Virus, Bacteria, (II) Environmental
Fungi, Actinomycetes, Diseases
Nematodes (Temperature, pH, Rainfall,..)
(i) Macronutrients (ii) Micronutients
(C, N, P, K, Mg, Ca) (Cu, Zn, B, Mo)
(I) Physiological (nutritional deficiency)
(i) Macroelements (N, P, K, Mg, Ca)
Nitrogen (N) – a major element needed by
all green plants. It is transported from older
growth to new growth.
Under nitrogen deficiency, chlorotic (yellow color) symptoms and light red cast can be
seen on the veins and petioles of leaves: the older mature leaves gradually change from
their normal characteristic green appearance to a much paler green. As the deficiency
progresses these older leaves become uniformly yellow over the entire leaf including the
veins. Leaves approach a yellowish white color under extreme deficiency. The young
leaves at the top of the plant maintain a green but paler color and tend to become smaller
Branching is reduced in nitrogen deficient plants resulting in short, spindly plants (long
week stem with poor root development).
Phosphorus (P) – an important mineral that
stores energy in plants, also a flowering agent.
The P-deficient leaves show some necrotic spots.
A major visual symptom is that the plants are dwarfed or stunted: Phosphorus deficient
plants develop very slowly in relation to other plants growing under similar
environmental conditions but without phosphorus deficiency. Some species such as
tomato, lettuce, corn and the brassicas develop a distinct purpling of the stem, petiole
and the under sides of the leaves. Under severe deficiency conditions, there is also a
tendency for leaves to develop a blue-gray luster. In older leaves under very severe
deficiency conditions a brown netted veining of the leaves may develop.
Potassium (K) – a nitrogen catalyst
needed for enzyme manufacture.
K-deficient leaves show marginal and tip necrosis (burn and dead), others at a more
advanced deficiency status show necrosis in the interveinal spaces between the main veins
along with interveinal chlorosis. Under sever conditions, wilting and drying of the plant due
to poor water uptake.
Magnesium (Mg) – is important in
photosynthesis and the chlorophyll molecule
where light energy is converted to chemical
energy. Chlorophyll gives plants their green
The Mg-deficient leaves show advanced interveinal chlorosis, with necrosis developing in
the highly chlorotic tissue. In its advanced form, magnesium deficiency may superficially
resemble potassium deficiency. In the case of magnesium deficiency the symptoms
generally start with mottled chlorotic areas developing in the interveinal tissue. The
interveinal laminae tissue tends to expand proportionately more than the other leaf tissues,
producing a raised puckered surface, with the top of the puckers progressively going from
chlorotic to necrotic tissue. Later, leaf tips curl, entire plant turns yellow and dies.
Magnesium is mobile and is transported from older to newer growth. Old growth is
affected first. In some plants such as the Brassica, tints of orange, yellow, and purple may
Calcium (Ca) – helps form the structural
parts of the plants (it is a major element in
The very low mobility of Ca is a major factor determining the expression of
Ca-deficiency symptoms in plants. The Ca-deficient leaves show necrosis around the
base of the leaves (soft dead necrotic tissue at rapidly growing areas), which is
generally related to poor translocation of calcium to the tissue rather than a low
external supply of calcium. Very slow growing plants with a deficient supply of
calcium may re-translocate sufficient calcium from older leaves to maintain growth
with only a marginal chlorosis of the leaves. This ultimately results in the margins of
the leaves growing more slowly than the rest of the leaf, causing the leaf to cup
downward. This symptom often progresses to the point where the petioles develop but
the leaves do not, leaving only a dark bit of necrotic tissue at the top of each petiole.
Abiotic Diseases (cont.)
(I) Physiological (nutritional deficiency) (cont.)
(ii) Microelements (Cu, Fe, Zn, S, B, Mo)
Copper (Cu) is needed in only small
amounts. This metal aids in plant
metabolism and general health. It helps
ward off disease and pests, aids in the
utilization of iron and the manufacture
These Cu-deficient leaves are curled, and their petioles bend downward. Copper
deficiency may be expressed as a light overall chlorosis along with the permanent loss
of turgor in the young leaves. Recently matured leaves show netted, green veining with
areas bleaching to a whitish gray. Some leaves develop sunken necrotic spots and have
a tendency to bend downward.
Trees under chronic copper deficiency develop a rosette form of growth. Leaves are
small and chlorotic with spotty necrosis.
Iron (Fe) – is an important constituent
of enzymes and plays a role in
The Fe-deficient leaves show strong chlorosis (yellow) at the base of the leaves with
some green netting. The most common symptom for Fe-deficiency starts out as an
interveinal chlorosis of the youngest leaves (low mobility of Fe), evolves into an overall
chlorosis, and ends as a totally bleached leaf (white). The bleached areas often develop
necrotic spots. Up until the time the leaves become almost completely white they will
recover upon application of iron. In the recovery phase the veins are the first to recover
as indicated by their bright green color. This distinct venial re-greening observed during
iron recovery is probably the most recognizable symptom in all of classical plant
Zinc (Zn) – is needed in small
amounts for growth and chlorophyll
The Zn-deficient leaves show an advanced case of interveinal necrosis. In the early stages
of zinc deficiency the younger leaves become yellow and pitting develops in the
interveinal upper surfaces of the mature leaves. As the deficiency progress, these
symptoms develop into an intense interveinal necrosis but the main veins remain green, as
in the symptoms of recovering iron deficiency.
In many plants, especially trees, the leaves become very small and the internodes shorten,
producing a rosette like appearance (short stem internodes).
Sulfur (S) – is a building block of
amino acids and proteins. Used in
small amounts, it aids transpiration
and transport of other elements.
The S-deficient leaves show a general overall chlorosis while still retaining some green
color. The veins and petioles show a very distinct reddish color.
The visual symptoms of sulfur deficiency are very similar to the chlorosis found in
nitrogen deficiency. However, in sulfur deficiency the yellowing is much more uniform
over the entire plant including young leaves. The reddish color often found on the
underside of the leaves and the petioles has a more pinkish tone and is much less vivid
than that found in nitrogen deficiency. With advanced sulfur deficiency brown lesions
and/or necrotic spots often develop along the petiole, and the leaves tend to become
more erect and often twisted and brittle.
Boron (B) – is needed in small
amounts. Boron aids in cell
division and in transporting
sugars through cell walls. It also
aids in forming the amino acids
thymine and cytosine, important
to DNA synthesis.
The B-deficient leaves show a light general chlorosis. The tolerance of plants to boron
varies greatly, to the extent that the boron concentrations necessary for the growth of
plants having a high boron requirement may be toxic to plants sensitive to boron. Boron is
poorly transported in the phloem of most plants (affects new growth first), with the
exception of those plants that utilize complex sugars, such as sorbitol, as transport
metabolites. The B-deficient causes "Heart rot" in beets and "stem crack" in celery.
Molybdenum (Mo) – a catalyst
needed in small quantities. It is
involved in nitrogen fixation
(assimilation) and in the
manufacture of enzymes.
The Mo-deficient leaves show some mottled spotting along with some interveinal
chlorosis. An early symptom for Mo-deficiency is a general overall chlorosis, similar to
the symptom for nitrogen deficiency but generally without the reddish coloration on the
undersides of the leaves. At high concentrations, molybdenum has a very distinctive
toxicity symptom in that the leaves turn a very brilliant orange.
In the case of cauliflower, the lamina of the new leaves fail to develop, resulting in a
characteristic “whiptail appearance” (long, narrow and severely twisted, but not tightly
Abiotic Diseases (cont.)
(Sunlight, Humidity, Temperature, pH,
Chemical addition, Rainfall, Soil texture)
D. deremensis 'Warneckii' is subject to notching, a condition affecting marginal tissue
near the leaf base. This condition is apparently due to high temperatures. Apical
necrosis caused by rapid increases in temperature in foliage plants was first described
in 1961. The tested plants were not damaged at 15.5 or 35ºC (60 or 95ºF), but raising
the temperature from 15.5ºC to 35ºC resulted in apical necrosis or blackening of new
The symptoms are characteristically greasy-looking, water-soaked lesion, developing
within 48 hours of exposure and affecting old leaves most severely.
Cold or cool environments (2-8ºC) can severely damage tropical plants. Temperatures
that are safe for many other crops cause some injury in some foliage plant. Exposure to
these temperatures results the development of white, sunken, irregularly shaped lesions.
Cold injury is more severe in plants receiving high levels of nitrogen and potassium than
in plants receiving lower levels of these nutrients.
Direct sunlight exposure
necrosis (burn and dead)
Drought can broadly be defined as a low water availability that limits or prevents
growth. The severity of drought depends on the duration. Symptoms of drought stress
begin with a bluish color, followed by leaf rolling and eventual browning. Drought
stress also can be observed as localized dry spots that appear as irregular patterns of
dead and dying leaves.
When too much fertilizer is applied, the nutrient balances in grass plants or soil systems
disrupt so, excessive growth is favored, which may result in scalping damage (“burn” or
desiccation of leaf tissues).
Many pesticides used for weed control and turfgrass disease control, and other pest
management chemicals, have growth regulating properties. Misapplication of
pesticides may cause injury or irregular growth.
Pesticide injury is easily differentiated from disease and insect injury. Generally the
damage will appear in a pattern that corresponds to the method of application and
includes broad to narrow streaks, corresponding to overlapped application or other
regular patterns. Specific signs of this type of injury include lack of pest control,
turfgrass chlorosis, leaf speckling and death. These symptoms can develop quickly
after application or several weeks later.