Page 177 - Tài liệu cây cảnh Bonsai4me Bonsai Basics

Chapter 23 A Basic Guide to Pests

and Diseases That Affect Bonsai

Most species of shrubs or trees commonly used for bonsai cultivation rarely
succumb to disease if looked after carefully and given the correct environment to
grow in.
It is my experience that 95% or more trees that are affected by disease or
bugs are also in poor general health. Under or over watering, under or over
feeding, poor growing conditions (including poor, compacted soil), poor
positioning of the bonsai, all cause stress to a tree, leaving it more susceptible to
infection from disease and bugs. Bugs can attack trees randomly though you
quickly learn which are likely to become infested at a moments' notice! Whilst
healthy, vigorous trees are unlikely to be attacked, they will also be better able to

survive attacks from bugs and diseases. Trees in poor health or trees that are
under stressful growing conditions will be more affected by any external attack
on its weakened defences.
Precautions such as regular spraying with systemic insecticides and
fungicides can be useful though should be relied upon. Systemic remedies work
by being sprayed onto the foliage, which digests the treatment into the sap
stream of the plant where it is distributed throughout the entire plant. Attacks of
fungi or bugs are quelled when they attack the plant and are exposed to the
treated sap. However, systemic treatments are not 100% effective and regular
spraying is expensive, environmentally unsound; repeated use can also reduce
the effectiveness of treatments when they are actually needed. In my opinion, it
is far better to use systemic insecticides or fungicides on trees that are known to
suffer problems at certain times of the year.

Primarily, try to identify what has happened to your tree. Has it lost foliage?
Do any of the leaves have discolouration or holes? Closely examine the tree and

the foliage, is there any evidence of pests either on the tree itself, on the surface
of the compost or around the surface on which the pot itself is standing.
Secondly, once (hopefully) the pest or disease is identified and dealt with it is
important to identify if there is any way that you could prevent re-occurrence in
the future. Some problems such as caterpillars and aphids are difficult to guard