Control PLANT DISEASES
For Better Farming And Better Living

Mimeo BP 2-3
March, 1959

CHLOROSIS OF TREES AND SHRUBS
Chlorosis or yellowing of the leaves of shade trees and ornamen-
tal shrubs is a condition that may occur on individual plants in any
season.
“Chlorotic” or yellowed trees of shrubs may show complete or
partial yellowing of the leaves. The yellow condition first occurs
between the veins leaving a network of green veins on a very light-
green background. In severe cases the leaves may become almost
white, even drying up and falling from the plant. Sometimes the
tips of affected branches may die, especially in the tops of the
trees. Some affected trees may have dead tops while the lower limbs
still have almost normal foliage. Severe stunting, poor root devel-
opment and eventual death may result from chlorosis.
What Causes Chlorosis
Chlorosis may be caused by several factors but lack of available
iron is the most frequent cause. Iron is necessary for the formation
of chlorophyll which is the substance responsible for the green color
in plants. When iron is deficient in the soil or is not available to
the plant, chlorosis results. When there is an excess of lime in the
soil (pH 6.7-8.5) it interfers with the availability of iron to the
plant, even when there is a considerable amount of iron in the soil.
This failure of the plant to receive a normal iron supply results in
the leaves not forming a sufficient amount of the green pigment known
as chlorophyll.
High temperatures and high light intensities usually accentuate
chlorosis.
What Plants are Susceptible to Chlorosis
Several types of shade trees are very sensitive to iron defici-
ency. Pin oak, catalpa, white maple, sycamore, cottonwood, willow
and black locust are very susceptible to yellowing as a result of
iron deficiency. Honey locust, Ailanthus, Russian olive, Red cedar,
Chinese elm, and Austrian pine seldom show symptoms of chlorosis.
Certain plants such as spirea, privet, rose, iris, peony, wild plum,
peach, pear, cherry and grapes are also quite susceptible to iron
chlorosis.
How to Correct Chlorosis
There are three ways in which chlorosis may be corrected by
treating affected plants with iron salts. These are l) soil ap-
plications 2) foliar sprays and 3) injections.

PURDUE UNIVERSITY Agricultural Extension Service, Lafayette, Indiana
Department of Botany and Plant Pathology, Life Science Building