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Gardening … all naturally

2016 Edition

Opt for alternatives to pesticides

How to solve the problem of undesirable organisms and diseases in your flower beds and garden

 Undesirable organisms and symptoms

Tricks and suggestions for prevention

 Alternatives to pesticides

Pesticides: a last resort1

Slugs and snails

- Eat plant leaves.

- Easier to spot at night when they are more active.

- Create a barrier around your flower beds and garden using oven-dried crushed egg shells (pluck up the slugs and snails already on the scene). - Place a receptacle (saucer) or a commercial trap containing beer or a mixture of water and yeast on the ground, making sure that the edge of the receptacle or trap is at ground level; empty and replenish as needed.
NB: Slugs are attracted by the yeast in the beer.

- In the evening lay wooden boards on the ground, and in the morning pluck up the pests hidden underneath.

- Use copper bands available in retail outlets as repellent barriers. Slugs are made up almost entirely of water and receive little electric shocks upon contact with copper.

- Ferric sodium EDTA

- Ferric phosphate

- Diatomaceous earth


- Cut plant stems.

- Easier to spot at night when they are more active.

- Plant marigolds (French marigolds) since these flowers repel cutworms.

- In fall, remove all plant debris from your flower beds and garden.

- Dig and turn over the soil in fall.

- As the plant begins to grow, place a bottomless tin can, a plastic cup or a sheet of aluminum foil around the stem, sticking up at least 5 cm above ground level and pushed in at least 3 cm beneath (do not remove for 3 weeks).

- After sunset, using a flashlight, carry out a cutworm collection.

- Rotenon
Colorado potato beetles (“potato bugs”)

- Feed on potato leaves.

NB: Not to be confused with ladybugs, which are useful.

- Plant garlic or marigolds between rows since these plants repel potato beetles. - Eliminate by hand the masses of orange eggs found under the leaves (usually in June).

- Water leaves with a powerful spray in order to dislodge the bugs.

- Pluck up larvae, as well as adult insects, in April, May and September.

- Rotenon

- Pyrethrins


- Are fond of damp, dark places.

- Generally easy to catch.

- Easier to spot at night when they are more active.

- Avoid accumulations of plant and wood debris.

- In spring, on warm dry days, work the soil; this will disturb the adults and uncover their eggs.

- Set traps: about 20 per lot, wherever you spot the pests.

- Use “tunnel” traps of all sorts, around 30 cm in length (garden hose ends, pieces of bamboo, rolled-up newspapers, etc.) or commercial traps.

- Shake out the traps in the morning above soapy water.

- Diatomaceous earth
- Insecticide soap
- Pyrethrins

- Tiny green, brown or black sucking insects, often found in groups; they cause leaf yellowing and sometimes deformation.

- May transmit viruses.

- Foster the proliferation of predators such as ladybugs and lacewings.

- Use the proper amount of fertilizer; too much nitrogen-based fertilizer promotes the growth of succulent tissue which attracts aphids.

- If possible, a powerful spray of water once a day, in order to dislodge the aphids.

- Insecticide soap

- Rotenon

- Pyrethrins

- Acetamiprid

White grubs (chafer larvae) - Turn over soil and if you uncover them continue digging deeper around the entire area; eliminate all the larvae you have uncovered by hand. - Put bait in soil (potatoes), wait a couple of days, then turn over the soil and pluck up the pests Imidacloprid
Lily leaf beetles Check lilies regularly during the beginning of the season. The larvae, which are hidden by their excrements, hide under leaves. Remove larvae and adults by hand. Be attentive. Adults sometimes drop to the ground to escape gardeners.  
Common Scab

- Brown scabs on potatoes, beets, turnips, etc. To be found in too highly alkaline soil (pH level above 7).

- Avoid excessive use of lime and wood ash. - Get a pH analysis.

- Lower the pH level, if necessary, using wettable sulphur.

– No need for treatment. An aesthetic problem only.
Mildew or late blight

- “Oily” spots on plant leaves, followed by a white covering on potatoes and tomatoes.

- Enrich soil using well decomposed organic matter.

- Choose resistant plant varieties.

- Avoid spraying leaves with cold water.

  - Copper

1 Follow the instructions provided on the label of the product.

To learn about repercussions of active ingredients for human health and environment, please see the table entitled “Relative toxicity of the main active ingredients contained in pesticides for domestic use used for green spaces" (PDF file, 134 Kb).


Solutions to the problem of undesirable organisms affecting your trees and shrubs

Undesirable organisms

Trees and shrubs affected and symptoms

Alternatives to pesticides

Pesticides: a last resort1

Aphids - Many species affected (rose trees, plum trees, honeysuckle, apple trees, conifers, etc.).

- Are also found in gardens and flower beds, as well as on house plants.

- Tiny green, brown or black sucking insects, often found in groups; they cause leaf yellowing and sometimes deformation.

- May transmit viruses.

- Rarely lead to the death of the plant.

- Trim the shrub in question before the treatment, if required.

- Water daily, if possible, using a powerful spray, in order to dislodge the aphids.

- Foster the proliferation of predators such as ladybugs and lacewings.

- Use the proper amount of fertilizer; too much fertilizer promotes the growth of succulent tissue which attracts aphids.

- Insecticide soap

- Mineral oil

- Acetamiprid

Tree-climbing insects: ants and caterpillars - A number of species affected.

- Caterpillars feed on leaves.

- Ants do not harm trees. They are attracted by, among other things, the excreted by aphids. In return, ants protect aphids from their enemies.

- Put a strip of tissue paper or cardboard (about 10 cm long and coated with a sticky substance) or sticky strips sold in retail outlets around the trunk.


Sugar maple borers - Sugar maples, as well as red and silver maples.

- Larvae that tunnel beneath the bark.

- Attack already weakened trees.

- Fertilize properly.

NB: There are few corrective measures to be taken other than to use a bendable stick or rod to kill the larvae when they are still in the tunnel. The little mounds of sawdust on the trunk point to the entry of the tunnel.

Apple maggots - Apple trees.

- Microscopic larvae that leave grooves in the apple.

- Pick up fallen fruit in order to avoid leaving infestation sites intact.

- Exercise damage control by using traps: sticky red balls in the shape of an apple or sticky yellow bars on which you place a red apple-shaped disk (5 traps per tree, hang 1.5 m above the ground; lay traps after the petals fall).

Scale insects - A number of species affected. - When there has been a proliferation, cut down the branches affected in order to reduce insect numbers. - Insecticide soap

- Pyrethrins

- Mineral oil

Bronze birch borer - Paper birch, grey birch and cutleaf weeping birch.

- Leaves dry and fall prematurely from the crown of the tree.

- Uneven ridges (called gouting) on trunk and infested branches. The larvae tunnel under the bark.

- Since they usually attack weakened trees, keep trees healthy with fertilizer and by irrigating during dry periods.

- Choose other types of trees, especially if the bronze birch borer is a problem in your area.

- Call a specialized firm.
Birch leaf miners     Generally, pesticides are needed only when a tree is subject to a severe infestation many years in a row.
Maple gall mites   The “little warts” on the leaves do not endanger the life of the tree.  
Tent caterpillars (approximately 3 cm in length)   Remove them with a stick when they gather in their nests late in the evening or during cool periods. Bacillus thuringiensis kurstaki (B.t.k.)
Leaf roller caterpillars

These caterpillars hide in rolled leaves.

The leaves are easily removed by hand. Bacillus thuringiensis kurstaki (B.t.k.)

Aphids forming witchbrooms

 Often found on honeysuckle, these small sucking insects (often pale green in colour) group together and carry a virus causing leaves to shrivel and forming witchbroom. Witchbroom can be pruned.  
Apple Scab
(caused by a fungus)
Apple trees.

Circular olive-coloured spots that turn brown and downy, found on leaves and fruit.

- Avoid vulnerable varieties (Gala, Delicious, Jerseymac, McIntosh and Cortland) and choose scab- resistant varieties (e.g.: Liberty, Jonafree, Prima, Freedom and Spartan, or crabapples such as Dolgo, Evereste, Liset and Makamik).

- Remove leaves in autumn, thus getting rid of infestation sites for fungi.

- Reduce dampness by leaving space between plants.

- Trim the tree for better aeration.

- Sulphur
Dutch elm disease (caused by a fungus carried by small insects called native elm bark beetles) - Elms.

- From mid-June to mid-July, the leaves wilt, shrivel, become dry and turn brown.

- Choose a resistant species.

- Prune well above the affected branches (2 m) and destroy them; if these branches are big or if part of the trunk has been affected, cut them down, remove the bark and burn it.

- After each time you prune, disinfect your tools with rubbing alcohol or methanol.

- Have very valuable trees treated by a company specializing in such work.
Rose tree diseases
(powdery mildew and black spot)
- Powdery mildew forms a powder on leaves; they then become twisted and turn reddish in colour.

- Black spot is characterized by the presence of round black spots on leaves, which turn yellow and fall off.

- Use resistant varieties of rose trees.

- Reduce the dampness level by spacing the plants, and avoid watering the leaves.

- Gather the dead leaves as soon as they fall in order to keep infestation sites of this fungus from forming.

- Sulphur

- Copper

Powdery mildew of lilac

Fungus on the top part of the leaves generally appears during the month of August. Gather and destroy the leaves in the fall. No treatment is needed if the infestation is minor.

Black knot found on cherry trees

  - The more quickly you remove the diseased parts destroyed by this fungus, the less damage there will be.
- Also check neighbouring wild cherry trees which could contaminate your trees.

Nectria canker (also called target canker)

Often found on the tree trunk, this fungus penetrates by way of a machine-made gash to the bark. It’s important to thoroughly protect the latter.  

Fire blight
Often found on sekuice trees (service trees) and from time to time on hawthorns, apple- trees and cotoneasters (family of Rosaceae plants).

  Ask for resistant varieties when purchasing.  

1 Follow the instructions provided on the label of the product.

To learn about repercussions of active ingredients for human health and environment, please see the table entitled “Relative toxicity of the main active ingredients contained in pesticides for domestic use used for green spaces" (PDF file, 134 Kb).


Solutions to problems of undesirable organisms affecting lawns

Harmful organisms

Symptoms or damage

Alternatives to pesticides

Insects and undesirable plants
See the section Control of the main indesirable organisms present in residential lawns (in French only)
Diseases (fungi)
Dollar spots - Small round spots of yellow grass appear in spring and fall.

- Ideal conditions: excessively damp ground.

- Do not water.

- Aerate and dethatch the lawn in the fall.

- Enrich the ground with compost.

- Fertilize every week with small quantities of a nitrogen-rich fertilizer in order to combat the damage caused by the disease.

Powdery mildew - Looks like white powder on top of the grass, especially on Kentucky bluegrass. - Avoid watering in the evening: water early in the morning.

- Allow the ground to dry between watering.

- Apply fertilizer.

- Aerate the soil in the fall.

Other organisms
Mushrooms (with stems) - Often flourish in soil that is slightly acidic and low in calcium.

- Often found on decomposing vegetal matter.

- Maintain a ground pH level that is above 6.5; spread dolomitic lime as needed.

- Remove the mushrooms by hand, in particular before cutting the grass in order to avoid spreading the spores.

- Aerate the soil in the fall.

To learn more about fighting against undesirable insects and diseases, you can visit:


How to create an unfriendly environment for undesirable plants

Learn to recognize undesirable plants; their presence often speaks volumes about the nature of your soil.

Undesirable plants

Conditions in which they flourish

Prevention and solutions other than pesticides

Common ragweed

Giant ragweed

To learn more about ragweed, you can visit Ministère de la Santé et des Services sociaux - L’herbe à poux, ça s’arrache! (available in French only)

- A sparse lawn.

- Freshly-turned or vegetation-free soil.

- New earth containing seeds.

- Vacant lots.

- Having a thick, healthy lawn reduces the chances that ragweed seeds will germinate.

- Mow regularly.

- Pull out the plant before it flowers in August.

- Organize and take part in an anti-ragweed campaign in your area.

Broadleaf weeds - Plantain tends to grow in poorly drained soil which has been trodden on by many people.

- Rough cinquefoil and red sorrel tend to grow in acidic soil.

- Woundwort and ground ivy prefer clay soil.

- Knotweed and European weed-sorrel flourish in compacted soil.

- Lamb’s-quarters takes root in a sparse lawn.

- Common mallow and purslane prefer soil with sparse vegetation.

- Pull out the undesirable plants by their roots.

- Spread mulch.

- Keep your grass thick and healthy.

- Use ground cover (lesser periwinkle, pachysandra, etc.) in shady places where the grass cannot grow densely.

- Spread corn gluten meal on a thriving lawn which prevents the seeds of certain undesirable plants from germinating.

- Make sure that the pH level is between 6 and 7; lime as needed to make the soil less acidic and thus less hospitable for certain plants.

Mulch is used in vegetable gardens, in flower beds as well as at the base of trees and shrubs in order to curtail the spread of weeds and to ensure that the soil remains damp.


Best organic mulching materials

Mulch thickness

Vegetable gardens and flower beds

Compost, leaves, sawdust, and lawn clippings

2.5 to 5 cm

Trees and shrubs

Wood chips or debarked chips

5 to 10 cm

Spread organic mulch on the soil surface; do not incorporate it into the soil. Add a new layer of mulch as the old layer decomposes naturally.

Do you wish to eliminate weeds before planting or eliminate those that thrive on grass-free surfaces (patio, garage walkway, etc.)?

Do your weeding manually by rooting out the entire plant. If not, use boiled water to destroy undesirable plants or a thermal weeding tool (for example, a propane flamer).

If necessary, use low risk herbicides such as acetic acid or a mixture of capric and pelargonic acids. Don’t forget that all vegetation is destroyed upon contact with these non-selective products.

House plants

Growing conditions for indoor plants are generally different from those they would find in their natural (often tropical) environments. It is therefore important to try to provide such plants with the light, humidity and temperature conditions that they require so that they remain healthy and better resistant to disease and insects. Start with the following essential guidelines:

  • When you purchase a plant, keep in mind the room in which you intend to place it:

    • Light is the most important aspect. Ideally, you should be able to provide the number of sunlight hours needed. If not, at least 3 hours of sunlight is sufficient for most plants requiring full sun or shade. East facing windows usually provide these conditions. For south or south-west facing windows, place plants further away from the glass. For north facing windows, add artificial light. You can also move your plants around, depending on the season. Place them in south facing windows in winter and north facing windows in summer. For example, hibiscus requires at least 4 hours of direct sunlight per day, so a north facing window would be inappropriate.

    • Humidity should be 50 to 60%.

  • Every plant has its own fertilizing and watering requirements, and they can vary depending on the time of year. Keep them in mind and remember that the key to successful plants is moderation in watering. Most plants prefer that the soil dry out between watering.

  • When you re-pot plants, generally in spring or as required, use sterile potting soil and choose the appropriate plant-specific type (cactus mix, African violet mix, etc.).

  • When you purchase a new plant, check it carefully for insects and disease. At home, keep it away from other plants for 3 weeks and check it regularly.

  • Avoid putting plants outside during the summer. If you do, it is better to re-pot before bringing a plant indoors in the fall. Be sure to (gently) remove all the earth and avoid damaging the roots. You should also mist the plant fully with water or insecticide soap. Keep the plant away from other plants for 3 weeks and check it carefully for insects and disease. If the plant develops a disease or has insects, remove the diseased portions or insects (with a cloth, cotton swab or brush) and spray the foliage.

  • You should generally check your plants every time you water them. Place any diseased or infested plants in quarantine and treat as required.

Problem insects: solutions house plants
Most common pests Alternatives to pesticides Pesticides: a last resport1
Aphids - Water with a powerful spray (e.g. use a showerhead).

- Insect sticky traps (yellow or white).

- D-phenothrin and tetramethrin
- Permethrin
- Pyrethrins 
- Resmethrin
- Rotenon
- Insecticide soap
- Insecticide soap and pyrethrins


- Insect tricky traps (yellow)

- D-phenothrin and tetramethrin
- Permethrin
- Pyrethrins 
- Resmethrin
- Insecticide soap
- Insecticide soap and pyrethrins

Spider mites Prevention: spray foliage regularly

- D-phenothrin and tetramethrin
- Pyrethrins
- Insecticide soap
- Insecticide soap and pyrethrins

Thrips - Insect sticky traps (blue or yellow) - Pyrethrins 
- Resmethrin
Scale insects Remove with an alcohol soaked cotton swab. - D-phenothrin and tetramethrin
- Rotenon
- Insecticide soap
- Insecticide soap and pyrethrins

1 Carefully follow the instructions provided on the label of the product.

Helpful hint

To avoid spraying pesticides into the air in your home, cover the plant with a plastic bag and spray through a small opening. Or, even better, treat the plant outdoors, weather permitting.


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