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Common Insect Pests

American Bonsai Society



(A primer for newcomers)

By Mike Blanton

The following information is provided to help newcomers care for bonsai, or any plant for that matter.  The list of pests is limited to those most commonly seen and is not intended to be exhaustive.  Everyone at one time or another has had an infestation of bugs on their plants and needed to take corrective action.  Plant sprays, particularly the organophosphate compounds are dangerous not only to pests, but to humans, pets and wildlife as well.  With that in mind, we recommend that the bonsai enthusiast use caution in their use and always consult a Nursery professional for help in selecting the right one for the job at hand.  Pest infestations can be reduced or greatly minimized when your trees are healthy, given plenty of air circulation around each plant and fertilized on a regular schedule.


We have provided many links to external sources in the listings so the visitor may conduct their own investigations on what types and kinds of pesticides may fit their needs and links to sites that provide poisoning symptoms as well as  product toxicity and regulatory information. Take your time doing your research and make sure you have the right equipment and protective clothing necessary to ensure your personal safety and those around you.

APHID (Homoptera) sap-suckers: piercing/sucking mouthparts


Description: Soft bodied, pear shaped, cornicles on their rear-end. When in clusters, they can be different colors but the green form is the most common.

Symptoms: Stunted and deformed new growth where populations concentrate.

Signs of infestation: Pest is easily seen, often along with honeydew or sooty mold. If you see ants harvesting honeydew from the Aphids, look for ant trails.

Hosts: Most plants with soft tender succulent new growth.(Brazilian raintree, Japanese quince, etc..)

Physical management: Many natural predators, parasites and fungi naturally exist to manage Aphids biologically. They can often be largely managed by washing them off with a garden hose.

Chemical control:  Diazanon, systemic acephate (Orthene Systemic), Ortho Malathion 50.  Insect spray’s and insecticidal soaps can also work well.

The following links are connected to the Pesticide Action Network (PAN) which should be consulted prior to using  acephate, Diazinon or Malathion 50

Follow the provided link for a more complete description of Aphids.

MEALYBUG (Homoptera) piercing/sucking mouthparts

Description: Soft-bodied sucking insects, close relatives of scale insects. Covered with powdery white or gray threads of wax.

Symptoms: Stunted and deformed new growth, chlorotic patches and weakened plants.

Signs of infestation: Found both on new growth and in leaf axils accompanied with honeydew or sooty mold.  Often found on or hiding under the bark of thick-barked trees.

Hosts: Most ornamental (Fukien tea, Nashia, Malpighia)

Physical management: Difficult to manage physically as they embed themselves into bark crevasse and other difficult-to-reach places.

Chemical Control: Malathion, Diazanon   - Spray the clusters of mealy bug completely to insure that you spray get in all the cracks and crevices of the bark.

The following links are connected to the Pesticide Action Network (PAN) which should be consulted prior to using  Diazinon  or Malathion

Follow the provided link for a more complete description of Mealy Bug.

SCALE (Homoptera) piercing/sucking mouthparts 

Description: Many shapes, sizes and colors.

Symptoms: Stunted, sickly plants, yellow chlorotic spots on upper leaf surface

Signs of infestation: Scales on underside of leaves, pick off to see if alive, soft scales usually  appear on twigs, leaf petioles and the underside of the primary leaf vein, honeydew/sooty mold.  Ants harvest the honeydew from live scale so look for ant trails.

Hosts: Many ornamentals are hosts for scale. Scale favorites are those plants with soft smooth bark that have highly water-retentive characteristics such as Podocarpus,  Bullhorn Acacia, Trident Maple, Citrus and  Olive.

Physical management: Small infestations can be remedied  by hand picking. Identifiying live from dead scale can be accomplished by sliding your thumbnail across a group of scales. If they are dry, hollow and flake off readily, they are dead. Live ones stick more firmly and are juicy when squashed.

Chemical control - acephate (Orthene systemic), carbaryl (Ortho Liquid Sevin), diazanon, malathion, dormant oil (Volck Oil Spray) alone or combined with carbaryl, acephate, diazanon or Malathion. Be sure to spray every nook and cranny on the plant including undersides of the  leaves.


The following links are connected to the Pesticide Action Network (PAN) which should be consulted prior to using  acephate   carbaryl   Diazinon    Malathion

Follow the provided link for a more complete description of Scale.

WHITEFLY (Homoptera) piercing/sucking mouthparts

Description: Tiny, snow-white flying insects that resemble moths if viewed under a magnifying glass. Without magnification, they look more like flying dandruff. (They are not moths: whiteflies are related to scale insects.)

Life Cycle: Adult female whiteflies lay eggs on the undersides of leaves. These hatch into nymphs, who crawl briefly and then settle down to suck plant juices. After a short pupa stage, adults emerge to feed and mate.

Symptoms: Leaf yellowing or mottling.

Signs of infestation: Flying “dandruff” and/or black sooty mold

Hosts: Many ornamentals. They seem to prefer plants that have hairy leaves (tomentose) and congregate on the undersides of the leaves during the daylight hours.

Physical management: None is recommend.

Chemical Control: Malathion, Diazanon or acephate (Orthene systemic). Insecticides easily eliminate whitefly adults and crawling nymphs. However, eggs, feeding nymphs and pupae defy insecticides. You must spray four times at four to six-day intervals to control nymphs as they hatch. Be sure to spray leaf undersides, where whiteflies congregate.

The following links are connected to the Pesticide Action Network (PAN) which should be consulted prior to using  Malathion   Diazinon     acephate

Follow the provided link for a more complete description of Whitefly.

BARK BEETLES AND TREE BORERS (Coleoptera) - chewing mouthparts

Description: Beetles and their larva (borers)

Life Cycle:  Adult beetles mate and then lay eggs in tunnels under tree bark. The eggs hatch into larvae, which make galleries as they feed. The fully grown larvae form pupae, which emerge as adult beetles.

Symptoms: Foliage or branches decline, particularly when the weather is hot. The tunneling of the larvae and adults severs the tree’s nutrient transport system. Equally damaging is the plugging of the water transport system by fungi introduced by the adult borers.

Signs of infestation: Shot-gun holes in the bark, sawdust, pitch or sap on tree stem branches, or low  down on the trunk. Signs of beetles.

Hosts: Conifers, Cypress, Ficus, Black Olive, Maple, Orange Jasmine and many members of the Prunus or Malus families.

Physical management: Once the tree is infected no good remedies exist.

Chemical Control: Drench bark surfaces with Lindane or Dursban. Spray anytime the beetles are active in your area every four to six weeks. Destroy infested branches by burning. One reported remedy from an ABS member is that Harold Sasaki recommended for pine borer is to take a fresh flea collar..., activate it and put it around the trunk, then encase the trunk & collar inside a plastic-bag or tent that keeps the chemical fumes inside. This can stay on for a long time.


The following links are connected to the Pesticide Action Network (PAN) which should be consulted prior to using  Lindane  or  Dursban (note: dursban is a trade name and there are many products each with different chemicals we have only slected one in this link)

Follow the provided link for a more complete description of Bark beetles

SPIDER MITES: (Arachnida) not insects, closely related to spiders and ticks

Description: Tiny spider like bodies that necessitates the need for magnification to see them -- two body parts, eight legs.

Life Cycle: In most areas of the continental United States mites complete their life cycle in seven to ten days at 80 degrees, so spray again in five or six days for three cycles to ensure getting the hatching eggs.

Symptoms: Tiny chlorotic spots (stippling), general yellowing, leaf drop can occur in serious infestations.

Signs of infestation: Mottled or generally sickly looking leaves on broad leaf plants.  Severely infected conifers often have a hazy white foliage appearance accompanied with semi-desiccated foliage in severe infestations. To verify that you have an infestation hold a clean, white sheet of paper under the sick plant leaf. Briskly thump the leaf several times. You should see several minute specks on the paper. With a pen, draw a tight circle around each speck. Now, wait. If the specks move out of the circles, then they are alive and treatment is necessary

Hosts: Junipers, fruit trees, azaleas.

Physical management: Mites are too small to manage physically

Chemical control: Kelthane, Diazanon, Malathion.  Make sure to spray the undersides of the leaves well, mites prefer to live in those places.


The links below are connected to the Pesticide Action Network (PAN) which should be consulted

Kelthane    Diazinon    Malathion  (note: Kelthane is a trade name and there are many products each with different chemicals we have only slected one in this link)

Follow the link provided for a complete description of Spider mites

FLEA BEETLES: (Coleoptera) chewing mouthparts 

Description: Tiny (1/16 inch) long bodies enlarged flea-like hind legs. They jump like fleas, though are no relation. Some are striped, but most are either black, brown or green. Larvae are small, slender and white with a black band.

Symptoms: Adults chew numerous small round holes in leaves of most vegetable crops as well as many flowers and weeds. Leaves appear to have been peppered with fine shot. When damage is heavy and there are many holes, leaves may wilt and turn brown. The host plant may become stunted and may even die. The larvae feed on roots or tubers.

Signs of infestation: Adult beetles. Begin control as soon as you first see damage in the spring.

Hosts: Serissa foetida , and many vegetables

Physical control: Not recommend due insect to size and mobility

Chemical control: Diazanon, Sevin, rotenone

The links below are connected to the Pesticide Action Network which should be consulted

Diazinon  rotenone   Seven

Follow the link profided for a complete description of flea beetles

LEAF MINER (Diptera)

Description: Flattened larvae of Diptera (flies)

Life Cycle:  Eggs are laid between the layers of the leaf, larvae hatch and tunnel while they feed, pupate outside the leaf and emerge as adults.

Symptoms: Leaves with squiggly discolorations in the form of lines (mines) - either winding (Serpentine) or blister (Blotch)

Signs of infestation: Visible mines on affected leaves. Sometimes pupa cases.

Hosts: Citrus, Severinia buxifolia (Orange Boxwood ), Schefflera, Azalea, Lantana, Bougainvillea

Physical management: Remove fallen leaves and burn

Chemical control: Orthene systemic

Follow the provided link for a complete description of leaf miners




Chewing - grasshoppers, caterpillars, beetles and  grubs resulting in bites and/or holes.

Piercing/Sucking - aphids, scale, mealybugs and whitefly cause stunting and discoloration.

Rasping/Slurping - mites and thrips scrape the epidermal layer and  lap out chlorophyll. Symptoms are called chlorosis (yellowing) or stippling (dot effect).

Miners (flies, moths) - lay eggs between layers of the leaf, larvae hatch and feed as they travel. They pupate inside leaf and emerge as an adult. (Serpentine or blotch paths)



Broad-Spectrum Insecticides – These types of insecticides control many pests in many situations. Diazanon is one such broad spectrum, eliminating over 100 different pests, including aphids, mealy bugs, mites, and flea beetles.

Specific Insecticides – Specific Insecticides are designed to control only one or two particular types of insects. For example, Dicofol was designed to kill only mites and will not affect other pests.

Systemic – Systemic insecticides are absorbed by the plant and move throughout the whole plant and therefore can kill any pest feeding on any part of the plant. Orthene and Avid are examples.

Note: Systemics should never be used on material that produces fruit or berries that an unattended child or wildlife  may be tempted to pick and consume.

Contact – Contact insecticides do not penetrate plant tissues. They kill any pest they physically land on, or any pest that feeds on plant tissues that have been sprayed. Malathion and  Sevin are examples.

Selective - More toxic to certain types of plants or animals. Kelthane for mites is an example









Mixing is the most dangerous time (when handling the concentrate) wear rubber gloves. Keep pesticide downwind of mixer and below eye level, mix only what you need (they lose effectiveness after mixed). Put the water in first and then add the chemical. Always follow the recommended rates. Do not eat, drink or smoke while mixing or applying. Never apply in an enclosed area like a greenhouse without a properly fitting mask with the correct breathing filters for the spray that you are using. (Masks are easily found at any good garden center.)

Once you have sprayed your bonsai, if you have leftover spray take the opportunity to use it in your garden landscape where appropriate.  Triple rinse the sprayer before you put it away.  Make sure you clean it thoroughly including any uptake hoses. Never pour excess spray down the septic system, sewer, storm drain or directly onto ground. Follow label instructions for the proper disposal of empty containers. When you’ve done all that you can take a shower and clean yourself as you did the sprayer -- everywhere. Wash your clothes promptly also.

You should also, alternate the pesticides you use to help prevent insect resistance.

Never use chemical weed killers in your sprayer.  Make sure and have a sprayer set aside for that purpose and have it clearly marked so you always use the right one.  The last thing you want is to mix them up and have dead bonsai.




 The two most commonly used and acceptable fungicides are sulfur and copper.

These are highly toxic to humans, other mammals, fish and aquatic invertebrates.

Fungicides act as protectants that inhibit the germination and growth of fungal spores.

Apply them  prior to periods of wet and humid weather when disease organisms can spread and grow easily. Since copper is a protectant, cover the entire plant surface to prevent invasion by disease organisms. Spray in the early morning when it is dry, the air is still and the sun is bright so that plants have time to dry. If the solution remains on leaves too long, it may penetrate the cuticle and kill the tissue.

Commercial Products: Bluestone (copper sulfate) Bonide Liquid Copper, Kocide, Top Cop, Top Cop with Sulfur


NOTE: Never apply oils within one month before or after applying sprays containing sulfur.


Oil Sprays

Prior to the 1970’s, orchardists sprayed their fruit trees each spring with heavy petroleum oils known as dormant oils, which killed over-wintering stages of insect pests before the growing season. It was important to spray before leafing out, since the heavy oil damaged leaves. Most of today’s horticultural oil spray are highly-refined, light oils. They contain fewer of the impurities that made the heavy dormant oils phytotoxic, so they can be used year-round on a variety of plants. These products are called superior, summer or supreme oils. They are especially effective at controlling pests like the scale because they spread thoroughly over the leaf surface. They work physically to smother and kill both pests and their eggs. Superior oils are unique because they control a broad variety of insect pests while going easy on beneficial insects.

Oils smother insects and their eggs. We use superior oils to control aphids, mealy bugs, mites and scales on a variety of fruit, nut, ornamental and shade trees. Cover both upper and lower leaf surfaces to reach the trunk and small branches. You cannot over apply oil unless you repeat a spraying after the first spray dries. Labels may provide directions for mixing in other pesticides, such as Malathion, for even more-effective growing season control, but only do so when recommended. Also check the label to make sure your tree is listed.  Certain plants and conifers should not be treated with oils.

Precautions: Do not apply oil when the temperature is lower than 40 degrees or higher than 80 degrees or if the humidity exceeds 90%, because these factors affect the oil’s evaporation and plants can be injured. Nor should you spray with oil 30 days before or after applying any type of sulfur spray or certain fungicides.

Commercial products: SunSpray Ultra-Fine oil, Volck Oil Spray.


Soap Sprays

Insecticidal soaps control insect pests by penetrating their cuticles, which causes their cell membranes to collapse and leak, resulting in dehydration. While some insects can overcome the effects of a soap spray, others are immediately affected and die.


•           Protection offered: soft-bodied insects like aphids, mealybugs, and whiteflies. (Non-toxic to humans, but will kill beneficial, so limit their use to problem areas.)


•           Household soaps that can be used: Ivory Snow, Ivory Liquid, Blue Dawn or Shaklee's Basic H. (Shaklee Basic H - mix 1 tablespoon per gallon.)


•           Soaps can be mixed with other insecticides, horticultural oil, pyrethrin and rotenone to boost their toxicity.

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