Chlorosis of Landscape Plants
Chlorosis is a yellowing of leaf tissue
due to a lack of chlorophyll. Possible causes of chlorosis include
poor drainage, damaged roots, compacted roots, high alkalinity, and
nutrient deficiencies in the plant. Nutrient deficiencies may occur
because there is an insufficient amount in the soil or because the
nutrients are unavailable due to a high pH (alkaline soil). Or the
nutrients may not be absorbed due to injured roots or poor root growth.
The lack of iron is one of the more common nutrients associated
with chlorosis. Manganese or zinc deficiencies in the plant will
also cause chlorosis. The way to separate an iron deficiency from
a zinc or manganese deficiency is to check what foliage turned chlorotic
first. Iron chlorosis starts on the younger or terminal leaves and
later works inward to the older leaves. However, manganese and zinc
deficiencies develop on the inner or the older leaves first and
then progress outward.
Plants need iron for the formation of chlorophyll. Chlorophyll
gives leaves their green color and is necessary for the plant to
produce the food it needs for its own growth. Iron is also necessary
for many enzyme functions that manage plant metabolism and respiration.
Iron becomes more insoluble as the soil pH climbs above 6.5 to 6.7
(7.0 is neutral - below 7.0, the pH is acidic; above 7.0, the pH
is alkaline). With most plants, iron can only be absorbed as a free
ion (Fe++) when the pH is between 5.0 and 6.5.
Other elements such as calcium, zinc, manganese, phosphorus, or
copper in high amounts in the soil can tie up iron so that it is
unavailable to the plant. However, a shortage of potassium in the
plant will reduce the availability of iron to the plant. Insufficient
iron in the soil is also a problem. In the Chicagoland area, most
soils have adequate iron. The problem is the availability of the
iron in soil to the plant. In Northeastern Illinois, most soils
were formed from limestone bedrock. Thus the chlorosis problem is
often due to high soil pH.
Herbaceous plants as well as woody plants are susceptible to chlorosis.
Symptoms can vary depending on several factors. How alkaline is
the soil? The higher the pH, the more chlorotic the plant. How long
has the plant been chlorotic? In general, the longer the plant has
been chlorotic, the more severe the chlorosis. Generally, mild chlorosis
starts as a paling (lighter green to lime-green color) of interveinal
(between veins) tissue, whereas a yellow color indicates a more
serious condition. In some cases, only part of the plant is chlorotic.
Affected areas (or the entire plant) may be stunted or fail to produce
flowers and fruit. In addition, chlorotic leaves are more prone
to scorching and leaf diseases. With severe chlorosis, the leaf
veins will turn yellow, followed by the death of the leaf, the affected
branch may die back, and death of the entire plant can occur.
Treatment for chlorosis varies with the cause. If the chlorosis
is due to soil compaction, poor drainage, poor root growth or root
injury, then core aerification, tiling, mulching or some other cultural
practice may be needed. Nutrient deficiencies can be treated in
one of several ways.
Foliar applications of nutrients in a water soluble or chelate
form can correct the problem for awhile, but only affects the leaves
that are present during application. Leaves that develop and grow
after the treatment are not affected by the treatment. Therefore,
several treatments per growing season may be necessary to keep the
Another method is trunk application. Trunk application is quick
and may last several years. However, you should allow up to thirty
days for the tree to respond to trunk applications. There are a
couple of ways to apply nutrients via the trunk. Both methods involve
drilling holes in the trunk - the number of holes is based on trunk
diameter. With the first type of application, containers with tubes
are then attached to the holes. The tree's movement of moisture
will help draw the nutrients into the trunk. After the containers
are empty, they are removed and the holes are plugged. The other
method requires plastic capsules to be hammered into the drilled
holes. These capsules are designed to be left in the tree. In both
cases, consider hiring a professional to do trunk applications.
The final method for treating chlorosis is via soil treatment.
Soil tests should be taken to determine soil pH as well availability
of nutrients that can cause chlorosis. Based on a soil test, the
pH is corrected or the nutrients are applied by drilling holes in
the ground at a forty-five degree angle to a depth of twelve inches
starting three to five feet from the trunk and going as far out
as the tree is tall or property lines, foundation, streets, and
June - July 2000: Gardening
with Hebs - Part 2 | Chlorosis of Landscape Plants | Looking
Ahead to White Grub Control