Control PLANT DISEASES
in yard and garden

BP-2-3
August 1973

Chlorosis of Trees, Shrubs and Ornamentals

Donald H. Scott
Extension Plant Pathologist

Chlorosis, a yellowing of leaves, occurs
on several trees, shrubs and ornamentals
commonly grown in Indiana. It results when
chlorophyll (green coloring matter) fails to
develop normally or is destroyed. Chloro-
sis is frequently caused by a lack of iron
which is necessary for the formation of
chlorophyll. Yellowing, induced by an iron
deficiency is known as "iron chlorosis."
Certain soils may be deficient in iron, but
more frequently the iron is "tied-up" and
unavailable for plant use when soil pH is
too high. Yellow foliage also may be caused
by extreme temperatures, poor drainage,
root damage, improper light, attack by fungi,
insects or viruses as well as an excess or
deficiency of soil nutrients such as magne-
sium, manganese, zinc, calcium, sulfur,
boron or nitrogen.
Iron chlorosis is most common when
plants are grown in soils containing lime-
stone, ashes or other alkaline materials
that increase the soil pH to 6. 7 to 8. 5. High
soil pH is frequently found in residential
areas next to brick, stucco or concrete
foundations, next to concrete sidewalks and
drives, where high-lime subsoils from
basement excavations were used as fill,
where excessive amounts of limestone were
applied, or where alkaline fertilizers or
hard water were used in lawn maintenance
for prolonged periods of time.

SYMPTOMS
The first symptom of iron chlorosis in
deciduous (leaf-shedding) plants is a uniform
blanching or yellowing of leaf tissues be-
tween the veins. The veins often appear
very green in contrast to surrounding tissue.
As iron deficiency becomes more pro-
nounced, the interveinal tissues become pro-
gressively lighter in color. In severe cases,
interveinal tissue may turn light to dark
brown and die. Premature defoliation may
occur. Entire terminals may die if the con-
dition is left uncorrected. Continued iron
deficiency may lead to severe stunting, poor
root development and even death of the en-
tire plant.
In conifers, needles first turn yellow.
Where severe, needles progressively turn
brown and die.
Occasionally, only a part of the plant
will show symptoms.
SUSCEPTIBLE PLANTS
Some plant species are more suscepti-
ble to iron chlorosis than others. In Indi-
ana, pin oak is one of the most sensitive.
Other trees likely to show iron chlorosis
symptoms include black locust, box elder,
bur and white oak, maple, pine, spruce,

COOPERATIVE EXTENSION SERVICE, PURDUE UNIVERSITY, WEST LAFAYETTE, INDIANA
Department of Botany and Plant Pathology, Life Seienee Building