Insect
and Disease Fact Sheet Compliments of New Century
1-877-79TREES
Iron Chlorosis
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Iron
is necessary for the formation of chlorophyll, which is responsible for the,
green color in plants and is the source of plant food and energy. When the
amount of iron, available to plants is inadequate for normal growth, leaves
become pale green, yellow or white and eventually brown, particularly between
the veins. Mildly affected plants become unsightly and grow poorly. Severely
affected plants fail to grow flower or fruit and may even die from lack of
iron. Iron
chlorosis occurs most often in pin oak, white oak,
white pine, magnolia, holly, sweet gum, dogwood, azalea and rhododendron. Iron
chlorosis may occur as a result of one or a
combination of causes. The condition is often due to high pH, which makes it
possible for other elements to interfere with the absorption of iron, rather
than a lack of iron in, the soil. This occurs in neutral to alkaline soils
when the pH is above 6.5 Clorosis may be caused by an actual deficiency of iron or by
applications of excessive amounts of lime or phosphate to certain soils. It may be caused by over-watering, poor
drainage or high levels of certain mineral elements in the soil such as manganese, copper or zinc. The
visual symptoms are often confused with other conditions such as a deficiency
of magnesium, manganese or boron, or possibly other non-nutrient related
problems. |
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Control
If
over watering or poor drainage are possible causes, they should be corrected.
Poor drainage is quite common in much of the silt and clay loam soils in Ohio,
and. tile lines may have to be installed near valuable trees.
The
pH, particularly in central and western Ohio, is quite often above 7. For permanent control, this must be lowered
by annually applying to the soil ammonium sulfate, aluminum sulfate or sulfur.
Ammonium sulfate is used at the rate of 10 pounds per 1,000 square feet and
sulfur at 25 pounds per 1,000 square feet per pH unit to be lowered and
aluminum sulfate at-higher rates.
A
soil sample and leaf sample should be taken and forwarded to the REAL
Laboratory at OARDC. The reports that are returned will give soil pH reading
and levels of as many elements as the sender specifies. This will reveal if
elements are deficient or in excess and, therefore, interfering with iron
uptake.
Once
these other possible causes have been corrected, applications of iron may not
be needed. If, however, plants remain chlorotic, iron
can be supplied to plants in different forms.
The
two principal types of iron-containing materials are iron chelates,
organic in nature, and inorganic compounds in soluble form such as ferrous
sulfate. Iron chelates are marketed under various trade
names and in various formulations. The iron in chelates
remains available to plants when the chelates are
placed in the soil. Some formulations of iron chelate
can be applied to the foliage; however, this approach is usually not as
permanent as soil applications. Follow the manufacturer's recommendations for
amount of use. Some fertilizers contain iron chelates,
and use of these with plants susceptible to iron deficiency is recommended.
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Ferrous sulfate can also be applied to the soil
or foliage. For foliar application, use 2 1/2 ounces of ferrous sulfate in 3
gallons of water. This treatment will probably require reapplication a number
of times. A convenient way to determine how much ferrous sulfate is needed
for soil application is to measure the diameter of the periphery of the tree
at the drip line (ends of branches). If the treatment is made when the trees
or shrubs are dormant, use 1 gallon of ferrous sulfate solution (1 pound of
ferrous sulfate per gallon of water) for each foot of the diameter of the
periphery. If the treatment is made
during the growing season, use 1/2 gallon per foot diameter. The solution can
be applied over the surface of the soil; however, it's more effective if
holes are drilled and the solution poured in. Drill holes 3 feet apart around
the periphery and deep enough to hold 1/2 to 1 gallon of solution. Injections
of liquid iron sulfate into tree trunks under pressure have also been
effective for one to two seasons. |
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Encapsulated ferric ammonium citrate inserted
into pin oak trees around the base of the trunk will prevent iron chlorosis for up to three years and is usually more
effective than either foliar or soil treatment. The small wounds caused by
drilling and capsule insertion should close in one season. |
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Generally, trees that are chlorotic
from a lack of iron will respond to one of the above treatments. Some plants
may require a combination of above treatments for two or more years to
completely cure the problem. |
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Information obtained through the Ohio State Extension Factsheet HYG-I009-88
Insect
and Disease Fact Sheet Compliments of New Century
1-877-79TREES