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Affected leaves turn a yellowish
pale color while the leaf veins remain dark green. In
severe cases the leaf color may change from yellow to
white or brown. Iron deficiency or iron chlorosis is
the result in a loss of green color and the tree’s
inability to absorb the iron
it needs, for the production of chlorophyll. Symptoms
may appear over the entire tree, one side or limited
to individual branches. If iron chlorosis goes
untreated twigs and eventually branches may die
back leading to mortality of the tree.
 Texas
soils usually have adequate amounts of mineral iron.
However our soils contain usually high amounts of
phosphor and potassium and with the high pH
(alkalinity), this acts
as an iron blocker, changing the iron to insoluble
that trees are unable to absorb.
There are three methods of treatment to provide iron
to the trees: Foliar application, soil treatment and
trunk implantation.
Foliar Application:
If immediate response is needed to correct a
chloriotic condition, a foliar Spray with iron sulfate
or iron chelate solution should be applied when the
tree is in full leaf. A rate of five pounds of iron
sulfate in 100 gallons of water ( approx. 3 oz in
three gallons of water) is recommended. Soybean flour
may be added to help it adhere to the leaves or you
can use a surfactant according to label rates. Iron
chelates are water-soluble forms and remain in the
solution when added soil or tree. Always follow the
label instructions for determining the proper
concentration when applying chelated iron directly to
foliage. Is usually best to apply either iron sulfate
or iron chelate during the evening or during cool
weather periods. A foliar spray produces quick
results, or so to say a quick fix, the improvement is
temporary because iron will not move into the tree
beyond the tissue that was sprayed. New growth will
remain chlorotic after the treatment.
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Soil Treatment:
Lowering the soil pH is a
more permanent way of correcting iron chlorosis.
However, it is the most difficult treatment method
as it is almost impossible to lower the soil pH
sufficiently to depths of 18-24 inches. It is
recommended to apply iron sulfate at the rate of
1/2 pound per diameter inch at breast height, and
applied to, injection holes under the tree’s
canopy on a two foot square grid. Soil injection
using chelated iron may also be used at the
recommended label rates with liquid or wetable
sulfur at equal ratio amounts. This method
provides the soluble iron
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and the sulfur lowers the
pH in small areas and also helps make the
existing iron available.
mixture of equal
parts of iron (ferrous) sulfate and sulfur to
the soil.
Tree
Diameter
(inches) |
Total
amount of
Iron sulfate and
sulfur per tree
(pounds) |
Number of
holes
in ground around
tree |
Total
amount of equal
parts of ferrous
sulfate and sulfur per
hole (pounds)* |
| 1
|
1
|
4
|
0.25
|
| 2
|
2
|
8
|
0.25 |
| 3
|
3
|
12 |
0.25 |
| 4
|
6
|
12 |
0.5 |
| 5
|
10 |
20 |
0.5 |
| 6
|
12 |
24 |
0.5
|
| 7
|
14 to 18 |
19 to 36 |
0.5 to 0.75 |
| 8
|
16 to 23 |
21 to 46 |
0.5 to 0.75 |
| 9
|
18 to 27 |
24 to 54 |
0.5 to 0.75 |
|
10 |
20 to 30 |
27 to 60 |
0.5 to 0.75 |
|
15 |
30 to 45 |
40 to 90 |
0.5 to 0.75 |
|
20 |
40 to 60 |
53 to 120 |
0.5 to 0.75
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Trunk Implants:
Iron sulfate, or chelate iron in
caplets can be implanted directly into the tree trunk,
which is released into the trees water transport
system to correct iron chlorosis . Implant holes are
drilled into the tree and based on the severity of
iron deficiency determines the number of implants and
also the proper placement is most important to obtain
the best results. A normal response occurs in two to
three weeks in early spring after the full leaves are
out and four to five weeks in summer. Retreatment may
not be required for two to three years. The implant
wounds are usually small and callous tissue will close
the wounds within a year. This is probably the most
effect method of treatment and will require regular
retreatment in order to maintain a conditional
health for the lifetime of your tree. It would be
better to avoid tree species that are indigenous to
our area and high alkaline soils.
Iron deficiency is not the only
cause of leaf yellowing, other mineral deficiencies
such as nitrogen, manganese, boron and zinc may also
result in chlorosis symptoms.
Light applications of ammonium
sulfate (21-0-0) with 24% sulfur and micro-nutrients
applied three to four times a year will improve the
health of the tree. It is important to understand
that the alkalinity of the soils is 4 to 5 ft deep and
any attempt to correct and lower the soil pH is futile
and only a temporary alternative and the pH will ounce
back. |
