Ministère de l'Environnement
et de la Lutte contre les changements climatiques

Gardening … the all-natural way

2019 Edition

Alternatives to pesticides

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

 Undesirable organisms and their symptoms

Tips and tricks for prevention

 Alternatives to pesticides

Last resort: pesticides containing these active ingredients1

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 any 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 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 they 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, plastic cup or sheet of aluminum foil around the stem to at least 5 cm above ground level and pushed in to at least 3 cm beneath the surface (do not remove for 3 weeks)

–After sunset, using a flashlight, remove cutworms

–D-trans allethrin




–Ferric phosphate

Colorado potato beetles (“potato bugs”)

–Feed on potato leaves.

NB Not to be confused with ladybugs, which are useful insects

–Plant garlic or marigold between rows since they repel potato beetles. –Eliminate by hand; remove the masses of orange eggs found under leaves (usually in June).

–Water leaves with a powerful spray to dislodge the bugs.

–Pluck up larvae and adult insects in April, May and September


–Fond of damp, dark places

–Generally easy to catch

–Easier to spot at night, when they are more active

–Avoid accumulating plant and wood debris

–Work the soil on warm dry days in spring; This will disturb adults and uncover their eggs

–Set about 20 traps per lot, wherever you spot the pests

–Use “tunnel” traps of all sorts of 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 over soapy water

–Diatomaceous earth

–Insecticide soap



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

–May transmit viruses.

–Foster the proliferation of predators, such as ladybugs and lacewings

–Use the right amount of fertilizer; too much nitrogen-based fertilizer promotes the growth of succulent tissue that attracts aphids

–If possible, dislodge the aphids with a powerful spray of water once a day

–Insecticide soap



White grubs (chafer larvae) –Turn over soil and if you uncover them continue digging deeper around the entire area; remove 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
Lily leaf beetles Check lilies regularly at 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 will sometimes drop to the ground to escape your vigilance  
Common Scab

–Brown scabs are found on potatoes, beets, turnips, etc. and when soil is highly alkaline (pH 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 white patches on potatoes and tomatoes

–Enrich soil using well decomposed organic matter

–Choose resistant plant varieties

–Avoid spraying leaves with cold water


1 Follow the instructions on the label of the product.


Solutions to the problem of undesirable organisms that damage your trees and shrubs

Undesirable organism

Affected trees and shrubs and their symptoms

Alternatives to pesticides

Last resort: pesticides containing these active ingredients1

Aphids –Many species can be 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 cause plant death

–Trim the shrub before treatment, as needed

–If possible, water daily with a powerful spray to dislodge the aphids

–Foster the proliferation of predators such as ladybugs and lacewings

–Use the right amount of fertilizer; too much fertilizer promotes the growth of succulent tissue that attracts aphids

–Insecticide soap

–Mineral oil


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

–Caterpillars feed on leaves

–Ants do not harm trees. They are attracted by, among other things, aphid excretions. In return, ants protect aphids from their enemies

–Install strips 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 tunnel underneath 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. Little mounds of sawdust on the trunk point to the entrance of the tunnel

Apple maggots –Apple trees

–Microscopic larvae leave grooves in the apple

–Pick up fallen fruit 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 with red apple-shaped disks (5 traps per tree, 1.5 m above the ground. Lay traps after the flower petals fall)

Scale insects –A number of different species can be affected –When there has been a proliferation, cut down the affected branches to reduce insect numbers –Insecticide soap


–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 (“gouting”) on the trunk and infested branches. The larvae tunnel underneath the bark

–Since borers usually attack weakened trees, keep trees healthy with fertilizer and irrigation during dry spells

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

–Call a specialized pest removal company
Birch leaf miners     Generally, pesticides are called for only when a tree is affected by severe infestation several 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 with a stick when they return to their nests late in the evening or during cool spells Bacillus thuringiensis kurstaki (B.t.k.)
Leaf roller caterpillars

Hide in rolled leaves

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 that causes leaves to shrivel and form witchbroom Witchbroom can be pruned  
Apple Scab
(caused by a fungus)
Apple trees

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

–Avoid vulnerable varieties (Gala, Delicious, Jerseymac, McIntosh and Cortland) and choose scab-resistant varieties such as Liberty, Jonafree, Prima, Freedom and Spartan, or Dolgo, Evereste, Liset and Makamik crab-apples

–Remove leaves in autumn, to remove fungus infestation sites

–Reduce dampness by leaving space between plants

–Trim the tree for better aeration

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

–From mid-June to mid-July, 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 and burn the bark

–After pruning, disinfect tools with rubbing alcohol or methanol

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

–Black spot is characterized by 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 dead leaves as soon as they fall in order to prevent infestation sites of this fungus from forming



Bacillus subtilis strain QST 713

Powdery lilac mildew

Fungus on the top part of the leaves generally appears during August Gather and destroy the leaves in the fall No treatment is needed for minor infestations

Black knot 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 tree trunks, this fungus penetrates the bark through machine-made gashes It’s important to thoroughly protect the bark  

Fire blight
Often found on mountain ash and from time to time on hawthorns, apple–trees and cotoneasters of the family of Rosaceae plants

  Ask for resistant varieties when purchasing  

1 Follow the instructions on the label of the product.


Solutions to problems of undesirable organisms damaging lawns

Harmful organism

Symptoms or damage

Alternatives to pesticides

Insects and undesirable plants
See the Residential lawn care section (in French only)
Diseases (fungi)
Dollar spots –Small round spots on yellow grass appear in spring and fall

–Ideal conditions: excessively damp ground

–Do not water

–Aerate and dethatch the lawn in the fall

–Enrich ground with compost

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

Powdery mildew –Looks like white powder on top of the grass, especially common 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 above 6.5; spread dolomitic lime as needed

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

–Aerate the soil in the fall

Learn more about fighting undesirable insects and diseases at:


Creating an unfriendly environment for undesirable plants

Learn to recognize undesirable plants; they speak volumes about the nature of your soil.

Undesirable plants

Conditions in which they flourish

Prevention and solutions other than pesticides

Common ragweed

Giant ragweed

Learn more about ragweed at Qué–Reconnaître et limiter l’herbe à poux (available in French only)

–A sparse lawn

–Freshly-turned or vegetation-free soil

–New earth containing seeds.

–Vacant lots

–A thick, healthy lawn reduces the chances that ragweed seeds will germinate

–Mow regularly

–Remove plants before they flower 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 frequently trodden

–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 sparse lawns

–Common mallow and purslane prefer soil with sparse vegetation

–Pull out undesirable plants by their roots

–Spread mulch

–Keep your grass thick and healthy

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

–Spread corn gluten meal on a thriving lawn to prevent the seeds of certain undesirable plants from germinating

–Make sure that the pH level is between 6 and 7; add lime as needed to make the soil less acidic and less hospitable to certain undesirables

Mulch is used in vegetable gardens, flower beds and at the base of trees and shrubs to curtail the spread of weeds and ensure that 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 mix 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 like patio, decks and garage walkways?

Weed manually by uprooting the entire plant or apply boiling water or use a thermal weeding tool like a propane flamer.

If needed, you can use low risk herbicides like acetic acid and herbicidal soap. Don’t forget that all vegetation is destroyed by non-selective chemicals.

House plants

Growing conditions for indoor (often tropical) plants are generally different from those they would find in their natural environments. It is therefore important to try to provide such plants with optimal light, humidity and temperature conditions that they require to remain healthy and more 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 factor. Ideally, you should be able to ensure the recommended number of hours of sunlight. If this is not feasable, at least 3 hours of sunlight is usually sufficient for most plants that requiring full or partial sun. 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, choosing south–facing windows in winter and north-facing windows in summer. For example, hibiscus requires at least 4 hours of direct sunlight each day, so a north-facing window would be inappropriate.

    • Humidity should be between 50 and 60%.

  • Every plant has its own individual fertilizing and watering requirement that can vary depending on the time of year. Keep that in mind and remember that the key to happy plants is moderation in watering. Most plants like the soil to dry out between watering.

  • When you re-pot (generally in spring or as required), use sterile potting soil and choose the right 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 preferable 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 fully mist the plant with water. 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, cut away the diseased portions and remove insects with a cloth, cotton swab or brush then 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 for house plants
Most common pests Alternatives to pesticides Last resort: pesticides containing these active ingredients1
Aphids –Water with a powerful spray (e.g. a showerhead)

–Yellow or white insect sticky traps

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


–Yellow insect sticky traps

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

Spider mites Prevention: spray foliage regularly

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

Thrips –Blue or yellow insect sticky traps –Pyrethrins 
Scale insects Remove with a cotton swab soaked in alcohol –D-phenothrin and tetramethrin
–Insecticide soap
–Insecticide soap and pyrethrins

1 Carefully follow the product label instructions.

Helpful hint

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


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