Page 96 - Tài liệu Ebook cây cảnh Bonsai Basics

98 HEALTHY BO SAl

DISEASES

This heading covers a number of prob-
lems which can affect the life of a plant,
causing it to wither and eventually die.
We generally distinguish between fungal
diseases, deficiency diseases caused by
an imbalance in plant nutrients, and
bacterial and viral diseases (the latter
usually incurable and fatal to the in-
fected plant).
Although fungal growth is looked on
with misgiving, it should be remembered
that some fungus is not only harmless
but beneficial. For instance, fine white
mycelium growing around the roots
should be encouraged as it is in certain
cases a sign of good health.

Powdery mildew
This is certainly the most widespread
Powdery mildew is a hmgal disease which covers the fungus disease. It shows itself in the form
whole plant in a downy white deposit. of a white, floury layer which gradually
spreads over the shoots and leaves.
The mycelium (equivalent to a root
system) of the fungus draws sap directly
from the plant's cell tissues which sub-
seq uently die. This fungus generally
thrives in a hot, humid, poorly ventilated
atmosphere and is encouraged by an
excess of nitrogen.
Some specific treatments are available
to deal with this fungus, most of them
sulphur based. Use them to prevent the
disease, especially where conditions fa-
vour the development of the fungus. Be
careful not to wet the foliage over much,
as this is a frequent cause of mildew.

Rust
Another common fungal disease, which
occurs in the form of orange or brown
patches or even blisters spreading over
the underside of the leaves, which curl up
and eventually drop. These patches and
Many treatments, whether insecticides or fungi-
blisters result from infection by the
cides, can be sprayed on with a good vaporizer which
gives an Cl'CU spray. Phragmidium fungus, which also thrives