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 sourcesSGA 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

  1. 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)
  2. 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.
  3. Independence and objectivity – No preference to any products or for any manufacturer is given.
  4. 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.
  5. 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.
  6. 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.
  7. 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
  8. 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.

Go to WiseGardening ratings

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):

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.

Go to WiseGardening ratings

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.

[wpdatatable id=5]


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!

Go to WiseGardening ratings

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

Diseases

Weeds

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.

Go to WiseGardening ratings

Low Impact Pest Management 101 Video

Sustainable Gardening 101 Video Series

PART 3: Low Impact Pest Management

Gardens are the natural habitat for all types of insects – the good, the bad and the ugly. Learn how to avoid unnecessary chemical use by managing the pests in your garden by using nature and its resources to strengthen the balance towards the beneficial kind.

Topics Covered

  • Being a detective – identifying the culprits
  • Beneficial insects vs pests
  • Using barriers and cultural strategies

Information about risks and safety of commercial chemical pesticides is in SGA’s app WiseGardening – Choices to Protect You and the Planet.  Safety of home-made pesticides could not be included in that app due to unavailability of information about their soap, detergent and oil ingredients.  Always use them with caution.


Early Blight of Tomatoes

Hi, my name is: Early Blight of Tomatoes

Describe yourself: I'm a saucy little fungal disease with a real thing for the leaves of tomato plants! People say I'm common, but I reckon I'm an angel, a brown spot with a gorgeous yellow halo.

Hobbies: I adore the older leaves of tomato plants, but don't mind a stem, or entering the fruit through growth cracks or the fruit stalk. I'm movin' on up baby... I start on your older leaves and work my way to the top of the plant, causing defoliation as I go. If I have to have a young plant, I would definitely go for the base of the stem... I'm partial to a bit of collar rot!

Likes: Oh, I love to get busy when the weather is over 15⁰C and there is lots of moisture around... it really gets my spores flying and my lesions growing! Love humidity, when you over fertilise your tomatoes (oh yeah baby, I love that), shade and water lying around on leaves. I love really crowded gardens where there is no air movement.

Dislikes: Sun, well mulched garden beds, when you clean up fallen leaves, hate well prepared soil with heaps of organic matter, home made spray remedies (like milk sprays and bi-carb mixes), store bought good sprays. I really don't like gardeners who monitor their plants all year round!

You'll know you've met me when: Your tomatoes lack serious vigour, older leaves are seriously ugly with spots, and some fruit shows damage (at the stalk end). Check young plants for collar rot.

Breaking up ain't hard to do... if you

  • Mix fat-free milk with water in a 1:1 ratio and apply it using a spray bottle. Spray the solution directly onto the clean leaves of your tomatoes. Milk-and-water solution coats the leaves and leads to the growth of an invisible fungus that frightens off black spot!
  • To four litres of water, add 3 level teaspoons of bicarbonate of soda and a couple of good splashes of fish emulsion. Give it a good mix and spray it on weekly. Don't apply when it's hot. The Fish emulsion is very useful because it helps to make it stick. It also contains beneficial bacteria that have antifungal properties. And that's not all - the oils in fish emulsion will help to suffocate pests like mites/aphids/scale. You must use it weekly for it to be most effective.
  • Seaweed sprayed onto the leaves changes the pH of the leaf surface making it less attractive to the fungal spores. It also strengthens the cell walls making it more difficult for the invading fungi.
  • Low Environmental Impact fungicides are available, but success is limited and control can be difficult.
  • Destroy all infected plants and dropped leaves by bagging and disposing in rubbish, or burning. Do not compost.
  • Rotate your crops!!! Don't plant the same crops, or susceptible crops in the same area each season.

Photographs:

Banner Image:  Dwight Sipler from Stow, MA, USA - Early blight on tomato leavesUploaded by Jacopo Werther, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=25221133

Pic 1: www.avrdc.org Des: Fruit symptoms of Early Blight of Tomato
Pic 2: www.plantpath.iastate.edu Des: Foliage symptoms of Early Blight of Tomato
Pic 3: www.apsnet.org Des: Stem lesion caused by Early Blight of Tomato


Staying Safe While Gardening

Gloves, socks and sometimes masks are very important in preventing disease obtained by gardening -  the last thing you want, especially with the coronavirus around.  Since, currently, people are becoming more interested in gardening – both to grow food and to do general tidying up and planting because of increased time at home while social distancing, we really need to be protecting ourselves by wearing the right clothes!
Read more


Sooty Mould

Hi, my name is: Sooty Mould

Describe yourself: I’m definitely one of the most appropriately named pests and diseases going around...I look exactly like black soot or charcoal. Technically, I’m a fungus that feeds on the sweet honeydew left by some sort of sap-sucker (like aphids, scale or mealy bugs), and will follow an infestation of this kind.

Hobbies: I LOVE making your precious plants really unsightly, covering leaves and even stems in a grey to black soot. I don’t actually harm your plants, and in fact I’m a pretty good indicator that there is some other sort of pest issue that needs to be controlled.

Likes: Just about any sort of plant is appealing, but remember, I can’t exist without the delicious exudates of a sap-sucking critters.

Dislikes: Gardeners who keep pest problems under control and practice good garden hygiene.

You’ll know you’ve met me when: The foliage of your plants looks as though it has been dusted with charcoal. Sooty mould can feel sticky to touch, and will wipe off fairly easily.

Breaking up ain’t hard to do…..if you:

• Remove or treat the honeydew producing insects and the sooty mould will disappear.
• Sooty mould can be removed by wiping the affected foliage with a damp cloth. This is only temporary and re-infestation will occur if the other pest issues are not treated.
• Collect fallen leaves affected by sooty mould and place in bin – DO NOT compost!
• Controlling ant populations, who tend the honeydew producing insect, will minimise the opportunity for them and the sooty mould to take residence on your plants. Repel ants by planting ant-repellent plants such as tansy nearby. Check the base of the plants for large ants’ nests; and, if found, mulch with tansy, and increase regular watering to discourage ants and sooty mould.

Banner photo:  from image by Erika Magarifuji in Scot Nelson album.


Cucumbers

Cucumis sativus 

Fresh, pickled or as an ingredient in many a dish and used the world over, cucumbers have a lovely place in the summer garden. Although they need a fair amount of love and tenderness they reward the grower with beautiful fruit. Home grown cucumbers are usually a bit knobbly and may not be as perfect as the shop bought, but they make up for that in their taste and texture.

 

Planting Schedule

Warm Areas: July to March
Temperate Areas: September to January
Cool to Cold Areas: October to December

Location
Cucumber’s can be a bit fussy about position. In cool zones, they love nothing more than a spot in full sun. However, in areas with hot summers, a little tenderness and shade will encourage your cucumbers. You can actually grow cucumbers in about 30% – 50 % shade in places where the air is warm. A simple shade covering, temporary or something more permanent will protect the plants from the harsh sun as well as reducing the risk of scarring the fruit, (it might have the added benefit of protecting your plants from pests too).

Another thing to consider with cucumbers is that they are essentially vines and they need to climb. Pick a position that provides them with the right amount of sun and also gives them a bit of support. Fences and trellis do fine as do wire supports. Alternatively you can use sweet corn as a “living stake” for cucumbers. It makes the most of the space in your patch and is a sustainable solution for staking. This works best where there is good airflow ; and these two are excellent companions.

Soil
Good soil preparation is vitally important. Cucumbers need a friable (loose), well drained soil, full of organic matter, especially compost. Plant in a mound about 40cm across, with two cucumbers to each mound. This acts to improve drainage.  Add a good straw mulch to help keep the roots cool, stop the soil drying out and prevent the fruit come into contact with the ground,  helping to prevent fungal diseases, (more on that later).

Feeding
Being a fruiting plant, cucumbers require a reasonably high level of feeding, especially when it comes to fruiting. This means that they will pretty much take in whatever food is available and this is where you need to be a bit careful. A good amount of compost is the best starting point. Anything stronger than this can encourage a lot of healthy leaf growth but does not encourage fruiting.   Give cucumbers a feed at planting time with either watered down worm wee or a seaweed based liquid feed. Feed again when you see the first little fruits appear (they look like tiny gherkin).

What about the Water?
Cucumbers present a convincing argument for drip-irrigation and rainwater tanks - they are thirsty!   Installing drip irrigation in your produce patch should always be considered, but it’s almost a necessity with cucumbers. Drippers on top of the soil, under a nice 5cm – 7cm layer of mulch and directed around the base of your plants is perfect. Its puts the water exactly where it’s needed… the roots!

Cucumbers don’t respond well to other methods of watering as they are susceptible to fungal diseases if their foliage is wet.   Don’t let them dry out either or you may end up with bitter or dry fruit.  If you must hand water cucumbers, make sure you do it first thing in the morning ensuring that you are aiming mainly at the root zone of the plant avoiding the foliage.

Harvesting
The variety  of cucumber you chose will determine when it’s ready to pick and a number  of varieties that have multiple uses.  If you want gherkins, pick the long, green cucumbers when they are about 5cm – 10cm in length. Alternatively, these can be left on the plant and picked when they are 15cm – 20cm for tasty “salad” cucumbers. Same deal for Lebanese cucumbers. The round apple shaped cucumbers are best picked when they are about tennis ball size. Cucumbers generally take about 8 – 10 weeks to ripen, stretching out to 12 – 14 weeks for apple cucumbers. Make sure you monitor your vines regularly; it’s better to harvest when cucumbers are under-ripe, rather than over-ripe.

When harvesting it's best not to pull the fruit off the vine.  Pulling them off can snap the vine in half and seriously jeopardise the rest of your crop. Cut the cucumbers off with a sharp pair of clean scissors or secateurs, making sure you leave a bit of stem attached to the fruit.

Pests and the Rest
Cucumbers, like many vines, are susceptible to fungal infections. Prevention is much better than a cure so; clean straw mulch, drip irrigation, good air movement, a trellis or support and root level or early morning watering should deter fungal spores.

Another issues faced by the cucumber is lack of bee activity to pollinate the flowers. Encourage bees into your patch by planting a diverse selection of flowering companion plants, edible and non-edible.   This will hopefully reduce the use of unnecessary pesticides in the garden that often wipe out the good guys as well as the bad.  You can hand pollinate your cucumbers if you are concerned;  simply pick a male flower (one without a small fruit forming at the base) and touch it lightly onto the centre stem of the female flower.

 

Final Tip
Give your cucumbers a little pinch!  “Pinching out” is a term that just means removing wee bits of the plants to encourage better growth and fruiting. Pinch out growing tips when they have formed about five to seven leaves; also pinch out the laterals (side shoots) that have produced a number of leaves (about eight to ten) but no female flowers ( the ones with the miniature cucumber where the petals start).

Photos
Photos taken by Elaine Shaulle (SGA) and Mary Trigger (SGA)
 


Pea Blight

Bacterial disease such as pea blight can be tricky to diagnose since bacteria aren't visible to the human eye; in fact they can only be seen under high magnification (x 1,000).

Pea blight is caused by Pseudomonas syringae pv. pisi and/or P. syringae pv. syringae.  Laboratory tests will reveal the presence of bacteria, but as these tests can be costly, it's not really a consideration for the home gardener.

Disease symptoms on plants can be confused with fungal diseases, environmental extremes, chemical toxicities and even senescence.

Take heart though, blight of peas can be more of a problem in large scale horticulture than in the home garden. But in the home garden it could affect all the peas in a small space and wipe the whole lot out.  However, in the home garden it is easily controlled by keeping your soil healthy with organic matter and manures, and rotating crops.

Symptoms

Small, dark-green marks that look soaked with water appear on the leaflets (as shown here). These lesions enlarge and merge together (coalesce), but are limited in their expansion by the leaf's veins.

The lesions on leaves turn yellowish and are later brown and distinctly papery. Lesions on pods (shown below) are sunken and turn an olive-brown. Lesions can also develop on stems near ground level, beginning as 'water-soaked' areas. When these lesions coalesce they cause the stem to shrivel and die.

Stem infection may spread upwards into the leaves and stipules.

Infected seedlings are killed very readily, but even advanced plants can be killed by the disease.

Heavily infected seed may be discoloured. However, there is no visible effect on seed with light infection.

Spread

Spread of the bacteria is by seed or survival in pea trash. Rain-splash and wind-borne water droplets can also spread the bacteria.

Excessive rainfall and strong winds are the most favourable environmental conditions. And plants damaged by frosts and heavy rain are most susceptible to attack.

Prevention

Blight is most severe in wet seasons, so be vigilant when conditions are most favourable to the disease.

Purchase clean seed and, of course, do not use seed from plants that have any disease symptoms.

Seed treatments are not effective for the control of bacterial blight.

Do not grow peas in the same place each year, or even adjacent to an area of pea stubble. In fact, peas should not be grown in the same place more than once in three years.

Early sown crops are more vulnerable than late sown crops. Never sow earlier than recommended for your district.

Control

Bacteria will survive on pea stubble, so if infection is suspected, bury the pea trash 10cm below the soil surface, which reduces the survival time of the bacteria significantly.

Better still, remove all infected plant parts, bag and put in the rubbish bin.

Peas should then only be grown on a rotation of one in four years.

There are copper-based compounds available for the control of this disease in field peas but their effectiveness is 'limited and inconclusive' (DPI Victoria). Fungicides are for fungal diseases, they do not work on bacteria.

Information sources:

Kerruish, R.M., & Unger, P.W., 2003, Plant Protection 1, 3rd Edition, published by RootRot Press ACT.
Richardson, H. & Hollaway, G., 2007, 'Bacterial Blight of Field Peas', Agricultural Notes, July, AG0148, State of Victoria, Department of Primary Industries.


Bacteria


More than 200 different plant bacteria cause plant disease in Australia. However, there's also a host of bacteria that are beneficial to the plants we grow. Some bacteria have been harnessed for commercial products, to control plant pests and diseases, and some live in mutually beneficial, symbiotic relationship with plants.

Beneficial Bacteria

There is a long list of bacteria that help our gardens stay fertile and help break down and recycle nutrients.  Here are just a few.

Agrobacterium sp

Scientists had been battling the 'Baddie' Agrobacterium that causes Crown Gall Disease for decades. It causes cancer-like growths on lower stems and roots. It was a particularly devastating disease of the fruit industry worldwide.

In 1969, a student at the Waite Agricultural Research Institute in Adelaide isolated a strain of the Agrobacterium that infected plants but didn't cause the cancer-like growth. In fact, this benign strain somehow protected young fruit trees against the virulent form of the same bacterium.

Professor Allen Kerr and his team dubbed the strain K84 and later discovered why it worked. K84 produces an antibiotic that is deadly to the pathogenic strain but it is unaffected itself because it possesses a resistance gene that makes it immune to its own antibiotic (and this antibiotic was also found to be harmless to most other bacteria).

Unfortunately, the close relationship also meant that eventually there was gene swapping and the pathogenic strain also developed resistance. Undeterred, the team then worked with overseas scientists, and identified the region of DNA that allowed the transfer to other bacteria. They deleted this region. The bacterium retained its ability to synthesise the antibiotic, but could not pass the resistance gene to other bacteria.

This genetically modified bacterium was then called K1026. In 1988, the NSW Department of Agriculture approved K1026 for commercial use as a pesticide. It was subsequently given the name No Gall and this product is now used all over Australia. It's not been approved for release overseas, as K84 is still an effective control.

In 1990 Professor Allen Kerr, Professor Eugene Nestor (USA), and Professor Jeff Schell (Germany) were awarded the Prime Minister's Australia Prize for Science for this work.

Bacillus thuringiensis (Bt)

Various forms of this bacterium have been harnessed to control some species of leaf-eating caterpillars (like the Cabbage White caterpillar pictured right), mosquitoes and varieties of beetles. It can be found in products called Dipel, Xen Tari, Cybate, Vectobac, and Novodor.

Bt is a naturally occurring soil bacterium and several strains are known to kill insects. Bt's ability was discovered in 1911, but it wasn't commercially available until the 1950s.

Unlike typical nerve-poison insecticides, Bt acts by producing proteins that react with the gut lining. The proteins paralyse the digestive system and the insect stops feeding. The Bt-affected insects die from starvation, which can take several days.

Rhizobia

Nitrogen-fixing bacteria. Legumes (members of the Fabaceae family, which include peas and beans) have a symbiotic relationship with this bacterium. The bacteria are seen as nodules on the roots of legume plants, as can be seen above, and should not be confused with nematode damage (see our information sheet on Nematodes).

Rhizobia provide the plant with additional nitrogen that would otherwise be unavailable to it by converting nitrogen from the atmosphere into ammonia that plants can use.

Legume crops therefore require less nitrogen than other crops because of this relationship.

Acacias have the same relationship with bacteria, and because they are one of the first plants to germinate and grow after fire, they help the plants that follow. Acacias provide nearby plants with nitrogen all year round.

When using pea straw as mulch, often pea plants will germinate. This is to be encouraged. Chop the plants down before they flower, and you also have additional nutritious mulch. Win, win!

Composting Bacteria

Very important for recycling nutrients are the bacteria which are active in both soil and compost heaps.  Most of the composting work is done by bacteria, but fungi and yeasts, as well as certain bugs assist. And, of course, worms very valuable too.

There are a large number of different bacterial species but they can be broadly divided into aerobic (requiring oxygen) and anaerobic (do not require oxygen).  Aerobes are most efficient at breaking down organic material and do most of the work to release the nutrients (carbon, nitrogen, phosphorus and minerals) that provide the growth-promoting qualities of compost.  To keep them happy we need to turn compost heaps regularly, avoid them getting "gluggy" or put in tubes with holes punched in them to keep an air supply going.

The anaerobes can also break down organic material, but rather slowly and, if there are too many of them, compost piles will start to smell ugly because they release hydrogen sulphide which smells like rotten eggs.

Biodegradation - various species

Various bacteria species have been found to break down pesticides, pollutants (such as hydrocarbons in oil spills, as seen above), sulphur and nutrient residues into non-toxic compounds.

They are being used in bioremediation and as natural biodegradation agents.

Other

Plant growth promoting bacteria (PGPR) are various species of bacteria that exist in the root zones and enhance plant growth.

Ice nucleation active (INA) bacteria, such as Erwinia herbicola, are epiphytes, that is, they are grown upon or attached to plants. These bacteria actually promote frost damage to sensitive plants by initiating the formation of ice crystals.

So foster growth of beneficial bacteria in your garden.


Gall (of Australian Native Trees)


Hi, my name is: Gall (of Australian Native Trees)
Describe yourself: I guess some people would describe me as an abnormal growth on plant parts, but I reckon I'm just a regular lump, hanging around on stems, leaves, buds, and, when the mood strikes….roots! I may look pretty boring (and a little ugly) on the outside, but I'm actually really interesting under the surface! Size wise, I can go from minute to big and hideous, and my colours can vary from red to yellow and even brown!

Hobbies: I am the result of plant cells' reaction to invasion by my friends e.g. wasps, beetles, moths, coccids, psyllids or bacteria. I don't move around at all (I just hang out growing bigger and bigger) and, once I've settled in, I stay for a long while!

Likes: Loads of Australian native plants, but I really love Eucalypts, Acacias, Lilypillies and Hakeas. I like making your prized native trees look really ugly... but I don't always kill them!

Dislikes: Well... not much, but the little pests who cause me are not huge fans of birds and other insect eaters. You see, I am often formed when little wasps, beetles and insects lay their eggs in plant parts, so a really diverse habitat with loads of bird activity will certainly upset me!

You'll Know You've Met Me When: Certain parts of your trees have lumps on them. In wattle trees and hakeas, I grow on the branches and look like a big seed pod. But on eucalypts I can appear a bit like a little pimple on the leaves. When I hang out on lilly pillies, I look like bubbles and pimples on their beautiful foliage!

Breaking up ain't hard to do... if:

  • Accept that tiny lumps and bumps are all part of nature….I mean, we can't all look like supermodels!
  • Encourage backyard biodiversity….having birds, lizard and insects in the garden will help keep the critters that cause galls under control.
  • When buying Lillypillies, look for varieties that are less susceptible to psyllid….there's heaps of them out there!
  • Cut off areas if they are really offensive to you….as I said, I probably won't kill your tree, so this is a last resort!

Photographs:

Pics 1&2: Coccid Gall on Eucalypt
Pic 3: Fungus Gall on Acacia sp.
Pic 4: Wasp Gall on Acacia sp.


Winter Washing of Fruit Trees

Although it may look like there is not much happening with your fruit trees over winter, the microscopic world of fungi is making plans, strategically laying in wait in the cracks and crevices of your trees until the weather warms up. The most prevalent fungus is Peach Leaf Curl, causing the disfigurement of leaves, and sometimes the fruit, on your peach, nectarine, apricots and even almonds. However there are many other fungal problems that may occur and winter spraying is a good way to help reduce the incidence of fungal problems.

Peach Leaf Curl will cause the lovely new growth on your trees to appear blistered and puckered and in severe cases it can cause pimples on fruit and premature fruit drop. In the cool moist weather of early spring the fungus will multiply and if the cycle is not broken your trees will continue to be infested year after year.

Other fungal diseases that may be dormant on stone fruit include Shot Hole, Freckle Spot, Rust and Powdery Mildew.

There are several things you can do to minimise the spread of Peach Leaf Curl and other fungal diseases in the garden.

Practise good garden hygiene. Pick up fallen leaves from the ground and avoid putting them in your compost. Remove damaged or rotten fruit and keep the tree pruned to an open vase shape to increase air circulation.

Plant your tree into well prepared soil in the right position with plenty of sun and good air circulation. Keep up a regular fertilising and watering schedule.

Spray your trees during winter with a low impact fungicide. ‘Winter-washing’ helps to kill off any spores and can greatly reduce the incidence of Peach Leaf Curl and other fungal problems.

Winter Washing

The best spray to use is either copper oxychloride or lime sulphur sprayed in alternate years. The first spray should be in late autumn at leaf fall just before the tree enters its dormancy. Spray again at bud swell or bud burst in late winter or early spring. Once the leaves have opened out it is too late to spray for Peach Leaf Curl and many other fungal diseases. Safe and effective spraying can only be done at the end of the following summer.

When spraying fruit trees, be aware of the potential impact that ‘spray drift’ may have on surrounding vegetation, soil micro-organisms, pets and humans. Spraying is usually done to the point of ‘run-off’, where the spray liquid has completely covered the tree surface and runs off on to the ground. It may be prudent to lay spray sheets down so non-targeted areas are being protected.

Only make up enough spray for the job at hand to avoid the problem of having to dispose of excessive amounts of unused spray.

Spraying may not be 100% effective so be vigilant over summer and remove any leaves showing signs of fungal disease as soon as they appear.


Virus or Variegation

A common error gardeners make is to assume that appearance of coloured areas on leaves is caused by natural variegation, fungal infection or nutrient deficiency.  In many cases, the variegated colour of leaves of some shrubs, indoor plants, lettuces, herbs is a natural mutation.  Happily, this is not a destructive mutation, but one that results in less chlorophyll in some parts of the leaves, causing a paler and mottled effect.  Sometimes, keen gardeners have selected these plants and bred from them. These variegated plants can be lower in vigour and shorter-lived than their 'normal' relatives but this hasn't affected their popularity as garden plants.

Variegation Due to Plant Viruses

There is, however, variegation caused by some sort of plant problem. Although some garden pests, such as aphids can cause leaf yellowing, this colour change is not the only sign of an infestation.  A more problematic cause of colour change is infection by disease-causing viruses or virus-like viroids and phytoplasmas, of which there are hundreds.  Shown at the left is the leaf symptoms of cucumber mosaic virus (image courtesy of www.whitefly.org).

Fortunately, trees and Australian native plants have few virus disease problems and, interestingly, viruses in wild-growing plants don’t seem to develop disease, although they have not been studied as well as cultivated plants.  It is in cultivated plants, mainly food crops, that virus infection is of most concern. Because viruses and virioids are very simple “organisms” with DNA or RNA coated by a protein layer. They cannot survive for long or multiply outside of a host so they are 'obligate parasites' - they can only increase in number inside a living organism.  Once inside the plant, the plant is harnessed into producing more virus.  The plant cannot grow properly because its energy and nutrients are diverted away from normal activities like photosynthesis.

Shown here are the leaf and fruit symptoms of tomato spotted wilt virus (images courtesy of North Carolina Co-operative Extension).

Virus infection may result in a variety of symptoms - leaf colour variegation (which may be mottling, stripes or sport) is just one.  Viruses may infect all parts of the plant but symptoms are generally most obvious on young foliage.  Some result in ringspots, such as ringspot virus on Cymbidium orchids; bronzing, such as that caused by tomato spotted wilt virus; malformations, as caused by potato leafroll virus; and wilting, also caused by tomato spotted wilt virus.

Classification

It is common practice to use the common name of a virus, rather than its scientific name (unlike the use of botanic names of plants).  Viruses are named based on the first plant on which it is studied, followed by the most obvious symptom of the disease on that plant, followed by the virus group to which it belongs.  For example, apple mosaic virus is the common name of the apple mosaic ilarvirus, and tulip breaking virus is the common name of the tulip breaking potyvirus.  Many viruses have a wide host range, not just the plant it is first studied on, and the symptoms can vary.

Spread

Seed

Plant viruses, like those infecting humans and other animals are spread by some sort of contact. More than 20% of virus diseases are spread via seed where the virus is mostly in the cells required for growth, but some are in the seed coat.

Vectors/Carriers

Some are spread by vectors such as aphids and thrips.  Shown here is rose mosaic virus.  This is likely to be spread by aphids (image courtesy of The Utah Department of Agriculture and Food, Division of Plant Industry).  Some are carried by single celled organisms such as Polymyxa betae which transmits Beet necrotic yellow vein virus by infecting plant roots.

Sap

If plant leaves become damaged by cultivation or animals feeding, sap containing virus may be transmitted another plant.  This has been observed with cucumber mosaic virus.

Other

Although rare, nematodes and fungi are also implicated.  Parasitic plants can spread viruses. Tobacco mosaic virus can even survive in dead infected tobacco leaves in cigarettes.

All virus diseases will be transferred from infected parent plants through new bulbs, corms, tubers, stolons, and cuttings.

Control

As we know from human virus epidemics, animal viruses are almost impossible to control except by avoiding exposure, mounting our own immune system to fight off the infection or by vaccination. Plant don’t have the same options - once a plant is infected it remains infected.  Some viruses do not infect the growing tip of a plant (the meristem) and this is often used to advantage by growers. The unaffected tissue from the meristem of a plant can be tissue-cultured and can result in virus-free plants.

There are no chemical or biological controls.

So prevention is the only effective control. Methods include:

  • Removing infected dying plants and destroying them so that vectors such as aphids do not spread the virus to healthy plants.
  • Keeping weeds away - they can host viruses, so keep the surrounds weed-free.
  • Paying attention to your own hygiene because some viruses can be spread by handling, so hand-washing between plants can be a necessity.
  • Sterilising pruning and cutting implements after every plant or plant group – dip or wipe tools with methylated spirits
  • Growing disease-resistant varieties - many resistant varieties of crops of economic value have been developed.
  • Insect -proofing greenhouses. Professional growers often rely on insect- proof greenhouses to keep out possible virus-carrying vectors.
  • Quarantining plants for suspect locations.

There are many virus diseases not yet in Australia, so quarantine is an important method of preventative control.  Please adhere to quarantine legislation - you never know what a plant or seed might be carrying.