residues. Effluent from these animals may contain residues for 3 days after removal of the animals from the ForageMax treated crops. Disposal of this effluent by irrigation may cause damage to clover and other sensitive crops during this 3 day period. Do not send any effluent (or compost made from it) off-farm, from animals that have grazed on crops treated with ForageMax within the last 4 weeks, until the animals have grazed for 4 days on clean feed. This restriction is not required if 4 weeks has elapsed from treatment to grazing or the animals have been on clean feed for at least 3 days.5
Can warnings on product labels and instructions for use prevent problems?
Ideally “yes” - if users read and obey them. However, some products have brief and confusing statements – one saying that there is no withholding period for grazing, another (Tri-Pick) “check the label for the withholding period for these crops” and another states “at least 7 days”.
As the United States Composting Council wrote in 2013 (current publication date is May 2016)1 "Instructions on labels often appear complicated, they may not be read completely, or if they are, are not fully understood or not followed accurately. Though some applicators might follow instructions correctly, there are usually others downstream who receive treated residues and may be unaware of the initial labeling requirements. Others may be aware of labeling requirements but choose to ignore them"
As a result, they call for more action: "The US EPA (Environment Protection Authority) should revoke the registration of all herbicides known to persist in compost at levels that are toxic to plants and require that these products be removed from the market." Currently, the US EPA indicates that a review started in 20146 but, as far as we are able to determine, no result has yet been forthcoming.
Pyridines in Herbicides for Garden Use
Unfortunately, pyridine compounds are also present in some garden products, so if you are using them (most sustainable gardeners don’t) watch out!
They are mostly called “blackberry and tree killer” or “blackberry killer”. Picloram and triclopyr (the less problematic chemical) are in Superway Tri-Pick. A number of other products contain triclopyr. Warnings about their use vary and include “The estimated half-life in above ground drying foliage as in a forest overstory is 2 to 3 months”, “Insufficient data to be sure of”, “Do not allow spray to get on to plants wanted”. One Tree Blackberry Killer warns not to let spray touch non-target plants.
Should we be cautious?
The warnings on agricultural products are certainly reducing the frequency of pyridine carryover in compost, mulch and manures and, therefore, subsequent plant damage. However, these compounds are not routinely tested for in such products and we don't have information on whether they are still likely to be present. But it would be wise when buying these products, to do one or more of the following:
- For mulches and composts, ask your supplier about the source, what sprays had been used, withholding periods etc
- For manures ask what food the animals had eaten. If grazed on pasture, ask about sprays and withholding periods. Bear in mind the a lot of cow manure comes from feed lots and it is not easy to know what the cattle had been fed.
- Use only lucerne or pea straw as mulch since the growers of such legume crops would not use pyridine herbicides because they would kill their crop
- Buy only organic-certified products
- Make your own compost and mulch
- Get your own chickens to provide manure, but check what you feed them
- Avoid blackberry and tree killers containing pyridines.
References
1. http://compostingcouncil.org/wp/wp-content/uploads/2016/05/USCC-Position-Statement-on-Persistent-Herbicides-FINAL.pdf.
2. www.beyondpesticides.org/assets/media/documents/infoservices/pesticidesandyou/documents/aminopyralid.pdf.
3. www.invasive.org/gist/products/handbook/11.Clopyralid.pdf.
4. www.croplife.org.au/resistance-strategy/herbicide-mode-of-action-groups.
5. http://msdssearch.dow.com/PublishedLiteratureDAS/dh_0940/0901b80380940cc9.pdf?filepath=au/pdfs/noreg/012-10959.pdf&fromPage=GetDoc.
6. www.epa.gov/pesticide-reevaluation/groups-pesticides-registration-review.
Why Sustainable Gardening?
Some people might ask why SGA talks about sustainable gardening rather than just gardening.
The fact is that horticulture in the hands of home gardeners, gardening professionals, nurseries and garden retail centres can have wide reaching deleterious impacts on the natural environment far from urban gardens. SGA's goal is to help you prevent these impacts and, at the same time, make your gardens joyous, healthy and productive places.
Here are some things sustainable gardening can do.Read more
Chemical Terms
Use this guide to help you make the most sustainable decision possible when, if there is no alternative, you need to use chemicals.
Active Ingredient: The portion of the chemical formulation directly responsible for herbicidal/pesticidal effects.
Biological Control: Using biological methods to control pests, eg. using the bacteria Bacillus thuringiensis to control caterpillars.
Broadcast Application: An application of spray over an entire area rather than only on individual plants.
Broadleaf Weeds: Plants with broad leaves, including flowers, trees, and many common weeds of lawns.
Certified Organic: Denotes products that have met strict guidelines set up by government approved certifying associations when grown, processed and handled.
Contact Herbicide: Only affects the part(s) of the plant(s) that the herbicide is applied to. When contact herbicides are applied to established perennial weeds, the above ground sprayed portion of the weed is usually destroyed, but regrowth can occur from the underground parts of the plant (The roots, rhizomes or tubers).
Dormant Spray: A spray that is applied after a deciduous plant has entered a stage of dormancy - that is, dropped its leaves (generally this occurs in winter).
Drift: Spray particles that are carried away from the target plant by the wind.
Foliar Treatment: Applying pesticides to the leaves (foliage) of the plant.
Integrated Pest Management: Using a combination of biological, chemical and/or mechanical means to control a pest.
Knockdown herbicides: May be either contact or translocated and can are used for the control of emergent and/or established weeds.
Leaching: The downward movement of the pesticide/herbicide into the soil, usually associated with water movement.
MSDS: Material Safety Data Sheet.
Mode of Action: The chemical reaction that takes place when a plant is treated and controlled by an herbicide.
Non-Selective Herbicide: Doesn't discriminate between target and non-target pests.
Noxious Weed: A plant that is required by state law to be controlled and eradicated.
Organic: Technically, any compound containing carbon, which is present in anything that has ever lived! When choosing organic products search for certified organic products to be on the safe side!
Pesticide: Substances intended to repel, kill, or control any species designated a "pest". This includes weeds, insects, rodents, fungi, bacteria and other organisms. This family of pesticides includes herbicides, insecticides, rodenticides, fungicides, and bactericides.
Post-Emergent Herbicide: A herbicide used to control plants after the plant emerges from the soil.
Pre-Emergent Herbicide: A herbicide used to control plants before the plant emerges from the soil.
Residual Herbicide: A herbicide placed on the target area that remains active in the soil for a period of time.
Selective Herbicide: Controls only certain types of plants without affecting other types of plants. Some of these act by interfering with the growth of the weed and they are often based on plant hormones.
Surfactant: Surface-active agents, emulsifiers, detergents, spreaders and dispersing agents capable of improving the effectiveness of the herbicide.
Systemic: A chemical which is absorbed directly into a plants vascular system. This method is used either to kill pests feeding on the plant or to kill the plant itself.