Transcript plant physiological disorders

PLANT PHYSIOLOGICAL
DISORDERS
Introduction
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There are several symptoms that show on
plant leaves, stems and flowers that are not
caused by pests or diseases.
The main causes are:
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nutrient deficiencies,
excess fertilizer,
frost,
high temperature,
lack of light,
overwatering and
underwatering
Nutrient deficiencies
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Each nutrient (the commonest being
nitrogen, phosphorus, potassium, calcium
and magnesium) is required in the correct
amounts to enable the plant to carry out its
chemical processes.
When amounts present are too low,
deficiencies begin to show, usually by means
of leaf symptoms.
Provide regular applications of a suitable
fertilizer, especially during the summer
months and in situations where the roots are
restricted (as-in pots).
Blossom end rot
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In tomatoes and peppers, blossom end rot produces a
symptom of a black, concave lesion which looks at first sight
like a fungal disease.
It is caused by an imbalance between potassium and calcium
in the soil or compost.
It occurs most often when the soil or compost is allowed to
dry out while the fruits are swelling.
It is most common when plants are raised in grow bags,
where they have a small, shallow root run that dries out
easily.
Although there is no cure for blossom end rot once the
symptoms begin to appear, the obvious recommendation is
that fruiting crops should never be allowed to have dry roots.
Bitter pit in Apples
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Here the fruit develop many small, dark-brown, sunken pits .
The tissues below are stained to a depth of about 2 mm.
Cultivars such as 'Bramley's Seedling ' and 'Egremont Russet'
are most susceptible.
Young over-bearing trees show the worst effects.
The disorder is caused by low calcium levels in the fruit,
influenced by irregular water supply in the tree.
Ensure a steady water supply to the tree during dry spells.
Mulch around the tree to help moisture retention.
Summer prune young, vigorous trees especially when they
are holding too many fruit.
Occasionally use foliar sprays of calcium nitrate plus detergent
in the evening during summer to help prevent this problem.
Bitter Pit
Excess fertilizer
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When fertilizers are present at too high
levels, roots are scorched and are unable
to provide nutrients for the other parts of
the plant, often resulting in the plant's
death.
Careful consideration of the appropriate
frequency and amounts of fertilizer will
prevent this situation.
Low temperatures
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Plants differ in their tolerance
to low temperatures. Low
temperatures slow down the
plant's growth.
Frost often causes the above ground parts of sensitive plants
to collapse into a mess of
green tissue after ice has
formed inside the plant and
fractured all the cells.
High temperatures
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Plants may become exposed to
very high temperatures in
greenhouses, where growth may
be weak and ' leggy'.
Their leaves also may become dry
and brittle, especially if they are
touching the glass sides or roof of
the greenhouse.
Regular attention to ventilators or
the use of the automatic
ventilators avoids this problem.
Lack of light
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House plant species are sometimes placed in parts of the
house unsuitable for their ideal growth.
For example, a poinsettia needs high light levels.
Plants outdoors may be subjected to the same oversight.
Pelargoniums used as bedding plants should be given full
sunlight and will develop a pale foliage colour if placed in
a shady place.
lmpatiens, on the other hand , is able to withstand
considerable shade and maintain its rich dark -green
foliage.
Overwatering
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Overwatering replaces the air spaces in soil and
growing composts with water, thus preventing root
respiration which is needed to supply energy for root
growth and nutrient uptake.
Overwatering symptoms may include the following
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• The whole plant may wilt, the lower leaves turn yellow and
drop.
• New foliage may have brown spots.
• The whole plant may become stunted, and stems and roots
become brown and decayed.
Underwatering
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The plant needs sufficient water to carry nutrients around, to
be present as an ingredient for making sugar, to transpire
from the leaf in order to keep a desirable leaf temperature
and to maintain turgidity in some plant tissues.
In some plant species, leaves change from shiny to dull as a
first signal of water stress and also may change from bright
green to a grey green.
New leaves wilt, but in species such as holly and conifers only
the very youngest leaves will.
Underwatering
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Flowers may fade quickly and fall
prematurely. Older leaves often turn
brown, dry and fall off.
Digging a few centimetres into the soil
may indicate the need for watering
with shallow rooted perennials and
annual border plants.
Shrubs with deep roots rarely need
watering, although transplanted older
shrubs may show summer waterstress for a number of years.
Oedema
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Oedema is seen as raised corky spots on the
undersurface of leaves.
Species such as pelargonium, rhododendrons, begonias,
pansies, violets and some fleshy-leaved plants such as
Peperomia are affected.
Orchids can show oedema on their petals.
Oedema occurs when the roots' ability to supply water
exceeds the leaves' ability to release the water by
transpiration.
Oedema
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Conditions favouring oedema
occur most commonly in late
winter and early spring especially
during extended periods of cool,
cloudy weather. Warm, moist soil
occurring alongside cool, moist air
brings on the condition most
severely.
The symptoms are commonly
seen in unheated greenhouses.
The problem can be greatly
reduced by glasshouse heating
and automatic venting.