Common Pesticides & Fungicides for Bonsai: When & How to Use

General Tips & Disclaimers§

Below is a reference table summarizing common pest‐ and disease‐control products (insecticides, fungicides, oils, etc.), typical use cases, and general applicability across the four main bonsai categories—Pines, Junipers, Deciduous, and Tropicals. Example brand names are listed to help you identify products in garden centers, but always read the label carefully and follow local regulations.

  1. Always Read Labels: Ensure the product is labeled for your target pest/disease and plant type. Follow recommended rates, intervals, and safety precautions.
  2. Test Spray: For delicate species (especially tropicals with thin leaves or certain maples), do a small test application to check for phytotoxicity (leaf burn).
  3. Environmental Conditions:
    • Temperature: Many oils and soaps must be used below ~85 °F to avoid leaf scorching.
    • Timing: Spraying in early morning or late evening helps avoid quick evaporation and scorching under intense sun.
    • Rain: Reapply fungicides or soaps if rain washes them off.
  4. Combine Approaches: For scale or severe mites, a systemic insecticide plus horticultural oil can be more effective than either alone. For persistent fungal issues, a systemic fungicide plus contact fungicide might be needed.
  5. Watch Pollinators: Imidacloprid and other systemics can harm bees if the bonsai flowers. Consider non-chemical or contact treatments if pollinators frequent your tree.
  6. Cultural Fixes: Many pest/disease outbreaks stem from over/underwatering, poor airflow, or weak sunlight. Improving these conditions often reduces pest pressure and helps any chemical treatment succeed.

Use these tables as a guide when deciding which product type might help your bonsai's particular pest or disease situation. Adjust for your local climate, each tree's sensitivities, and label directions. When in doubt, consult an experienced bonsai professional or local extension office for a precise diagnosis and recommended treatment plan.

Table 1: Product Compatibility by Tree Species§

Product / Active Ingredient Example Brands Use on Pines Use on Junipers Use on Deciduous Use on Tropicals
Systemic Insecticide(e.g., Imidacloprid, Dinotefuran) – BioAdvanced Tree & Shrub (Imidacloprid)– Bonide Systemic Granules - Effective for pine scale or mealybugs on needles/branches. - Can help control some pine borers (if labeled for borers) when used early. - Great for scale or serious aphid problems on junipers—often the best approach because the juniper's scale foliage is hard to penetrate with contact sprays.- Less effective on spider mites unless specifically labeled for mites. - Handles aphids, scale, mealybugs on deciduous. Systemic means new leaves are protected. - Often used if repeated contact sprays have failed or if leaves are too dense for thorough coverage. - Scale, mealybugs, whiteflies, thrips on tropicals. Very useful indoors where you want minimal spraying on foliage.- Many "tree & shrub" formulations specify ornamental/tropical usage—check label.
Horticultural Oil(e.g., Mineral oil, "Dormant oil") – Bonide Horticultural Oil– Volck Oil– Sunniland Dormant Oil - Safe for most pines if used at recommended temperatures (usually <85 °F). - Helps reduce scale/aphid eggs on needles or bark crevices in dormant season. - Commonly used as a dormant spray for juniper scale eggs or spider mite eggs. - In growing season, can help smother active scale crawlers or mild mite problems, but thorough coverage is crucial. - Perfect for overwintering pests on deciduous bark. A single dormant oil spray in late winter can drastically cut aphids/scale come spring.- Summer usage is possible but watch for leaf burn if temps exceed label threshold (often 80–85 °F). - Helpful for mealybugs, scale crawlers on tropicals, but be mindful of high temperatures—oil can cause leaf burn above ~85 °F.- Test on a few leaves first, especially for sensitive species like fukien tea or thin-leaf ficus.
Neem Oil(Azadirachtin or Clarified Neem) – Garden Safe Neem Oil– Bonide Neem Oil - Good for mild aphid/scale on pines. - For pine needle cast fungus, results vary—copper or chlorothalonil might be more effective for severe infections. - Frequent choice for spider mites or scale if you catch them early. Re‐spray regularly. - Helps with some juniper fungal issues like mild tip blight, but stronger fungicides are needed for heavy infections. - Popular for powdery mildew, black spot on maples, roses, etc., as well as aphids & mealybugs. - Often part of an organic IPM approach. - Great for indoor tropicals with mild scale/mealybugs, or early spider mite issues. - Also handles fungal leaf spot if not severe.
Insecticidal Soap(Potassium salts of fatty acids) – Safer Brand Insecticidal Soap– Natria Insecticidal Soap - Can help with mild aphid or mite outbreaks on pine candles, but thorough coverage of needles is tricky. - Less effective if pine foliage is too dense or pests are hidden. - Good choice for juniper spider mites if you can physically contact them. - For scale, it mainly kills the "crawler" stage; established adult scale shells are protected. Combine with horticultural oil or systemic for best results. - Very common for aphids, whiteflies, thrips, and spider mites on tender deciduous leaves. - Gentle if used as directed; rinse off or reapply after a day or two. - Ideal for indoor tropical outbreaks—safe to use around the home if label permits. - Great initial approach for mild pests. Check leaves in 1–2 weeks, reapply if pests reappear.
Contact Fungicide(e.g., Copper, Chlorothalonil) – Bonide Liquid Copper (copper)– Daconil (chlorothalonil)– Fung-onil (chlorothalonil) - Use for needle cast (e.g., Daconil for pines) or tip blight. Reapply as new needles emerge. - Copper can be used dormant or early-season, but can cause slight phytotoxicity if used in high heat or repeated. - Juniper tip blight or rust can be treated with chlorothalonil or copper. - Apply early when new growth is most vulnerable. Re-spray as recommended if the fungus persists. - For leaf spot, anthracnose, mildew on maples, elms, fruiting species. - Copper can also target bacterial blights. But watch for leaf burn if temps are high. - Less commonly needed for tropicals unless mildew or leaf spot is severe. Then a copper or multi-purpose fungicide can help. - Always test on a small area if the species is sensitive (thin-leaf ficus, etc.).
Systemic Fungicide(e.g., Thiophanate‐methyl, Propiconazole) – Bonide Infuse (Propiconazole)– Cleary's 3336 (Thiophanate‐methyl) - For severe pine needle blight or root rot in waterlogged soil, a systemic drench might help. Follow label for conifer usage. - Juniper root rot or advanced tip blight can sometimes be halted with a drench or trunk spray. - Some systemics list junipers on the label—check if tip blight/rust is covered. - Commonly used for root rot (phytophthora) or advanced leaf spot in ornamental trees. - Apply as a root drench or foliar spray. This can save a valued deciduous bonsai if caught early. - Tropical "wet-foot" rot, anthracnose, or black spot can be tackled with certain systemics. - Check the label for "indoor ornamental" or "tropical plant" approval.
Dormant Spray (Lime–Sulfur) – Bonide Lime–Sulfur - Can be used on dormant pines to suppress needle cast spores in winter. Avoid applying to green new needles. - Helps kill overwintering juniper rust spores or tip blight fungus on dormant branches. - Must not be used once new soft growth appears—risk of burn. - Common on fruit trees for peach leaf curl or fungal cankers. On bonsai, it helps reduce overwintering spores if used in late winter. - Don't apply to leaves—do it while they're dormant. - Rarely used on tropicals since they don't go dormant. Also can be too harsh on evergreen tropical foliage.

Table 2: Product Usage Details§

Product / Active Ingredient Example Brands Primary Targets & When to Use Notes & Application Tips
Systemic Insecticide(e.g., Imidacloprid, Dinotefuran) – BioAdvanced Tree & Shrub (Imidacloprid)– Bonide Systemic Granules - Scale, aphids, mealybugs, whiteflies, some borers- Absorbed through roots or trunk, protects new growth from inside.- Usually applied as a soil drench or granules; lasts several weeks to months.- Good for hidden pests (scale under bark) or heavy infestations. - Application: Usually poured at base of trunk or mixed into topsoil, then watered in.- Timing: Early spring to catch pests as they emerge, or mid-season if you see scale/aphids.- Caution: Systemic insecticides can affect pollinators if the tree flowers—avoid if bees are foraging.
Horticultural Oil(e.g., Mineral oil, "Dormant oil") – Bonide Horticultural Oil– Volck Oil– Sunniland Dormant Oil - Smothers eggs & soft‐bodied insects: scale crawlers, aphids, mites, mealybugs, overwintering eggs.- Often used as a dormant spray in late winter/early spring to kill overwintering pests.- Summer application can also control active infestations if label allows. - Application: Spray thoroughly on bark, foliage (top & underside), trunk.- Timing: Dormant application for overwintering pests; or in mild/cool hours if used in summer. - Caution: Do not apply if extremely hot, freezing, or to water‐stressed plants. Some labels advise avoiding use 2 wks before/after sulfur or certain fungicides.
Neem Oil(Azadirachtin or Clarified Neem) – Garden Safe Neem Oil– Bonide Neem Oil - Broad‐spectrum insect/fungus control: aphids, spider mites, scale crawlers, powdery mildew, black spot. - Has some systemic-like properties in certain plants. Also a repellent for some chewing insects. - Repeated applications needed (every 7–14 days). - Application: Spray leaves/needles thoroughly (top & underside), plus stems. - Timing: Repeat weekly or biweekly until pests are gone. - Caution: Sensitive plants can get leaf burn in direct sun/heat. Apply in cooler part of day. - Some neem products combine insecticidal soap. Check label for safe intervals and if reapplication is necessary.
Insecticidal Soap(Potassium salts of fatty acids) – Safer Brand Insecticidal Soap– Natria Insecticidal Soap - Contact kill for aphids, mealybugs, young scale crawlers, spider mites. - Works only on direct contact—no residual protection. - Reapply every 5–7 days while pests are active. - Often used in combination with oils or systemic for comprehensive control. - Application: Spray thoroughly where pests are visible (undersides of leaves, new shoots). - Timing: Early morning or evening so it doesn't evaporate too fast. - Caution: Some plants can be sensitive; do a test spray. No long residual, so repeated sprays are essential. - Often used in tandem with horticultural or neem oil.
Contact Fungicide(e.g., Copper, Chlorothalonil) – Bonide Liquid Copper (copper)– Daconil (chlorothalonil)– Fung-onil (chlorothalonil) - Fungal leaf spots, needle casts, anthracnose, powdery mildew, tip blight. - Copper is an older broad-spectrum that can help with bacterial issues, rust, mildew. - Chlorothalonil good for many foliar fungal diseases on ornamentals & conifers. - Typically protective; reapply if rain washes it off. - Application: Spray leaves/needles thoroughly to create protective barrier. - Timing: Start early in disease cycle, reapply every 7–14 days or as label directs, especially after rain. - Caution: Copper can stain or burn if used in high temps (>85 °F). Chlorothalonil is broad-spectrum but follow label rates carefully. Keep away from fish/aquatic habitats if label warns.
Systemic Fungicide(e.g., Thiophanate‐methyl, Propiconazole) – Bonide Infuse (Propiconazole)– Cleary's 3336 (Thiophanate‐methyl) - Penetrates plant tissue to combat root rots, systemic mildews, leaf spots from inside. - Good for persistent or severe fungal infections that contact fungicides don't fully control. - Often used as a drench or trunk spray. Reapplication intervals vary (14–28 days). - Application: Often a soil drench or foliar spray. Make sure product is labeled for your plant type and disease. - Timing: Early detection is best. Some systemics also work prophylactically if your collection is repeatedly hit by the same fungus. - Caution: Always confirm the fungus is listed on the label. Some systemics might not cover all diseases. Handle carefully—these can be potent chemicals.
Dormant Spray (Lime–Sulfur) – Bonide Lime–Sulfur - Mainly for overwintering fungal spores (anthracnose, peach leaf curl, rust) & some insect eggs. - Often used on leafless deciduous or fully dormant conifers. - Strong odor (sulfurous), can bleach or damage fresh foliage if used incorrectly. - Application: Spray thoroughly in late winter / early spring before bud break. - Caution: Highly phytotoxic to green tissues—only apply on dormant branches. The sulfur smell is strong, so do it outdoors. - Sometimes used to treat deadwood for bleaching/bug control, but keep away from live tissues.

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