I. Symptoms appearing first or most severely on new
growth (root and shoot tips, new leaves, flowers, fruits,
buds) |
A. Terminal bud usually dies. Symptoms on new
growth. |
1. Basal part of young leaves and internal
tissues of organs may become necrotic.
One of the earliest symptoms is failure of the root tips to
elongate normally. Terminal shoot meristems also die giving rise
to a witchs broom. Young leaves become very thick,
leathery, and chlorotic; in some species young leaves may be
crinkled because of necrotic spots on leaf edge during
development. Young leaves of terminal buds become light green
then necrotic and stem finally dies back at terminal bud. Rust
colored cracks and corking occur on young stems, petioles, and
flower stalks. "Heart rot" of beets, "stem crack"
of celery... boron deficiency |
2. Necrosis occurs at tip and margin of
leaves causing a definite hook at leaf tip.
Calcium is essential for the growth of shoot and root tips
(meristems). Growing point dies. Margins of young leaves are
scalloped and abnormally green and, due to inhibition of cell
wall formation, the leaf tips may be "gelatinous" and
stuck together inhibiting leaf unfolding. Stem structure is weak
and peduncle collapse or shoot topple may occur. Roots are
stunted. Premature shedding of fruit and buds is common.
Downward curl of leaf tips (hooking) occurs near terminal bud.
ammonium or magnesium excess may induce a
calcium deficiency in plants... calcium deficiency |
Differentiating between calcium and boron
deficiency symptoms: When calcium is deficient, there is a
characteristic hooking of the youngest leaf tips. However, when
boron is deficient, the breakdown occurs at the bases of the
youngest leaves. Death of the terminal growing points is the final
result in both cases. |
3. Tissue breakdown necrosis and
firing of the tip and margins of the leaf.
The ammonium cation in itself may become phytotoxic and result
in breakdown of the plant tissue (proteolysis -breakdown of
plant proteins) initially producing a wet, dark-green, "steamed"
appearance at the leaf tips and margins. This destroyed tissue
eventually desiccates and becomes a light tan color. Excess
ammonium may also induce calcium deficiency (abnormally dark
green foliage, scalloped leaf margins, weak stem structure,
death of terminal bud or growing point of the plant, premature
shedding of the blossoms and buds)... ammonium excess |
B. Terminal bud remaining alive. Symptoms on
new growth. |
1. Interveinal chlorosis on young leaves. |
a. Interveinal chlorosis on young leaves
with larger veins only remaining green. Necrotic spots
usually absent; however, with extreme deficiencies, young
leaves are almost white and may have necrotic margins and
tips; necrotic spots may extend inward. potassium,
zinc or copper excess can inhibit uptake of
iron. High pH may also induce iron deficiency....iron
deficiency |
Iron deficiency symptoms are similar to those of
magnesium deficiency, but iron deficiencies occur in young leaves
first: Iron accumulated in older leaves is relatively immobile in
the phloem. |
b. Interveinal chlorosis with smallest
veins remaining green producing a checkered or finely
netted effect. Grey or tan necrotic spots usually develop in
chlorotic areas; the dead spots of tissue may drop out of the
leaf giving a ragged appearance. Poor bloom-both size and
color. potassium excess can inhibit uptake of
manganese... manganese deficiency |
c. Stunted new growth with interveinal
chlorosis: Young leaves are very small ("little leaf"),
sometimes missing leaf blades altogether, and internodes are
short giving a rosette appearance... zinc deficiency |
2. Interveinal chlorosis is not the main
symptom on new growth. |
a. Wilting and loss of turgor of young,
terminal leaves and stem tips is common. Symptoms are
highly dependent upon plant species. In some species younger
leaves may show interveinal chlorosis while tips and lobes
of older leaves remain green followed by veinal chlorosis
and rapid, extensive necrosis of leaf blade... copper
deficiency |
There are no known reports of H2PO4-1 toxicity;
however, plants may take up the phosphate anion in luxury amounts.
Phosphorus excess is associated with impeded uptake and possible
deficiency of copper and sometimes of zinc... phosphorous
excess |
b. Leaves light green, veins lighter in color
than adjoining interveinal areas. Leaves over entire plant
may become yellowish green, roots and stems are small in
diameter and are hard and woody. Young leaves may appear to be
uniformly yellow. Some necrotic spots... sulphur
deficiency |
In plant species where the sulfur is not withdrawn
from the older leaves and retranslocated to the new growth, leaves
matured prior to onset of sulfur deficiency remain green: This
retention of green color of older foliage distinguishes sulfur
deficiency in these species from nitrogen deficiency where the
nitrogen is translocated from the older foliage into the new
leaves. With nitrogen starvation, old leaves as well as new leaves
turn yellow. |
c. Shoot inhibition causing malformed and
twisted tops with major injury at the tips and edges of the
leaves... xylem-translocated "shoot-inhibiting
chemicals" |
EXAMPLES OF TOXIC XYLEM-TRANSPORTED
CHEMICALS include the thiocarbamate herbicides (symptoms on
grasses and broadleaves) and alachlor and metolachlor (symptoms on
grasses) |
d. Young tissues discolored or deformed
and injury may persist for several sets of new leaves...toxic
phloem-translocated chemicals |
EXAMPLES OF TOXIC PHLOEM-TRANSPORTED
CHEMICALS include the herbicides 2, 4-D, dicamba, picloram,
glyphosate, amitrole, dalapon, sethoxydim and fluazifopbutyl. |
II. Symptoms do not appear first or most severely
on youngest leaves: Effect general on whole plant or localized
on older, lower leaves. |
A . Chlorosis general, no interveinal
chlorosis. Effects usually general on whole plant. |
1. Visible symptoms include yellowing and
dying of older leaves. Foliage light green, growth
stunted, stems slender, yellow...nitrogen deficiency |
Plants receiving enough nitrogen to attain limited
growth exhibit deficiency symptoms consisting of a general
chlorosis, especially in older leaves. In severe cases, these
leaves become completely yellow and then light tan as they die.
They frequently fall off the plant in the yellow or tan stage. |
2. Older leaves wilt. Entire leaf is
affected by chlorosis, but edges and leaf tissues near main
veins often retain more color (chlorophyll)...zinc
excess |
B. Vein-clearing, chlorosis-necrosis at leaf tips
and margins, older-younger foliage...xylem-transported
photosynthetic-inhibitors. When toxic chemicals are
xylem-translocated to older, fully-expanded leaves, the toxicity
symptoms generally occur on the margins and interveinal areas of
the leaf. When translocated to young, expanding leaves, toxicity
symptoms are generally associated with the veins, especially the
midrib. |
EXAMPLES OF XYLEM-TRANSLOCATED,
PHOTOSYNTHETIC INHIBITORS include the triazine, urea and uracil
herbicides. |
C. Interveinal chlorosis. Interveinal chlorosis
first appears on oldest leaves. |
1. Older leaves chlorotic, usually
necrotic in late stages. Chlorosis along leaf margins
extending between veins produces a "Christmas tree"
pattern. Veins normal green. Leaf margins may curl downward
or upward with puckering effect. Necrosis may suddenly occur
between veins. Potassium or calcium excess can
inhibit uptake of magnesium...magnesium deficiency |
When the external magnesium supply is deficient,
interveinal chlorosis of the older leaves is the first symptom
because as the magnesium of the chlorophyll is remobilized, the
mesophyll cells next to the vascular bundles retain chlorophyll
for longer periods than do the parenchyma cells between them.
Leaves lose green color at tips and between veins followed by
chlorosis or development of brilliant colors, starting with lower
leaves and proceeding upwards. The chlorosis/brilliant colors
(unmasking of other leaf pigments due to the lack of chlorophyll)
may start at the leaf margins or tips and progress inward
interveinally producing a "Christmas" tree pattern.
Leaves are abnormally thin, plants are brittle and branches have a
tendency to curve upward. Twigs are weak, subject to fungus
infection, usually leaves drop prematurely; plant may die the
following spring. |
2. Smaller veins in older leaves may turn
brown. Small necrotic spots in older leaves spread from
the margins inwards, and finally desiccate the entire leaf
blade. At severe, advanced stages, young leaves also display
this spotting... manganese excess |
3. Chlorotic areas (pale yellow) on
whole plant; leaf edges curl upward... molybdenum
deficiency |
General symptoms are similar to those of nitrogen
deficiency: Interveinal chlorosis occurring first on the older or
midstem leaves, then progressing to the youngest. Sometimes, as in
the "whiptail" disease, plants grown on ammonium
nitrogen may not become chlorotic, but develop severely
twisted young leaves, which eventually die. Other characteristic
molybdenum deficiency symptoms include marginal scorching and
rolling or cupping of leaves. With molybdenum deficiency, nitrogen
deficiency symptoms may developing the presence of adequate levels
off nitrate nitrogen in the root environment and high levels of
nitrate nitrogen in the plant. Nitrate nitrogen must be reduced in
the plant before it can be utilized. Molybdenum is required for
this reduction, and if molybdenum is deficient, nitrate may
accumulate to a high level in the plant, and at the same time the
plant may exhibit nitrogen deficiency symptoms. Molybdenum differs
from other trace nutrients in that many plants can develop in its
absence provided that ammonium nitrogen is present. Molybdenum
appears to be essential for the nitrate-reducing enzyme to
function. Molybdenum deficiencies are commonly found in
Northeastern Washington. |
4. Foliar marginal necrosis is the
most common symptom of fluoride toxicity along with Chlorosis
along and between the veins occurs in fluorine-sensitive plants.
With many plants, the marginal necrosis is preceded by the
appearance of gray or light-green, water-soaked lesions which
later turn tan or reddish-brown. Injury generally occurs at the
tips of the leaves first, then moves inward and downward until a
large part of the leaf is affected... fluoride excess |
D. Leaf chlorosis is not the dominant symptom.
Symptoms appear on older leaves at base of plant. |
1. Plant dark green |
a. At first, all leaves are dark green and
growth is stunted. Purple pigment often develops in older
leaves, particularly on the underside of the leaf along the
veins...Leaves drop early... phosphorous deficiency |
Phosphorus deficiency is not readily identified by
visual symptoms alone. Visual symptoms of phosphorus deficiency
are not always definite, but many phosphorus deficient plants
exhibit off-color green foliage with purple venation, especially
on the underside of leaves, and plants are stunted and remain
stunted even when fertilizers supplying potassium and nitrogen are
applied. Older leaves assume a purple-bronze color. Small growth,
especially root development; spindly growth with tips of older
leaves often dead. Phosphorus is phloem retranslocated from older
leaves to new growth. |
Aluminum appears to affect root growth in particular:
Root tips blacken, no longer lengthen, but become thickened.
Excess aluminum accumulation in roots reduces their capacity for
translocating phosphorus. Amelioration involves suppression of
aluminum activity, for example by liming to bring the mediums
pH above 5.5, and not by addition of phosphorus. The toxic amount
of aluminum in a soil will depend upon other soil properties such
as pH and phosphorus content and upon the plant grown. Media
amendments such as perlite may release toxic quantities of
aluminum if the media pH is extremely acid...aluminum excess |
b. Leaves are thick and brittle and deep green.
In acute toxicity, older leaves wilt and scorch from the
margins inward... nitrate excess |
2. Necrotic spots develop on older leaves |
a. Margins of older leaves become chlorotic
and then burn, or small chlorotic spots progressing to
necrosis appear scattered on old leaf blades. Calcium
excess impedes uptake of potassium cations.... potassium
deficiency |
Potassium deficiency symptoms first appear on the
recently matured leaves of the plant (not on the young, immature
leaves at the growing point). In some plants, the first sign of
potassium deficiency is a white specking or freckling of the leaf
blades. With time, the symptoms become more pronounced on the
older leaves , and they become mottled or yellowish between the
veins and scorched at the margins. These progress inward until the
entire leaf blade is scorched. If sodium cations are present and
taken up in place of K+1, leaf flecking (necrotic spots scattered
on leaf surface) and reduced growth occur. Seed or fruit is
shriveled. Potassium is phloem retranslocated from old leaves to
new growth. |
b. Tips and edges of leaves exhibit necrotic
spots coalescing into a marginal scorch. Symptoms
proceed from the plants base upwards with older leaves
being affected first. In advanced, severe toxicity, necrotic
spots with a pale brown center also appear in the inner parts
of the leaf blade... boron excess |
c. Mottling and necrotic spots primarily on
margin and interveinally may occur on leaves due to
excessive amounts of fertilizers or pesticides applied either
as foliar sprays... direct-contact of toxic chemical with
shoot & foliage |
EXAMPLES OF SHOOT DIRECT-CONTACT TOXIC
CHEMICALS INCLUDE the shoot-foliage applied herbicides paraquat,
acifluofen, dinoseb and the herbicidal oils produce this type of
symptom. |
3. Reduced growth and wilting of older leaves
with development of chlorotic and necrotic spots. Roots become
stunted in length and thickened, or club-shaped, near the tips:
The shoots remain normal but may show nutrient and moisture
stress. Under severe conditions, root tips may be killed causing
general stunting of the plant, wilting followed by marginal
drying of the lower leaves first... direct-contact injury by
toxic chemicals or other factors in the root zone, i.e. low
temperatures; nematodes; root weevils. |
EXAMPLES OF ROOT DIRECT-CONTACT TOXIC
CHEMICALS INCLUDE excess salts or presence of toxic chemical such
as the herbicides DCPA, dinitroanilines, diphenamid. |
Leaves eventually become bronze colored....chloride
deficiency |
4. Marginal scorching that may progress to
general leaf scorching. Generally no spotting... excess
salt or sodium excess |
5. Intense yellow or purple color in leaves.
Molybdenum excess or toxicity in field-grown plants is rarely
observed. Plants appear to tolerate relatively high tissue
concentrations of molybdenum. Isolated reports of symptoms from
excess molybdenum include development of intense yellow color in
tomato leaves and intense purple color in cauliflower leaves...
molybdenum excess |
References, Laboratory Analyses |
If you have identified the plant and have narrowed the
probable cause down through the various categories, (i.e.
distinguished between living and nonliving then if living,
distinguished between pathogens and animal factors then if
pathogen, distinguished between fungal and bacterial organisms),
you will probably need assistance in identifying the specific
responsible organism or nonliving factor. But, by now you know
what specialist to contact (plant pathologist, entomologist,
physiologist...) and what specific reference book would provide
further assistance in narrowing down the search for the specific
factor causing the observed plant damage. Laboratory analyses and
examination may be required to further narrow the range of
probable causes. |
V. Synthesis of Information to Determine Probable
Causes of the Plant Damage |
The detective work to find the "signs"
(residues of the living, damaging organism or nonliving factor,
records, etc.) is time consuming and methodical. But, without this
process of elimination and synthesis, probability of making a
correct diagnosis is low. |