Both pests and diseases tend to appear out of nowhere, and before you know it, your precious bonsai plants are all but annihilated. A bonsai grower’s worst tragedy and naturally, must be avoided at all cost.

To that end, it is imperative to be prepared on what to do should a bunch of disgusting pests or a disease come a-calling. The best approach to bonsai-annihilating pests and diseases is prevention.

preventing pests and diseases from destroying a bonsai plant

Daily care and constant examination of your plant will make it easier for you to avoid a bug or infestation. Naturally, a healthy bonsai will survive an occasional bug, but a few insects can rapidly turn into a pest outbreak that can do heavy damage to your bonsai.

If you see a bug or two around your plant, use either an oil or soap-based insecticide and spray your plant every four to six days then monitor closely. Another effective way to protect your plant from bonsai tree bugs is identifying the kind of problem you’re dealing with.

There are many types of insects that can harm your tree, and identifying which is harming your bonsai and using the appropriate treatment keep your plant healthy.

Here are the common bonsai tree pests and diseases, and how you can protect your plant from them:

Pests

Aphids

a cluster of aphids on a bonsai leave

Also referred to as plant lice, aphids are the most common bonsai pests. Usually green or gray in color, but there are black and brownish red as well.

Aphids may carry viruses and diseases that could be transmitted to your plant as they suck out juices from your bonsai. An aphid infestation causes weak branches and curling leaves.

Basically, they enjoy sucking out the sap, damaging the leaves, and marking the foliage with a trace of sticky substance.

It is actually sugary substance which attracts ants and causes the growth of black sooty mold. Fortunately, aphids can be removed even without the use of insecticide—watering your plant regularly and spraying the undersides of its leaves will keep these pests away. If they insist on staying, spray or dust with malathion or pyrethrum.

Ants

Little piles of powdery soil will appear on the soil surface and under drainage holes. Use proprietary ant killer or water with pyrethrum liquid.

Boring insects

These leave a shiny trail on the surface of bark and bore right into the wood, in extreme cases killing a branch of tree. Fill the holes with DDT dust and seal them with wax and clay.

Caterpillars

Caterpillars can be very destructive to your bonsai since they feed off leaves. When you notice that the leaves of your tree have holes in them or appear eaten, check your plant from caterpillars—they can easily be removed by hand or by use of insecticides.

Earthworms

These can be tiresome and cause disturbance in the roots, especially if the containers have been plunged in the garden. Water with liquid pyrethrum or a proprietary worm killer.

Red Spider Mites

One of the most dangerous bonsai tree bugs, these pests are very difficult to spot because of their almost microscopic size. Symptoms of a red spider mite infestation include leaves turning yellow or brown and the appearance of very fine webs in between branches. Apply an organic soap spray or systematic insecticide to get rid of these pests.

Scale Insects

scale insects on a bonsai branch

Commonly found in clusters, these bonsai tree bugs will usually appear as brown, white or yellow bumps on your plant’s branches, leaves and trunk. They can be seen at any time of the year and will feed off your tree’s sap, causing its branches to droop and leaves to wilt.

You can try spraying or dust with malathion. Scale insect sometimes have a protective shell around them, which makes them difficult to remove by use of insecticides so it’s best to remove them by hand.

Slugs and Snails

Occasional use of slug bait in pellet form placed round the base of containers and on soil surface will control these disgusting pests.

IMPORTANT: Just remember that when using a new insecticide to protect your bonsai from a bug infestation, be sure to spray one leaf first to make sure the chemicals are not toxic to your plant.

Diseases

Mildew

This fungus appear as powdery white patches on the leaves. The leaves curl and become useless and young shoots gradually wither.

The bonsai tree’s sap gets drawn out by it and then during winter it spores over. Come spring, it materializes along with the buds and foliage. Spray with Karathane or another proprietary mildew spray.

Rust

It appears on the undersides of the leaves and induces elevated spots that are brown and orange in color. You’ll find them predominantly in beech as well as birch species of bonsai.

Black Spot

Bonsai of the Chinese Elm varieties are often affected by this type of fungi. On the leaves is where they will appear and in a conveniently noticeable clustered form. These black spots can actually change the color of the foliage into yellow and make the leaves fall off.

Other Damages

a damaged bonsai tree

There are a number of damages that could happen to a bonsai plant and these tend to happen by accident or by lack of bonsai care knowledge/experience.

Withered Leaves

This symptom may be caused by:

  • Lack of water
  • Too much water
  • Too strong a food moisture

Buds Dropping

  • This is usually caused by a lack of water when the buds are forming

Leaves Turning Brown

  • Scorch due to to hot sunlight on wet leaves—usually through glass
  • If your pet makes a habit of ‘watering’ your bonsai plant, it will gradually show signs of scorch

Also, if you happen to find dead leaves or branches, do remove it carefully with a sharp knife, scissors, pruning shears, according to thickness of the injured part. Sometimes a new shoot can be trained to replace one that needs to be removed, and occasionally the style of the tree may be altered to offset any serious damage.