- Powdery Mildew: A fungus infection on the top of your bonsai tree
leaves; usually the result of a lack of air circulation combined with evening watering on the leaves.
- Downy Mildew: A grey covering on the underside of the leaves with yellow spots on the top of the leaves will conduct in (poor circulation and wet soil is at fault); this infection could be avoided by keeping the humidity as low as it is necessary.
- Chlorosis: When bonsai trees leaves are yellowish and veins remain green. This is an iron deficiency. This disease can be treated with chelated Iron. It is important to treat your bonsai soil with iron as a regular routine rather than wait for problems to occur.
- Sooty Mold: This is a black mold of older plants and can result in an aphid infestation. If you don’t treat this in time with fungicide, your bonsai will be killed.
- Root Rot: If your bonsai tree soil is too wet, will cause root rot occurrence. In order to heal your bonsai you must remove the rotted roots and change the soil. You need also to revise your watering technique so that the soil does not remain so wet. Keep fertilizer to a minimum until your plant health has improved.
- Aphids: You always can get rid of these at bay by showering them off. Place yellow sticky around the plants to attack the flying stage of this and other insects.
- Scales: The bonsai tree keeper must scratch off or use alcohol on a swab.
- Spider Mites: If your plant is infected by spider mites, your plants are in serious danger. You MUST wash the plant once every 10days for 3 cycles to try to eliminate. A miticide may be needed.
- Whiteflies: Again you need to use the yellow sticky cards and wash with soap.
- Mealy Bugs: The same useful method: Use alcohol on a swab.