Keep harmful insects away from your growing space

🌿 Naturally fight pests in indoor and outdoor cultivation 🌱

Introduction

Crops, whether indoors (🏡 greenhouses, verandas, grow-rooms) or outdoors (🌻 vegetable gardens, gardens), often face harmful insects called pests. 🐜 Aphids, 🕷️ mites (red spiders), thrips, 🪰 whiteflies, and 🐛 caterpillars are among the most frequently encountered pests in cultivation.

Rather than resorting to chemical pesticides, it is possible to protect plants naturally and ecologically. This article offers preventive methods to avoid infestations, as well as effective natural treatments against various pests, suitable for both indoor and outdoor use. Each solution is accompanied by usage advice, targeted pests, and precautions to be both clear and educational.

✅ Prevent pests naturally

Prevention is the first step in effective pest control. By adopting good cultural practices, the environment becomes less favorable to pests, greatly reducing the risk of infestation. Here are some natural preventive techniques, valid both indoors and outdoors:

✨ Soil mulching (mulching)

Organic mulching at the base of plants protects the soil and limits pests. Mulching consists of covering the soil with organic materials (straw, bark, grass clippings, dead leaves...) or mineral materials. This protective layer provides multiple benefits: it maintains good soil moisture, prevents water stress that can weaken plants, and regulates soil temperature (useful outdoors during heat or cold spikes). Indirectly, mulched soil is more fertile and balanced, making plants more vigorous and less susceptible to attacks. Moreover, mulching limits the growth of weeds that could serve as refuge or food for certain pests. Finally, a thick mulch can form a physical barrier for soil insects.

⚠️ Precaution: Avoid mulch that is too thick or waterlogged as it could encourage slugs and snails (other vegetable garden pests). Indoors, large containers or planters can be mulched (with clay pellets, coconut fiber...) to maintain moisture, while monitoring that no pests hide there.

🔄 Crop rotation

Outdoors (vegetable garden, open ground), practice crop rotation from one year to the next. This means not replanting plants of the same botanical family in the same place immediately. By changing the location of vegetables and flowers each season, the cycle of pests specific to a given plant is disrupted. For example, if a plot has been invaded by cabbage white butterfly caterpillars, avoid replanting cabbages there the following year: residual eggs or larvae will no longer find their host plant and will not be able to proliferate. Similarly, rotation helps prevent soil diseases. In indoor cultivation (soilless, containers), this principle can be applied: do not always grow the same variety in the same substrate, or replace/substitute the substrate between two crops to eliminate possible pest eggs.

⚠️ Precaution: Follow a 3 to 4 year rotation for sensitive vegetables (tomatoes, cabbages, leeks, carrots…), to completely break the cycle of specialized pests.

🌸 Companion plants and biodiversity

Some companion plants can repel pests or divert them from your main crops. This is an effective companion planting technique especially outdoors or in greenhouses. Here are some practical examples:

• 🌼 Marigolds (Tagetes)
  Marigolds emit a strong odor that repels several insects and soil parasites. They are known to reduce harmful nematodes and repel certain insects while attracting pollinators. They are often planted in the middle of the vegetable garden, among the vegetables.

• 🌺 Nasturtium
  Nasturtium is used as a trap plant for aphids: it strongly attracts them, which will colonize its stems and leaves rather than your important crops (roses, vegetables). You then just need to remove or destroy the infested nasturtium.

• 🧄 Garlic, onion, chives (Alliaceae)
  These sulfur-containing plants have a general repellent effect. Planted at the base of roses, tomatoes, or lettuce, they can bother aphids, flies, and fungal diseases.
  (Your article already contains two garlic-based tips: garlic infusion and olfactory barrier, so we will not go into detail here.)

• 🌱 Basil, mint, rosemary, and aromatic herbs
  These herbs release fragrant essential oils that disrupt harmful insects. For example, basil planted near tomatoes helps repel whiteflies and thrips, while peppermint repels aphids and ants.

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🐝 Attracting auxiliary insects

In addition to repellent plants, you can also sow attractive plants (trap plants) to divert pests' attention or attract their natural predators.

👉 Nectar- and pollen-rich flowers such as phacelia, borage, cosmos, chamomile, or sunflower attract ladybugs, hoverflies, parasitic wasps, and other beneficial auxiliary insects. These predatory insects will then help limit pests.

👉 Indoors or in a greenhouse, place pots of aromatic plants or nectar-rich flowers near crops or at the entrance to enjoy the same benefits.

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🌡️ Climate control and hygiene

Environmental conditions play a crucial role in pest proliferation, especially indoors where the ecosystem is limited. Here are some important preventive measures:

💧 Humidity

• Maintain appropriate humidity.
• Example: red spider mites (tetranychids) love dry air. Regularly spraying water around plants (especially under leaves) increases humidity and slows their spread.
• Be careful though: excessive stagnant humidity can promote fungus gnats (sciarids) and certain fungal diseases. So find a good balance and ventilate if necessary.

🌬️ Temperature and ventilation

• Ventilate greenhouses and enclosed spaces to avoid excessive heat and stale air, conditions that favor whiteflies and fungal diseases.
• Good air circulation limits fungal spores and hinders fragile flying insects.
• In indoor cultivation, using oscillating fans helps strengthen stems while discouraging flying insects from settling permanently.

🧹 Hygiene and maintenance

• Regularly disinfect your growing equipment (stakes, pruning tools, reused pots) to avoid transmitting eggs or pathogenic germs from one plant to another.
• Indoors, quarantine new plants or cuttings for a few days to detect and treat any pests before introducing them into the main area.
• Frequently remove dead or diseased leaves, as they often harbor insects and molds.
• Avoid leaving plant debris on the ground, in the garden or greenhouse.

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🔍 Regular monitoring

Inspect frequently:

• The top and underside of leaves 🍃
• New shoots 🌱
• Flower buds 🌸

🔍 Regular monitoring

Inspect frequently:

• The top and underside of leaves 🍃
• New shoots 🌱
• Flower buds 🌸

Early detection of the first pests (aphids, scale insects, butterfly eggs, mite webs) allows quick action before a population explosion.

• Use yellow or blue sticky traps 🟡🔵 to detect early whiteflies, thrips, etc.
• Manually eliminate at the first signs: crush a few aphids, remove a caterpillar, or shower a plant infested with thrips to prevent their reproduction.

⚠️ This vigilance is even more crucial indoors, where pests have no natural spontaneous predators!

🌿 II. Natural treatments against pests

Despite all precautions, infestations can occur. Fortunately, there are many biological treatments to fight targeted pests without polluting or compromising the health of your crops.

Below we present proven natural remedies – plant extracts (manures, infusions), homemade solutions (black soap, oils) or use of beneficial insects – with their respective effectiveness, targeted pests, and precautions for use.

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🍃 Nettle and horsetail manures

Plant manures are fermented extracts of macerated plants, widely used in organic gardening. Two classics are nettle manure and horsetail manure, with complementary properties:

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🌿 Nettle manure (Urtica dioica)

It is a versatile preparation, both fertilizing and insect-repellent. Used as a diluted foliar spray, nettle manure is an effective natural repellent against aphids and mites. It also strengthens plant defenses thanks to its richness in minerals, making them less susceptible to diseases.

💡 Preventive use:

• In spring, spray a dilution (~10% manure) on the foliage to discourage aphids from attacking.

💪 Curative use:

• Spray diluted nettle manure directly on a plant infested with aphids or red spiders.
• Its smell and compounds disturb pests and can cause them to drop off or flee.

🐛 Targeted pests :

• Aphids (all species)
• Mites and red spiders
• Whiteflies (moderate effectiveness)
• Soft-bodied insects

⚠️ Precautions:

• Never apply pure manure (undiluted) on leaves: it is very concentrated and can burn the plant.
• Avoid treatments during full bloom (the very nitrogen-rich nettle manure could disturb it).
• Do not treat in full sun (risk of phytotoxicity).
• Indoors, apply sparingly (strong fermentation odor) and ventilate after treatment.

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🌾 Horsetail liquid manure (Equisetum arvense)

Horsetail is rich in silica and alkaloids. Its liquid manure is mainly known as a preventive fungicide (against downy mildew, powdery mildew, rust…), but it also has an interesting insect-repellent action.

🦠 Usage :

• Alkaloid substances help repel or combat certain insects like the leek moth (leaf miner), as well as mites and red spiders.
• Use as a diluted foliar spray (~10–20%) on sensitive crops:
• Potatoes 🥔
• Tomatoes 🍅
• Rose bushes 🌹
• Leeks
• Delicate fruit trees 🍏
• Renew approximately every 2 weeks during risk periods.

🐛 Targeted pests :

• Mites (spider mites)
• Specific garden insects (leek moth, possibly cabbage flea beetles)
• Fungal diseases (downy mildew, rust, powdery mildew...)

⚠️ Precautions:

• Respect the recommended dilutions (~1 part of liquid manure to 5 parts of water according to recipes).
• Shake the mixture before use, as it may settle.
• Preferably apply in the evening or in cloudy weather to maximize effectiveness.

💡 Bonus tip :
Horsetail can also be used in decoction (quick extraction by boiling), which extracts silica and alkaloids more quickly.
👉 To be used fresh – not preservable unlike manure.

🧄 Garlic: a formidable natural repellent against garden insects

Garlic is a valuable ally in the garden! Thanks to its sulfur compounds, garlic acts as a natural repellent against many pests, including aphids, whiteflies, and certain beetles. Here are two simple and effective techniques to take advantage of its insect-repelling properties.

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🌿 Technique 1: Garlic infusion for direct spraying

This method protects plants by applying a garlic infusion directly to their foliage.

🔧 Matériel nécessaire :

• 5 to 6 cloves of garlic
• 1 liter of water
• A sprayer

🧪 Preparation steps:

1. Peel and crush the garlic cloves.
2. Bring the water to a boil, then reduce to low heat. Add the garlic and let infuse for 10 to 15 minutes.
3. Let cool, then filter to remove the pieces of garlic.
4. Pour the infusion into a spray bottle.
5. Spray on leaves, stems, and areas affected by insects (including the undersides of leaves).

💡 To be renewed every 4 to 5 days in case of persistent infestation.

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🌬️ Technique 2: Olfactory barrier based on garlic, lemongrass, and vinegar

This version acts as a preventive barrier by diffusing an unpleasant odor for insects, without directly treating the plants.

🔧 Matériel nécessaire :

• 5 cloves of garlic
• 1 liter of water
• 1 tablespoon of lemongrass essential oil
• 2 tablespoons of white vinegar or cider vinegar
• A sprayer

🧪 Preparation steps:

1. Prepare a garlic infusion as in the first method.
2. Once cooled, add citronella oil and vinegar.
3. Mix well, then pour into a sprayer.
4. Spray around cultivated areas or at greenhouse entrances, without watering the plants directly.

💡 Ideal for protecting crops preventively, especially indoors or under a greenhouse.

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🧼 Black soap spray

Black soap is a grandmother's remedy still relevant today for eliminating harmful insects. It is a natural soap (soft soap made from vegetable oils and potash) that is diluted in water and sprayed on infested plants.

🔬 Action: Black soap works by direct contact:

• It wets and strips the thin protective greasy layer of insects, causing them to dry out.
• It forms a sticky film that blocks their respiratory openings (spiracles).

🪲 Effective against:
Aphids, whiteflies, scale insects, thrips, mites, psyllids…
These soft-bodied insects are quickly eliminated by a black soap treatment.

🌱 Usage :

• Dilute liquid black soap in warm water (~5 tablespoons per liter of water, or follow the product instructions).
• Once cooled, spray this soapy water on and under the leaves, targeting pest colonies carefully.
• You can also soak a cloth with this solution and manually clean the affected leaves (useful against scale insects that stick to stems).

💡 Note:
Black soap is used both indoors (houseplants, greenhouses) and in the garden. It is biodegradable and safe for the user, pets, and plants – if used properly.

🎯 Targeted pests :

• Aphids of all kinds
• Whiteflies
• Scale insects (including mealybugs)
• Thrips (adult and larval forms)
• Mites (red spiders)
• Psyllids

❌ Limits :

• No effect on insects hidden in tissues (e.g., leaf miners)
• Ineffective on hard-shelled insects (adult beetles, adult butterflies)

🔁 Effectiveness and frequency :

• Shock treatment but short duration, without insecticide residue
• May require several treatments
• In case of heavy infestation:
• Spray for 2 to 3 consecutive days
• Then once a week until disappearance
• Rinse the plant with clear water between applications (to remove shed skins and sticky honeydew)

⚠️ Precautions:

• Always test the solution on a small part of the plant (some ferns, orchids, succulents are sensitive)
• Do not apply in direct sunlight or in hot weather (magnifying glass effect)
• Treat at the end of the day
• Indoors, you can rinse the foliage a few hours later to avoid sticky residues
• Black soap does not spare beneficial insects if they are present during spraying:
• Do not treat when ladybugs 🐞 or other allies are present
• Or isolate the plant to be treated

🛢️ Natural oils (Neem oil and essential oils)

Insecticidal vegetable oils form another category of organic treatments.

• The best known is Neem oil, extracted from the seeds of the neem tree (Azadirachta indica), renowned for its broad-spectrum insecticidal power.
• Other essential oils (EO) obtained by distillation of aromatic plants can also serve as natural insect repellents or insecticides: mint, lavender, geranium, citrus 🍋, tea tree, etc. They often act through their strong smell or compounds that disrupt pests.

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🌿 Neem Oil

It is a plant-based pesticide used for over a century to protect crops.

🧪 Active ingredient :

• The azadirachtin it contains disrupts the growth and reproduction of many insects.

🎯 Effective against :

• Aphids
• Whiteflies
• Thrips
• Mites
• Caterpillars
• Leafhoppers
  (And other garden pests)

It also acts as:

• Anti-appetent
• Hormone disruptor
• With an additional moderate antifungal action

🌱 Usage :

• Mix a few milliliters of Neem oil with warm water
• Add a little black soap or Marseille soap to emulsify
• Spray on foliage, both top and underside of leaves
• Treat preferably in the evening
• Repeat every 7 to 10 days if necessary (gradual effect)

⚠️ Precautions:

• Shake the mixture well before use, as the oil separates quickly
• Do not overdose: a concentration of 0.5 to 2% is sufficient
• Do not apply in direct sunlight
• Although considered safe for mammals, it is recommended to:
• Wash treated vegetables before consumption
• Wear gloves during preparation

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🌼 Essential oils (EOs)

Many EOs have insect-repellent or insecticidal properties thanks to their volatile active ingredients. Here are some examples:

• 🌿 Peppermint essential oil
  Insecticide and repellent recognized against aphids and other garden insects.
  Its strong menthol scent disturbs aphids and can even limit their establishment on neighboring plants.

• 🍊 Sweet Orange essential oil
  Very effective at repelling whiteflies and red spider mites, thanks to limonene that it contains.

• 💜 Lavender (or Lavandin) essential oil
  Traditionally used to repel aphids and ants, especially around rose bushes.

• 🌺 Geranium rose oil
  Contains geraniol and citronellol, composed effective against scale insects and aphids.
  It is a natural insecticide that can kill these pests by ingestion and inhalation of its volatile compounds.

• 🌳 Tea Tree Oil
  Mainly antifungal, its camphoraceous smell can also repel insects and sanitize affected plants of scale insects or fungi.

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🧴 Use of essential oils

⚗️ Important : Never use pure essential oils, they can burn plants.

🧪 Basic recipe :

• Dilute 5 to 10 drops of the chosen essential oil (or a blend of several complementary essential oils) in 1 liter of water
• Add 1 to 2 drops of black soap or dishwashing liquid as an emulsifier
• Shake well
• Spray on attacked plants, targeting hotspots (aphids, scale insects...)

🕐 Ideal time :

• Since EOs are very volatile, it is best to treat in the evening or early morning
• Repeat 3 days later, then weekly as needed

⚠️ Precautions:

• Wear gloves and avoid directly inhaling the mixture
• EOs can be irritating to the skin or respiratory tract
• Do not treat in the presence of bees 🐝 (some EOs like mint can also repel them)
• Avoid prolonged use of the same EO to prevent stressing the plant
• Always check that the chosen essential oil (EO) is not phytotoxic to your plant species
  👉 Perform a preliminary test on a few leaves

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🧪 Plant decoctions and macerations

(Tomato, rhubarb, tansy...)

In addition to garlic (already discussed in the article), many garden plants can be used to make homemade insecticidal preparations. These decoctions, infusions, or macerations allow targeting specific pests with local natural resources. Here are three effective recipes:

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🍅 Tomato leaves

Tomato stems and leaves contain tomatine, an alkaloid with insecticidal properties.

💧 Possible preparations :

• Tomato manure (fermented maceration of suckers)
• Tomato leaf decoction

🎯 Effectiveness :

• Natural repellent and insecticide
• Allows to get rid of certain pests:
• Cabbage white butterfly (butterfly and caterpillars) 🦋
• Flea beetles (small jumping beetles) 🪲
• Leek moth
• Carrot fly 🥕
• And acts by contact on aphids

🛠️ Usage:

1. Boil 500 g of tomato leaves in 5 L of water
2. Let infuse while cooling
3. Filter
4. Spray the cold, pure decoction on infested plants (e.g., aphid colonies)

✨ Tip:
You can add a spoonful of black soap and a bit of 70° alcohol to improve adhesion and enhance effectiveness.

⚠️ Precaution:
Tomato is part of the Solanaceae family and contains potentially toxic alkaloids:

• Wear gloves during preparation
• Avoid consuming treated plants without prior washing

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🍃 Rhubarb leaves

The large rhubarb leaves, not edible for humans (toxic because of oxalic acid), can become a formidable natural insecticide.
A rhubarb manure (or a 24h maceration followed by a decoction) is used undiluted in spraying as an insect repellent from the arrival of the first pests.

🎯 Target:

• Aphids (black bean, rose green, etc.)
• Parasitic flies (carrot, onion)
• Leek moth
• Slugs 🐌

✅ Usage:

1. Soak ~500 g of chopped leaves in 5 L of water for 24h
2. Bring to a boil for 20–30 min
3. Let cool, filter
4. Spray directly on attacked plants (e.g., infested rose bushes)

⚠️ Precautions:

• Wear gloves (do not rub eyes during preparation)
• Do not water edible soil with this preparation (oxalic acid can disrupt soil microbial life)
• Do not store too long: the manure tea is more effective fresh

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🌼 Tansy (Tanacetum vulgare)

Tansy is a wild plant with yellow flowers, known for its repellent properties.
It contains thujones and other powerful aromatic compounds, released in infusion or manure tea.

🐜 Effective against :

• Ants
• Aphids
• Flies (carrot, onion)
• Flea beetles
• Whiteflies
• Mites
• And more...

🌱 Tip :
Scattering cut tansy between vegetable rows helps disrupt insect detection.

💧 Insecticidal action:
A concentrated tansy infusion can inhibit egg laying and block larval development of certain pests:

• Colorado potato beetles 🪲 (potato beetles)
• Codling moths (fruit worms)
• Cabbage whites 🦋

✅ Usage:

• Infuse 300 g of fresh tansy (leaves + flowers) in 1 L of boiling water for 24h
• Or let ferment for 1 week in a manure tea
• Spray diluted at 10–20% on plants
• You can also place bunches of tansy at the base of fruit trees 🍏 to protect them during pest flight periods

⚠️ Precautions:

• Tansy can be irritating to the touch ➤ wear gloves when harvesting
• Its effect is mainly repellent, complementary to other methods (e.g., traps or trap plants)

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🐞 Beneficial insects (biocontrol allies)

A ladybug devouring aphids is a valuable natural ally against infestations!

🌿 Rather than killing pests directly, an ecological approach is to introduce their natural enemies to do the work for you. These organisms are called beneficial insects or crop auxiliaries.

• Outdoors: encourage their natural arrival with flowered areas, hedges, insect hotels, wild corners
• Indoors / greenhouse: you can buy and introduce specific beneficial insects on infested plants

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🐞 Ladybugs (and their larvae)

Ladybugs are great devourers of aphids.
The seven-spotted ladybug is well known: a single adult or larval individual can consume up to 100 aphids per day.
They also sometimes attack other small insects like scale insects or psyllids.

✅ Usage:

• In the garden, attract them naturally with nectar-rich flowers 🌸
• Avoid pesticides
• In case of an invasion, you can buy larvae and place them on the infested plants – they will immediately get to work!

⚠️ Precautions:

• Release them in the evening or early morning
• Slightly moisten the plants beforehand ➤ they will drink and stay more willingly
• Indoors, once adults, ladybugs may try to leave ➤ use them mainly in closed greenhouses

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🌿 Lacewings (Chrysoperla carnea, “golden-eyed lady”)

Lacewing larvae are voracious predators, capable of eating:

• 50 aphids per day
• But also thrips, small caterpillars, whiteflies…

👉 They are nicknamed “aphid lions”.

✅ Usage:

• You can buy eggs or larvae
• Place them in infested areas (garden or greenhouse)
• Adults become pretty green insects and feed on pollen (harmless)

⚠️ Precautions:

• Lacewings are nocturnal ➤ don’t be surprised if you don’t see them during the day
• Do not apply black soap or oil in the areas where you have released them, as it may kill them

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🕷️ Predatory mites – Specialists in red spiders and thrips

These are tiny carnivorous mites (e.g., Phytoseiulus persimilis, Amblyseius swirskii) that feed on other mites or insects.
They are the natural enemies of spider mites (red spiders) and also attack thrips.

✅ Usage:

• They are mainly introduced in greenhouses or indoor cultivation
• You buy sachets or tubes containing these live mites
• They are spread on infested plants, where they actively seek out harmful colonies to devour
• Some like A. swirskii can be used preventively against thrips and whiteflies

⚠️ Precaution:

• These mites like some humidity
  ➤ If the air is too dry (< 50%), mist the foliage a little
• Avoid treatments with sulfur or oils, which are harmful to them

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🛡️ Predatory bugs – Against thrips, whiteflies, caterpillars

Small carnivorous bugs like Orius laevigatus (the "pirate thrips") or Macrolophus are used in greenhouse crops to control:

• Thrips
• Whiteflies (aleurodes)
• Caterpillars
• And sometimes even mites

🔬 They sting and empty their prey 🧪

✅ Usage:

• Often used by professional market gardeners, but also suitable for amateur gardeners in greenhouses
• Introduce them as soon as the first thrips are spotted
• Orius is also effective on indoor plants

⚠️ Precaution:

• These bugs can fly
  ➤ Outdoors, they risk leaving
  ➤ In a greenhouse, they remain in the closed ecosystem

🪱 Entomopathogenic nematodes – Trap soil pests

They are not insects, but microscopic useful worms (genus Steinernema or Heterorhabditis) that parasitize insect larvae in the soil.

🎯 Main targets:

• Gray worms (cutworm larvae, caterpillars in the soil)
• Larvae of fungus gnats (sciarids)
• Pupal stages of thrips fallen on the ground
• White grubs on the lawn
• Soil worms in the vegetable garden

✅ Usage:

• Buy a packet of live nematodes (in powder form to dilute)
• Water the infested soil with this solution
• Nematodes enter insect larvae and eliminate them

⚠️ Precautions:

• Respect temperature and humidity conditions (generally:
  ➤ soil > 12°C,
  ➤ treatment at the end of the day,
  ➤ moist soil)
• Nematodes are harmless to the environment, except for targeted insects

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🐝 Other useful natural allies

Other auxiliaries also deserve to be mentioned:

• Hoverflies 🪰: their larvae eat aphids
• Parasitoid wasps 🐝:
  • Encarsia formosa against whiteflies in greenhouses
  • Trichogrammes against pest butterfly eggs
• Insectivorous birds 🐦: love caterpillars in gardens

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⚠️ General precautions with beneficials

If you introduce useful insects, here are some recommendations to avoid compromising their effectiveness:

🚫 Avoid insecticidal treatments, even organic (black soap, oils...), just after introduction ➤ this could kill your allies.
✔️ Apply these treatments before their arrival, then let them act naturally.

💧 Provide a welcoming habitat:

• Leave some aphids on an isolated plant to feed the ladybugs
• Maintain good humidity for predatory mites
• Plant flowers rich in nectar and pollen 🌼 to feed the adults of many beneficials (ladybugs, lacewings, hoverflies...)

🌿 Result: your beneficials will establish themselves sustainably and naturally and effectively prevent the return of pests.

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🐛 Summary table: Common pests & natural solutions (Prevention – Treatments – Beneficials)

 

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