Air Pollution Damage to Plants
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A L A B A M A A & M A N D A U B U R N U N I V E R S I T I E S
Air Pollution
ANR-913 Damage to Plants
T he annual losses of food
and fiber crops, ornamental
plants, turfgrasses, and trees
in the United States caused by air
pollution are estimated to be more
Other important factors are city
size and location, land topography,
soil moisture and nutrient supply,
maturity of plant tissues, time of
year, and species and variety of
than a billion dollars. Injury caused plants. A soil moisture deficit or
by air pollution is often evident on extremes of temperature, humidity,
plants before it can affect humans and light often alter a plant’s re-
or other animals. sponse to an air pollutant.
This publication discusses the Damage caused by air pollu-
more important pollutants, includ- Figure 1. Dark pigmented stipple on
upper surface of yellow poplar leaves
tion is usually most severe during
ing the inorganic pollutants—sulfur exposed to ozone. warm, clear, still, humid weather
dioxide, fluoride, chlorine, and when barometric pressure is
ozone—and the organic pollut- high. Toxicants accumulate near
ants—peroxyacetyl nitrate (PAN) Factors the earth’s surface when warm
and ethylene. It describes their
symptoms and the concentration Influencing Air air aloft traps cooler air at ground
level. This is called air inversion.
likely to cause plant injury. It also Pollution
lists plants that are very sensitive to
the pollutant and plants which are Injury to Plants Sulfur Dioxide
somewhat resistant. Plant injury caused by air pol- The exposure of succulent,
lution is most common near large broad-leaved plants to sulfur
dioxide (SO2) and its by-
Symptoms of cities, smelters, refineries, electric
power plants, airports, highways, product sulfuric acid usually
Air Pollution incinerators, refuse dumps, pulp results in dry, papery blotches
that are generally white, tan, or
Damage to Plants and paper mills, and coal-, gas-, or
petroleum-burning furnaces. Plant straw-colored and marginal or
The effects of pollution on injury also occurs near industries interveinal (Figure 2). On some
plants include mottled foliage, that produce brick, pottery, ce- species, chronic injury causes
“burning” at leaf tips or margins, ment, aluminum, copper, nickel, brown to reddish brown or black
twig dieback, stunted growth, iron or steel, zinc, acids, ceramics, blotches (Figure 3). Both the
premature leaf drop, delayed ma- glass, phosphate fertilizers, paints upper and lower leaf surfaces are
turity, abortion or early drop of and stains, rubbers, soaps and affected. The leaf veins normally
blossoms, and reduced yield or detergents, and other chemicals. remain green. Chlorosis (yellow-
quality (Figure 1). In general, the Damage in isolated areas occurs ing) and a gradual bleaching of
visible injury to plants is of three when pollutants are spread long the surrounding tissues is fairly
types: (1) collapse of leaf tissue distances by wind currents. common. Injured grass blades
with the development of necrotic develop light tan to white streaks
Factors that govern the extent
patterns, (2) yellowing or other on either side of the midvein. A
of damage and the region where
color changes, and (3) alterations tan to reddish brown dieback or
air pollution is a problem are
in growth or premature loss of banding occurs on conifer leaves,
(1) type and concentration of
foliage. Injury from air pollution with adjacent chlorotic areas.
pollutants, (2) distance from the
can be confused with the symp- Growth suppression, reduction in
source, (3) length of exposure,
toms caused by fungi, bacteria, yield, and heavy defoliation may
and (4) meteorological conditions.
viruses, nematodes, insects, nutri- also occur. Middle-aged leaves
For some pollutants, damage can
tional deficiencies and toxicities, and young plants are most sus-
occur at levels below Environmental
and the adverse effects of tem- ceptible to sulfur dioxide.
Protection Agency standards.
perature, wind, and water.
www.aces.edu
barley, bean (broad and garden), grasses and conifers (Figures 4
beech, beet (table and sugar), and 5). A narrow, chlorotic to
begonia, bindweed, birch, black- dark brown band often occurs
berry, bluegrass (annual), broc- between living and dead tissue.
coli, bromegrass, brussels sprout, Citrus, poplar, sweet cherry, and
buckwheat, carrot, catalpa, cen- corn foliage exhibit a chlorotic
taurea, chickweed, China aster, mottling, streaking, or blotching
clovers, columbine, cosmos, prior to the development of the
cotton, crabapple, curly dock, typical “burned” area. On apple,
dahlia, dandelion, Douglas fir, apricot, citrus, fig, peach, plum,
Figure 2. Marginal and interveinal eggplant, elm, endive, fir (white), and prune, leaves and fruit may
necrosis on American beech leaves ex-
fleabane, forsythia, four o’clock, fall prematurely. Injured areas in
posed to sulfur dioxide.
hawthorn (scarlet), larch, let- stone fruit leaves may become
tuce (garden and prickly), mal- brittle and drop out, leaving shot-
low, morning glory, mulberry, holes. Young, succulent growth
mustard, oat, okra, orchardgrass, is injured the easiest. Fruit may
Pacific ninebark, peach, pear, soften or become necrotic at the
pecan, pepper (bell and chili), blossom end. Fluoride-contami-
petunia, pine (Austrian, jack, nated forage that is eaten by cat-
loblolly, ponderosa, Virginia, tle or sheep may cause fluorosis.
white), plantain, polygonum, Fluorides are produced by
poplar, pumpkin, quince, rad- glass, aluminum, pottery, brick,
ish, ragweed, raspberry, rhubarb, and ceramic industries and by
Figure 3. Dark, reddish pigmentation rockspirea, rose, rye, ryegrass, refineries, metal ore smelters, and
on dogwood leaves exposed to sulfur safflower, saltbush, smartweed, phosphate fertilizer factories.
dioxide. soybean, spinach, spruce, squash,
strawberry, sumac, sunflower,
Sulfur dioxide injury can be sweet pea, sweet potato, Swiss
severe 30 miles or more from its chard, tomato, tulip tree, turnip,
source. Injury, however, is usually velvetweed, verbena, violet,
greatest in the vicinity of the source wheat, and zinnia.
(less than 1 to 5 miles away).
Sources of sulfur dioxide include Somewhat
electric power plants, copper and Resistant Plants
iron smelters, oil refineries, chemi- Arborvitae, box elder, canna,
cal factories, and other industries castor bean, celery, chrysanthe-
that burn soft coal, coke, or high- mum, citrus, corn, cucumber,
sulfur oil as fuel. ginkgo, gladiolus, gourds, hibis-
Figure 4. Yellowish mottle and margin-
cus, honeysuckle, horseradish,
Concentration iris, Johnsongrass, lilac, maple,
al chlorosis on sweetgum leaf exposed
to fluorides.
The degree of injury increases milkweed, mock orange, musk-
as both the concentration of sulfur melon, most oaks, onion, po-
dioxide and the length of expo- tato, privet, purslane, shepherd’s
sure increase. Sensitive plants are purse, snowball, sorghum, tulip,
injured by exposures of 0.5 parts viburnum, Virginia creeper, wil-
per million (ppm) for 4 hours, or low, and wisteria.
0.25 ppm for 8 to 24 hours. Plants
are most sensitive to sulfur diox-
ide during periods of bright sun,
Fluorides
high relative humidity, and ad- Fluorides are compounds con-
equate plant moisture during the taining the element fluorine (F).
late spring and early summer. The typical injury by gaseous or
particulate fluorides is either a Figure 5. Tip necrosis on needles of
eastern white pine exposed to fluo-
Very Sensitive Plants yellowish mottle to a wavy, red- rides.
dish brown or tan “scorching”
Alfalfa, amaranthus, apple, at the margin and tips of broad-
apricot, ash (green and white), leaved plants or a “tipburn” of
aspen, aster, bachelor’s button,
2
Concentration cust, marigold, mountain ash Very Sensitive Plants
(European), nightshade, onion,
Accumulated leaf-fluoride Alfalfa, amaranthus, apple, ash,
orchardgrass, parsnip, pear, pep-
concentrations of 20 to 150 ppm azalea, barberry, basswood, bean
per, petunia, pigweed, planetree,
often injure sensitive plants, al- (Pinto and Scotia), birch (gray),
plum (flowering), plantain, privet,
though resistant varieties and blackberry, bluegrass (annual),
purslane, pyracantha, ragweed,
species of plants will tolerate box elder, bridal wreath,
rhododendron, rose, snapdragon,
leaf concentrations of 500 to buckwheat, catbrier, cherry,
soybean, spinach, squash, spruce
4,000 ppm or more without vis- chickweed, chokecherry, coleus,
(Engelmann), strawberry, sweet
ible injury. A 4-week exposure cosmos, cucumber, dandelion,
pea, tobacco, tomato, tree-of-
of susceptible gladiolus to an air dogwood, gomphrena, grape,
heaven, Virginia creeper, willow
concentration of 0.0001 ppm, or honeysuckle, horse chestnut,
(weeping), wheat, and zinnia.
less than 24 hours at 10 parts per hydrangea, Johnsongrass, Johnny-
billion, produced leaf concentra- jump-up, juniper, lilac, mallow,
tions of 150 ppm and definite Chlorine maple (Norway, silver, sugar),
tissue necrosis. Susceptibility to Injury caused by chlorine May apple, morning glory,
fluorides varies tremendously (Cl2) is somewhat similar to that mulberry, mustard, oak (pin),
among varieties or clones of caused by sulfur dioxide and onion, peach, peony, petunia,
the same plant, such as apricot, fluorides, in that it is marginal phlox, pine (jack, loblolly,
begonia, corn, gladiolus, grape, and interveinal. On broad-leaved shortleaf, slash, white), poison
peach, ponderosa and white plants, necrotic, bleached, or tan ivy, primrose, privet, radish, rose
pines, and sweet potato. The ex- to brown areas tend to be near (tea), sassafras, spruce (Norway),
tent of tissue damage is related the leaf margins, tips, and be- sunflower, sweetgum, tomato,
to the dosage and the quantity of tween the principal veins. Injured tree-of-heaven, tulip, Venus’s
fluoride accumulated. grass blades develop progressive looking-glass, violet, Virginia
streaking toward the main vein creeper, witch hazel, and zinnia.
Very Sensitive Plants in the region between the tip and
Alfalfa, apple, apricot (Chinese, the point where the grass blade Somewhat
Moorpark, Royal, Tilton), aza- bends. The streaking usually oc- Resistant Plants
lea, barley, blueberry, box elder, curs alongside the veins. Middle- Arborvitae, begonia, ivy
buckwheat, canna, cattail, cherry, aged leaves or older ones are (Boston), day lily, eggplant, hem-
chickweed, citrus, corn (sweet), often more susceptible than the lock, holly (Chinese), iris, lamb’s-
crabgrass, cyclamen, Douglas fir, young ones. Bleaching and tis- quarters, maple (Japanese), oak
gladiolus, grape (European), hy- sue collapse can occur. Conifers (red), oxalis, pepper, pigweed,
pericum, iris, Jerusalem cherry, may show tipburn on the current polygonum, Russian olive, soy-
Johnsongrass, larch (western), season’s needles. bean, and yew.
mahonia, maple, mulberry, nettle- Hydrogen chloride and chlo-
rine are emitted from the stacks
leaf goosefoot, some oaks, oxalis,
peach, peony, most pines, plum, of glassmaking factories and
Ozone
poplar, prune (Italian), smart- refineries. These gases are also Ozone (O3) is probably the
weed, sorghum, spruce (blue and produced by incineration, scrap most important plant-toxic air
white), sweet potato, and tulip. burning, and spillage, such as pollutant in the United States. It
from chlorine storage tanks. is a very active form of oxygen
Somewhat Chlorine-injured vegetation is that causes a variety of symptoms
Resistant Plants often observed near swimming on broad-leaved plants: tissue
pools, water-purification plants, collapse, interveinal necrosis,
Ash (European and Modesto), and markings on the upper sur-
and sewage-disposal facilities.
asparagus, bean, birch (cutleaf), face of leaves known as stipple
bridal wreath, burdock, Canter-
bury bell, cauliflower, celery,
Concentration (pigmented yellow, light tan,
red brown, dark brown, red,
cherry (flowering), chrysanthe- Very susceptible plants show
black, or purple), flecking (sil-
mum, citrus, columbine, cotton, symptoms when exposed for 2
ver or bleached straw white),
cucumber, currant, dandelion, hours or more at concentrations
mottling, chlorosis or bronzing,
dock, dogwood, eggplant, elder- of chlorine ranging from 0.1 to
and bleaching (Figures 6 and 7).
berry, elm (American), fir (grand), 4.67 ppm. Chlorides do not accu-
Ozone stunts plant growth and
galinsoga, hemlock, most juni- mulate in plant tissues after expo-
depresses flowering and bud for-
pers, laurel, lettuce (Romaine), sure to chlorine.
mation. It also causes marginal
linden (American), lobelia, lo- rolling and scorching of leaves
3
on lilac. Affected leaves of certain carrot, catalpa, celery, chicory,
plants, such as citrus, grape, and chickweed, Chinese cabbage,
tobacco, commonly wither and chrysanthemum, citrus, clover
drop early. (red), corn (sweet), crabapple,
Conifers frequently show a crabgrass, dahlia, dill, duckweed,
yellow to brown mottling and eggplant, endive, fuchsia, gourds,
tipburn, or a yellow to brown or grape, hemlock, honeylocust,
orange-red flecking and band- hypericum, larch (European),
ing of the needles (Figure 8). lilac, linden, locust (black), maple
Susceptible white pines are stunt- (silver and sugar), marigold,
Figure 6. Bronzing of lower surface of
ed or dwarfed and chlorotic. The potato leaf exposed to ozone.
mint, mimosa, muskmelon, oak
injury pattern in small grains and (gambel and white), oat, onion,
forage grasses generally occurs as orchardgrass, parsley, parsnip,
a scattering of small, yellowish or pea, peach, peanut petunia, pine
white to tan flecks on one or both (ponderosa, scotch, white), po-
leaf surfaces. The flecks may later tato, privet, pumpkin, radish, rye,
merge to form larger, bleached salvia, scallion, smartweed, snow-
white to yellowish dead areas. berry, spinach, squash, straw-
Ozone usually attacks nearly ma- berry, sweet potato, Swiss chard,
ture leaves first, progressing to sycamore, tobacco, tomato, tulip
younger and older leaves. Young tree, turnip, verbena, walnut,
plants are generally the most wheat, and willow (weeping).
sensitive to ozone; mature plants, Figure 7. Bleaching of upper surface of
relatively resistant. Ozone-killed watermelon leaves exposed to ozone. Somewhat
tissues are readily infected by cer- Resistant Plants
tain fungi, such as Botrytis. Coleus, cotton, cucumber,
Ozone is brought down from dogwood, euonymus, geranium,
the stratosphere by vertical winds gladiolus, impatiens, juniper
or produced during electrical (Pfitzer), kalanchoe, most maples,
storms; more importantly, it is most oaks, pepper, poinsettia,
produced when sunlight reacts tolmiea, and yew.
with nitrogen oxides and hydro-
carbons formed by refuse burn-
ing and combustion of coal or
Peroxyacetyl
petroleum fuels, especially the
Figure 8. Tipburn on eastern white
Nitrate (PAN)
exhaust gases from internal- The most plant-toxic oxidant,
pine exposed to ozone.
combustion engines. When oxi- next to ozone, is PAN. PAN
dant levels in the air are high, causes a collapse of tissue on the
more than 90 percent is ozone. spinach, squash, sweet corn, and
tobacco. The extent of the injury lower leaf surface of numerous
These levels are usually at their plants. The typical leaf marking
highest point in the afternoon depends on the plant species and
environmental conditions prior to is a glazing, bronzing, or silver-
and relatively low at night. ing that commonly develops
and during exposure. Ozone and
sulfur dioxide often combine to in bands or blotches. On some
Concentration plants, such as petunia, Pinto
cause plant injury before either
The exposure of sensitive of these pollutants alone would bean, tomato, and tobacco, the
plants for 4 hours at levels of cause damage. collapse may be through the en-
0.04 to under 1.0 ppm of ozone tire thickness of the leaf blade.
will produce injury patterns. Very Sensitive Plants In grasses, the collapsed tissue
Susceptible tobacco plants are has a bleached appearance, with
injured when concentrations Abutilon, alder, alfalfa, apricot, tan to yellow, transverse bands.
of ozone reach or exceed 0.04 ash (green and white), aspen, Conifer needles turn yellow. Early
ppm. (Ozone injury on tobacco aster, avocado, barley, bean maturity or senescence, chloro-
is called weather fleck.) Ozone (green and Pinto), beet (table and sis, moderate to severe stunting,
susceptibility differs greatly be- sugar), begonia, bentgrass, birch, and premature leaf drop may
tween varieties of the same plant, bluegrass (annual), box elder, also occur. PAN is most toxic to
for example, bean, grape, oat, bridal wreath, broccoli, brome- small plants and young leaves.
onion, petunia, pine, potato, grass, brussels sprout, carnation,
4
The very young and most mature Somewhat Concentration
leaves are highly resistant. Resistant Plants Air concentrations of 0.001
Like ozone, PAN is produced ppm for 24 hours will cause
Azalea, bean (lima), begonia,
when sunlight reacts with various the sepals of orchid flowers to
broccoli, cabbage, chrysanthe-
exhaust gases. PAN is formed by turn brown or wither and die.
mum, corn, cotton, cucumber,
oxides of nitrogen reacting with An exposure of 0.1 ppm for 6
onion, pansy, periwinkle, rad-
unsaturated hydrocarbons (simple hours will cause epinasty in to-
ish, redwood, sequoia, sorghum,
olefins) in the presence of light. mato or pepper and sleepiness
touch-me-not, and wheat.
Other PANs, such as peroxypro- in carnation. The extent of injury
pionyl nitrate and peroxybutyryl
nitrate, may also be present in Ethylene depends on the air temperature,
plant species, and age of the
urban air and may produce Damage caused by ethylene organ, as well as on the ethylene
symptoms that are indistinguish- (H2C-CH2) is often associated concentration.
able from those caused by per- with PAN and ozone in urban
oxyacetyl nitrate. areas. Ethylene modifies the ac- Very Sensitive Plants
tivities of plant hormones and
Concentration Azalea, bean (Black Valentine),
growth regulators, which affect
blackberry, buckwheat, calceo-
Typical damage to susceptible developing tissues and normal
laria, carnation, cotton, cowpea,
plants occurs with PAN at levels organ development, without
cucumber, larkspur, lilac, lily
of 0.01 to 0.05 ppm for an hour causing leaf-tissue collapse and
(Regal), marigold (African), nar-
or more. Plant injury requires necrosis. Injury to broad-leaved
cissus, orchid, pea, peach, pep-
light before, during, and after ex- plants occurs as a downward
per, philodendron, potato, privet,
posure. Injury is increased by any curling of the leaves and shoots
roses, snapdragon, stock, sun-
factor contributing to maximum (epinasty), followed by a stunt-
flower, sweet pea, sweet potato,
plant growth. PAN is best known ing of growth. Ethylene also
tomato, and tulip.
in the Los Angeles basin area, causes dry sepal in Cattleya,
with injury occurring on vegeta- Phalaenopsis, and other orchids;
“sleepiness” (an inward petal-
Somewhat
tion from Seattle to San Diego.
Little is known about the concen- curling and failure of buds to Resistant Plants
tration of PAN in the Midwest or open) in carnation, narcissus, and Beet, cabbage, clover, endive,
the eastern United States. PAN is rose; color-breaking and blasted lettuce, oat, onion, radish, rye-
unstable, particularly at tempera- buds in roses; and the shelling grass, and sorghum.
tures above 90°F. (early drop) of azalea, snap-
dragon, stock, larkspur, and cal- Conclusion
Very Sensitive Plants ceolaria blooms. More-resistant,
Plant responses to air pollution
broad-leaved plants and grasses
African violet, alfalfa, aster, are helpful in the following ways:
may only be stunted. Conifers
bean (Pinto), beet (table and • Establishing the early pres-
drop their needles and young
sugar), bluegrass (annual), carna- ence of air-borne contaminants.
cones. New needle growth is
tion, celery, chickweed, dahlia,
stunted, and cone development • Determining the geographi-
dandelion, dill, Douglas fir, en-
is poor. Similar symptoms are cal distribution of the pollutants.
dive, escarole, fennel, lettuce
produced by other unsaturated • Estimating the concentration
(Romaine), lilac, muskmelon,
hydrocarbons such as acetylene of pollutants.
mustard, nettle (little-leaf), oat,
and propylene. • Providing a passive system
certain orchids, pepper, petunia,
pine (Coulter, Jeffrey, Monterey, Ethylene is one of the many for collecting pollutants for chem-
ponderosa), poinsettia, potato, products of auto, truck, and bus ical analyses later.
primrose, rose, salvia, snap- exhaust. Ethylene also results • Obtaining direct identifica-
dragon, spinach, sunflower, Swiss from the incomplete combustion tion of different air pollutants on
chard, tobacco, and tomato. of coal, gas, and oil for heating the basis of plant species and
and is a by-product of polyeth- variety affected.
ylene manufacture. Ethylene is a
problem in fruit, vegetable, and
cut-flower storage rooms and
greenhouses where manufactured
gas is still used.
5
Edward J. Sikora, Extension Plant Pathologist, Professor, Entomology
and Plant Pathology; and Arthur H. Chappelka, Professor, Forestry and
Wildlife Sciences, both at Auburn University
Source for figures 1-5 and 8: Shelley, John M., et al., eds. 1987.
Diagnosing Injury To Eastern Forest Trees. USDA—Forest Service, Atlanta,
GA and The Pennsylvania State University, University Park, PA.
For more information, call your county Extension office. Look in your
telephone directory under your county’s name to find the number.
ANR-913 Issued in furtherance of Cooperative Extension work in agriculture and home economics, Acts of May 8 and June
30, 1914, and other related acts, in cooperation with the U.S. Department of Agriculture. The Alabama Cooperative
Extension System (Auburn University and Alabama A&M University) offers educational programs, materials, and equal
opportunity employment to all people without regard to race, color, national origin, religion, sex, age, veteran status,
or disability. 4M, Reprinted Dec 2004, ANR-913
© 2004 by the Alabama Cooperative Extension System. All rights reserved.
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