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A
symptom is a plant’s visible
reaction to the presence of a
biotic or
abiotic causal
agent or
disease.
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The fact that
diseased plants are in
some way different from
healthy plants indicates that there are ways
of recognizing plant diseases and the terminology used for
description of plant symptoms is really quite simple, not at all
like that of, say, human medicine.
Plant diseases are frequently
given their common names based on the plant part
affected, by the
way the plant is affected, or by the cause of the
disease.
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Symptoms of plant diseases
include some general types:
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| 1)
Hypertrophy
(Overdevelopment) of
tissue |
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| 2)
Hypotrophy
and/or atrophy
(Underdevelopment) of
tissue. |
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| 3)
Death of
tissue. |
- Spots: A "spot" is a relatively small, distinct
lesion, with definite borders. Most times, we indicate the
plant organ affected when describing a plant disease symptom.
For example, if the spot is on leaves, it is called a "leaf
spot". If the spots are on fruit, it is naturally a "fruit
spot".
- Blights: As spots grow and
coalesce, the symptoms
may well be described as a "blight". There are gradations from
spots to blights and the better term to use may not always be
clear.
- Cankers: again, found mostly on stems and branches,
are sunken
lesion.
- Rots: Rots occur when
tissue breaks down. Rots lead
to a slimy, wet "mush". However,
dry rots can occur.
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| 4) Problems with
water uptake |
- Wilts: Wilts occur when plants droop.
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A good home gardener recognizes
symptoms of plant diseases quickly and takes steps to
prevent or
control them. Hoverer the extremely large number of plant
diseases (over 50,000) makes it impossible for any one person to
be familiar with all of them but, there are certain facts that
help in the identification of plant diseases. The most important
is to know the name of the plant that is affected. One can then
check known plant diseases to see if a similar condition has
ever been reported on that plant.
Useful tip to identify plant disease:
- Foliage symptoms:
Foliage on plants
infected with a bacterium or fungus
will normally develop first on the older leaves. Virus symptoms
develop on the younger leaves.
If it occurred in a very short time (overnight), it is probably
not a parasitic disease, but is more likely due to some
unfavourable environmental condition or chemical.
- Parasitic
diseases: Symptoms due to a parasitic
attack usually do not affect a large percentage of
the plants in the early stages, but start in one area and
gradually spread to the other plants. And, parasitic diseases
usually do not affect several different kinds of plants in one
area at one time, even though some disease organisms can
attack many different plants.
There is often a tendency for gardeners to immediately
suspect a disease when a leaf turns yellow or brown. But, it may
just be a normal response. Even
evergreens lose their leaves
eventually. |
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