Treating bonsai tree fungus can be tricky. Because bonsai trees are so small and delicate, fungus can overtake and kill them very swiftly. Inspect your bonsai tree for signs of fungal infection every day so that, should one develop, you can catch it early. The main types of fungus that attack bonsai trees are all related to moisture and ventilation, and treatment is the same for all of them. Providing your bonsai tree with an ideal growing environment can really cut back on these incidents.
Inspect your bonsai tree daily for signs of fungal infection. Some symptoms include raised brown or orange spots on the underside of the tree's leaves, a powdery coating on the tree's leaves and trunk, clusters of black spots on the leaves and leaves yellowing and dropping off.
Use a disinfected pair of scissors to clip off all leaves exhibiting signs of fungal infection. To disinfect the scissors, soak a cotton swab in rubbing alcohol and rub it against the front and back of the blades. Disinfect the scissors again immediately after use to keep from spreading the fungus.
Spray the remaining healthy foliage with a fungicide that's specially formulated for bonsai trees. Repeat the fungicide treatment as often as is recommended by the manufacturer.
Try to avoid splashing water on the leaves of the bonsai tree when watering it, and dry any wet leaves immediately. Moisture can cause fungus to grow more quickly by spreading the spores.
Move the tree inside if it is outside. Rain and pests can further weaken the infected tree.
Dispose of any leaves that fall into the tree's pot immediately. The leaves might be infected with the fungus, and they can allow the mold to enter the soil.
Place the bonsai tree in an open, well-ventilated area to keep fungus from returning.