• TABLE OF CONTENTS
HIDE
 Copyright
 What is iron chlorosis
 How is iron taken up by the...
 Why are chlorotic plants undes...
 What are iron chelates
 Recommend chelates for rockdale...
 Methods of application and...
 Preventive maintenance program
 Combination of Fe chelates and...
 The application of chelates through...
 Testing of new chelates
 Conclusions and recommendation...
 List of Tables














Group Title: AREC-H research report - Agricultural Research and Education Center-Homestead ; SB-74-3
Title: Correction of iron chlorosis of avocados growing on Rockdale soils in the Homestead area
CITATION PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00067829/00001
 Material Information
Title: Correction of iron chlorosis of avocados growing on Rockdale soils in the Homestead area
Series Title: Homestead AREC research report
Physical Description: 8 leaves : ; 28 cm.
Language: English
Creator: Malo, Simâon E
Agricultural Research and Education Center, Homestead
Publisher: University of Florida, Agricultural Research and Education Center
Place of Publication: Homestead Fla
Publication Date: 1974
 Subjects
Subject: Avocado -- Diseases and pests -- Florida -- Miami-Dade County   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: Simon Malo E.
General Note: "February 15, 1974."
 Record Information
Bibliographic ID: UF00067829
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 72444501

Table of Contents
    Copyright
        Copyright
    What is iron chlorosis
        Page 1
    How is iron taken up by the plant
        Page 1
    Why are chlorotic plants undesirable
        Page 1
    What are iron chelates
        Page 2
    Recommend chelates for rockdale soils
        Page 2
    Methods of application and rates
        Page 3
    Preventive maintenance program
        Page 3
    Combination of Fe chelates and aluminum sulfate
        Page 4
    The application of chelates through trickle irrigation system
        Page 4
    Testing of new chelates
        Page 4
    Conclusions and recommendations
        Page 5
    List of Tables
        Page 6
        Page 7
        Page 8
Full Text





HISTORIC NOTE


The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
(EDIS)

site maintained by the Florida
Cooperative Extension Service.






Copyright 2005, Board of Trustees, University
of Florida






Homestead AREC Research Report SB74-3 February 15, 1974

CORRECTION OF IRON CHLOROSIS OF AVOCADOS GROWING
ON ROCKDALE SOILS IN THE HOMESTEAD AREA

ME LIBRARY Simon E. Mal
Associate Horticulturist
University of Florida
SP. 1 1974 Institute of Food and Agricultural Sciences
Agricultural Research and Education Center
SIHomestead
i.F Univ. of Florida
at o osis"

Chlorosis or the yellowing of plant leaves so commonly observed in the Homestead area,
is often due to a deficiency of iron (Fe in chemical notation) in plants. Without
iron leaves cannot manufacture chlorophyll, which is the substance that captures the
energy from the sun in the life-sustaining process of photosynthesis for the produc-
tion of basic organic compounds. Thus iron, although required in very small amounts,
is essential for plant life, and is particularly important for the best performance
of high yielding fruit trees.

How is Iron taken up by the plant.

Iron in the soil must be in soluble form for plant roots to absorb it. The calcare-
ous Rockdale soils of the Homestead area have the tendency to fix iron in insoluble
and therefore unavailable forms. Consequently, regardless of how much total iron is
contained in the soil particles, the plant cannot obtain it. This results in iron
deficiency chlorosis. The nature of iron utilization in plants is such that even
within cells it can become fixed or tied up in forms that cannot be utilized in
chlorophyll production. If this happens it won't be translocated from older green
leaves to young, expanding new tissue, resulting in the formation of stunted and
chlorotic new shoots. In the majority of plants iron is obtained solely through root
absorption from the soil. Only in few cases are plants capable of absorbing iron
directly through the leaves. When this happens only those leaves into which iron
was absorbed directly turn green.

Why are chlorotic plants undesirable.

Chlorotic plants are almost inevitably weak and undernourished because of the insuf-
ficiency of chlorophyll in their leaves for photosynthesis and the manufacture of
plant food for growth and fruit production. Plants in this condition do not respond
in a normal manner to grove practices such as irrigation and fertilization. Their
generally small and weak root system is easily damaged by an excess of fertilizer
salts and irrigation water. Fruit production is reduced and often is unmarketable
because of poor quality.

Most fruit trees in the calcareous Rockdale soils of Homestead are affected by iron
deficiency at one time or another. Avocado trees have traditionally shown a high
susceptibility to iron chlorosis and need special attention. Since individual trees
and varieties vary in their susceptibility or tendency to chlorosis, constant grove
supervision is necessary to locate and treat trees beginning to show Fe deficiency.
If not treated promptly, a chlorotic tree progressively declines to the point where
it needs a rather large investment in time, materials and care to put it back on its
feet. As is true with most fruit tree problems, an ounce of prevention is worth
Pounds of costly, corrective measures.






Homestead AREC Research Report SB74-3 February 15, 1974

CORRECTION OF IRON CHLOROSIS OF AVOCADOS GROWING
ON ROCKDALE SOILS IN THE HOMESTEAD AREA

ME LIBRARY Simon E. Mal
Associate Horticulturist
University of Florida
SP. 1 1974 Institute of Food and Agricultural Sciences
Agricultural Research and Education Center
SIHomestead
i.F Univ. of Florida
at o osis"

Chlorosis or the yellowing of plant leaves so commonly observed in the Homestead area,
is often due to a deficiency of iron (Fe in chemical notation) in plants. Without
iron leaves cannot manufacture chlorophyll, which is the substance that captures the
energy from the sun in the life-sustaining process of photosynthesis for the produc-
tion of basic organic compounds. Thus iron, although required in very small amounts,
is essential for plant life, and is particularly important for the best performance
of high yielding fruit trees.

How is Iron taken up by the plant.

Iron in the soil must be in soluble form for plant roots to absorb it. The calcare-
ous Rockdale soils of the Homestead area have the tendency to fix iron in insoluble
and therefore unavailable forms. Consequently, regardless of how much total iron is
contained in the soil particles, the plant cannot obtain it. This results in iron
deficiency chlorosis. The nature of iron utilization in plants is such that even
within cells it can become fixed or tied up in forms that cannot be utilized in
chlorophyll production. If this happens it won't be translocated from older green
leaves to young, expanding new tissue, resulting in the formation of stunted and
chlorotic new shoots. In the majority of plants iron is obtained solely through root
absorption from the soil. Only in few cases are plants capable of absorbing iron
directly through the leaves. When this happens only those leaves into which iron
was absorbed directly turn green.

Why are chlorotic plants undesirable.

Chlorotic plants are almost inevitably weak and undernourished because of the insuf-
ficiency of chlorophyll in their leaves for photosynthesis and the manufacture of
plant food for growth and fruit production. Plants in this condition do not respond
in a normal manner to grove practices such as irrigation and fertilization. Their
generally small and weak root system is easily damaged by an excess of fertilizer
salts and irrigation water. Fruit production is reduced and often is unmarketable
because of poor quality.

Most fruit trees in the calcareous Rockdale soils of Homestead are affected by iron
deficiency at one time or another. Avocado trees have traditionally shown a high
susceptibility to iron chlorosis and need special attention. Since individual trees
and varieties vary in their susceptibility or tendency to chlorosis, constant grove
supervision is necessary to locate and treat trees beginning to show Fe deficiency.
If not treated promptly, a chlorotic tree progressively declines to the point where
it needs a rather large investment in time, materials and care to put it back on its
feet. As is true with most fruit tree problems, an ounce of prevention is worth
Pounds of costly, corrective measures.






Homestead AREC Research Report SB74-3 February 15, 1974

CORRECTION OF IRON CHLOROSIS OF AVOCADOS GROWING
ON ROCKDALE SOILS IN THE HOMESTEAD AREA

ME LIBRARY Simon E. Mal
Associate Horticulturist
University of Florida
SP. 1 1974 Institute of Food and Agricultural Sciences
Agricultural Research and Education Center
SIHomestead
i.F Univ. of Florida
at o osis"

Chlorosis or the yellowing of plant leaves so commonly observed in the Homestead area,
is often due to a deficiency of iron (Fe in chemical notation) in plants. Without
iron leaves cannot manufacture chlorophyll, which is the substance that captures the
energy from the sun in the life-sustaining process of photosynthesis for the produc-
tion of basic organic compounds. Thus iron, although required in very small amounts,
is essential for plant life, and is particularly important for the best performance
of high yielding fruit trees.

How is Iron taken up by the plant.

Iron in the soil must be in soluble form for plant roots to absorb it. The calcare-
ous Rockdale soils of the Homestead area have the tendency to fix iron in insoluble
and therefore unavailable forms. Consequently, regardless of how much total iron is
contained in the soil particles, the plant cannot obtain it. This results in iron
deficiency chlorosis. The nature of iron utilization in plants is such that even
within cells it can become fixed or tied up in forms that cannot be utilized in
chlorophyll production. If this happens it won't be translocated from older green
leaves to young, expanding new tissue, resulting in the formation of stunted and
chlorotic new shoots. In the majority of plants iron is obtained solely through root
absorption from the soil. Only in few cases are plants capable of absorbing iron
directly through the leaves. When this happens only those leaves into which iron
was absorbed directly turn green.

Why are chlorotic plants undesirable.

Chlorotic plants are almost inevitably weak and undernourished because of the insuf-
ficiency of chlorophyll in their leaves for photosynthesis and the manufacture of
plant food for growth and fruit production. Plants in this condition do not respond
in a normal manner to grove practices such as irrigation and fertilization. Their
generally small and weak root system is easily damaged by an excess of fertilizer
salts and irrigation water. Fruit production is reduced and often is unmarketable
because of poor quality.

Most fruit trees in the calcareous Rockdale soils of Homestead are affected by iron
deficiency at one time or another. Avocado trees have traditionally shown a high
susceptibility to iron chlorosis and need special attention. Since individual trees
and varieties vary in their susceptibility or tendency to chlorosis, constant grove
supervision is necessary to locate and treat trees beginning to show Fe deficiency.
If not treated promptly, a chlorotic tree progressively declines to the point where
it needs a rather large investment in time, materials and care to put it back on its
feet. As is true with most fruit tree problems, an ounce of prevention is worth
Pounds of costly, corrective measures.









Recent studies on the nature of chlorosis and its effects on fruit tree performance
* indicate that Fe deficiency reduces fruit production in avocado even before visible
symptoms of chlorosis are apparent. Experiments involving low annual treatments of
chelates to trees without obvious visible symptoms of Fe chlorosis have resulted in
increased yields which at present appear sufficient to justify the investment of
time, labor and chemicals in a program of preventive applications of Fe-chelates.

What are iron chelates.

Chelates are complex chemicals which generally supply essential elements to plant
roots under soil conditions where these elements often become tied-up in unavailable
forms. Most iron chelates degrade or lose their chemical activity under very alka-
line or calcareous conditions. However, some chelates such as "Sequestrene 138"
(HFeEDDHA), maintain its stability for considerable time even under very alkaline
conditions enabling plant roots to benefit from its iron carrying ability. In con-
trast to most essential elements, the nature of iron in plant metabolism is such
that iron salts and chelates are not absorbed through the foliage or are absorbed in
small quantities but not enough to justify their use in this manner. Thus, the
majority of fruit tree species do not have the ability to utilize iron through the
leaves and should be treated with soil applications of chelates to correct Fe chlo-
rosis. Many years of testing innumerable sources of iron and iron chelates in the
calcareous soils of the Homestead area have shown that only a few have the ability
to effectively correct acute chlorosis symptoms under these local conditions. Of
these Sequestrene Fe-138 is by far the most effective when properly used as a soil
drench or injected as a water solution directly into the root area of chlorotic trees.

Recommended chelates for Rockdale soils.

Sequestrene Fe-138 is a very expensive product to manufacture and at present, con-
sidering the cost of raw materials, it is unlikely that its price to the grower will
be reduced substantially. Based on several years of searching for a cheaper but just
as effective substitute for Sequestrene Fe-138 and after persistently evaluating the
effect of this chelate on fruit yields, we have repeatedly come to the conclusion
that, in spite of its cost, it is the only chelate that we should recommend to the
Homestead area avocado grower, at least until newer, less costly and just as effec-
tive materials appear in the market. The results which support these conclusions
are presented here for the benefit of the reader.

Table 1 and 2 summarize results of several years of evaluating the performance of
several chelates and combinations on the yield of 'Lula' avocados. Sequestrene Fe-
138 is ahead of all others not only in accumulated tree production but perhaps just
as importantly in the overall quality of the fruit obtained. Annual evaluation of
crop condition revealed that none of the fruit in other treatments approached the
deep green color of fruit from trees receiving 1.0 lbs of Seq. 138 per tree/year.
The 'Lula' variety was chosen because it is perhaps the most susceptible to Fe chlo-
rosis, particularly if the trees are situated at the edge of a glade, as was the case
with this experimental grove. The high rate used here was for corrective measures
and because this was a problem grove with a history of recurrent chlorosis. It should
be stressed again that under average conditions it is better to use lower rates of
chelates in an annual preventive program, to forestall the development of Fe chlo-
rosis, than to require corrective measures. Once a tree has been allowed to become
chlorotic it loses a good part of its root system and reacts very slowly even to
massive does of chelates. Normal production is usually resumed only after the second
year of chelate applications.









Recent studies on the nature of chlorosis and its effects on fruit tree performance
* indicate that Fe deficiency reduces fruit production in avocado even before visible
symptoms of chlorosis are apparent. Experiments involving low annual treatments of
chelates to trees without obvious visible symptoms of Fe chlorosis have resulted in
increased yields which at present appear sufficient to justify the investment of
time, labor and chemicals in a program of preventive applications of Fe-chelates.

What are iron chelates.

Chelates are complex chemicals which generally supply essential elements to plant
roots under soil conditions where these elements often become tied-up in unavailable
forms. Most iron chelates degrade or lose their chemical activity under very alka-
line or calcareous conditions. However, some chelates such as "Sequestrene 138"
(HFeEDDHA), maintain its stability for considerable time even under very alkaline
conditions enabling plant roots to benefit from its iron carrying ability. In con-
trast to most essential elements, the nature of iron in plant metabolism is such
that iron salts and chelates are not absorbed through the foliage or are absorbed in
small quantities but not enough to justify their use in this manner. Thus, the
majority of fruit tree species do not have the ability to utilize iron through the
leaves and should be treated with soil applications of chelates to correct Fe chlo-
rosis. Many years of testing innumerable sources of iron and iron chelates in the
calcareous soils of the Homestead area have shown that only a few have the ability
to effectively correct acute chlorosis symptoms under these local conditions. Of
these Sequestrene Fe-138 is by far the most effective when properly used as a soil
drench or injected as a water solution directly into the root area of chlorotic trees.

Recommended chelates for Rockdale soils.

Sequestrene Fe-138 is a very expensive product to manufacture and at present, con-
sidering the cost of raw materials, it is unlikely that its price to the grower will
be reduced substantially. Based on several years of searching for a cheaper but just
as effective substitute for Sequestrene Fe-138 and after persistently evaluating the
effect of this chelate on fruit yields, we have repeatedly come to the conclusion
that, in spite of its cost, it is the only chelate that we should recommend to the
Homestead area avocado grower, at least until newer, less costly and just as effec-
tive materials appear in the market. The results which support these conclusions
are presented here for the benefit of the reader.

Table 1 and 2 summarize results of several years of evaluating the performance of
several chelates and combinations on the yield of 'Lula' avocados. Sequestrene Fe-
138 is ahead of all others not only in accumulated tree production but perhaps just
as importantly in the overall quality of the fruit obtained. Annual evaluation of
crop condition revealed that none of the fruit in other treatments approached the
deep green color of fruit from trees receiving 1.0 lbs of Seq. 138 per tree/year.
The 'Lula' variety was chosen because it is perhaps the most susceptible to Fe chlo-
rosis, particularly if the trees are situated at the edge of a glade, as was the case
with this experimental grove. The high rate used here was for corrective measures
and because this was a problem grove with a history of recurrent chlorosis. It should
be stressed again that under average conditions it is better to use lower rates of
chelates in an annual preventive program, to forestall the development of Fe chlo-
rosis, than to require corrective measures. Once a tree has been allowed to become
chlorotic it loses a good part of its root system and reacts very slowly even to
massive does of chelates. Normal production is usually resumed only after the second
year of chelate applications.









Methods of application and rates.

SSequestrene 138 is susceptible to ultraviolet light degradation and should not remain
on the surface of the soil exposed to sunlight for many hours. A good method of ap-
plying it is as a soil drench, making sure to wash the chelate down to the root area
with abundant water. Drenching is very adequate for treating a few, small trees but
it becomes time consuming and expensive when treating a larger number of trees in a
a producing grove. A more mechanized and faster manner of applying the chelate is
by injecting it into the soil as a water suspension directly into the root zone of
the tree.

Table 3 gives recommended amounts of Sequestrene Fe-138 as corrective treatments for
most avocado trees. Notice that the table includes most tree ages and 3 stages of
chlorosis; however, more chelate may be needed for stubborn, isolated cases. The
grower should remember that the area near the trunk of a tree (within 2-3 feet) con-
tains the highest concentration of roots and chelates should preferably be applied
in this area.

Preventive maintenance program.

The lower rates recommended for trees suffering incipient chlorosis appear sufficient
for use on trees in a preventive maintenance program. Starting with an annual ap-
plication of k oz. or less for small, recently planted trees and progressing to no
more than 4.0 oz. for large, older trees. The best time for this annual application
is during the month of October or right after the rainy season when the plant's root
system is at maximum expansion. Repeated root studies have shown that avocado feeder
roots in Rockdale soil die back gradually during the dry season and reach their mini-
* mum spread sometime in May, even under irrigated conditions.

It has long been a common observation by plant physiologists working with iron nutri-
tion that the foliage of certain plants which has been chlorotic for considerable
time reverts back very slowly to its normal color after chelate application but sel-
dom attains its normal size. This is also a common observation in the Homestead area,
particularly with young container grown trees of lychee, mango, mamey sapote, avocado,
citrus and others. This emphasizes the point that it is better to prevent chlorosis
than to correct it after it occurs.

Evidence for the desirability of establishing a chelate application program to pre-
vent chlorosis comes fromstudies being conducted with young 'Ruehle' and 'Simmonds'
avocados. These trees, particularly 'Ruehle', have seldom shown symptoms of chloro-
sis, although 'Simmonds' tends to show some Fe deficiency symptoms in late summer
and fall after the crop is off the tree.

The 4 years results summarized in Table 4 show a net gain of 0.53 and 0.43 of a
bushel per tree (a total difference of 169.6 and 137.5 bushels for 80 trees) between
the controls with no treatment and those receiving 4.0 oz. and 2.0 oz. of Seq. 138
respectively. The other treatments also show considerable gains. However, a calcu-
lation of net cost to produce an additional bushel over the control reveals that at
present chelate prices it cost 29 and 18 cents per bushel for the 4.0 oz. and 2.0 oz.
Seq. 138 treatments, respectively. It costs 25 cents for Versenol alone and 35 cents
for Versenol plus aluminum sulfate. Considering this investment in chelates and
their effect in terms of fruit quality and return to the grower, it can be concluded
that a better business decision would be to use 2.0 oz. of Seq. 138 which brings good
results at the lowest cost of 18 cents/bushel. The fruit from trees receiving Ver-
senol alone or in combinations, has invariably been inferior in overall quality,
color and even size.









Methods of application and rates.

SSequestrene 138 is susceptible to ultraviolet light degradation and should not remain
on the surface of the soil exposed to sunlight for many hours. A good method of ap-
plying it is as a soil drench, making sure to wash the chelate down to the root area
with abundant water. Drenching is very adequate for treating a few, small trees but
it becomes time consuming and expensive when treating a larger number of trees in a
a producing grove. A more mechanized and faster manner of applying the chelate is
by injecting it into the soil as a water suspension directly into the root zone of
the tree.

Table 3 gives recommended amounts of Sequestrene Fe-138 as corrective treatments for
most avocado trees. Notice that the table includes most tree ages and 3 stages of
chlorosis; however, more chelate may be needed for stubborn, isolated cases. The
grower should remember that the area near the trunk of a tree (within 2-3 feet) con-
tains the highest concentration of roots and chelates should preferably be applied
in this area.

Preventive maintenance program.

The lower rates recommended for trees suffering incipient chlorosis appear sufficient
for use on trees in a preventive maintenance program. Starting with an annual ap-
plication of k oz. or less for small, recently planted trees and progressing to no
more than 4.0 oz. for large, older trees. The best time for this annual application
is during the month of October or right after the rainy season when the plant's root
system is at maximum expansion. Repeated root studies have shown that avocado feeder
roots in Rockdale soil die back gradually during the dry season and reach their mini-
* mum spread sometime in May, even under irrigated conditions.

It has long been a common observation by plant physiologists working with iron nutri-
tion that the foliage of certain plants which has been chlorotic for considerable
time reverts back very slowly to its normal color after chelate application but sel-
dom attains its normal size. This is also a common observation in the Homestead area,
particularly with young container grown trees of lychee, mango, mamey sapote, avocado,
citrus and others. This emphasizes the point that it is better to prevent chlorosis
than to correct it after it occurs.

Evidence for the desirability of establishing a chelate application program to pre-
vent chlorosis comes fromstudies being conducted with young 'Ruehle' and 'Simmonds'
avocados. These trees, particularly 'Ruehle', have seldom shown symptoms of chloro-
sis, although 'Simmonds' tends to show some Fe deficiency symptoms in late summer
and fall after the crop is off the tree.

The 4 years results summarized in Table 4 show a net gain of 0.53 and 0.43 of a
bushel per tree (a total difference of 169.6 and 137.5 bushels for 80 trees) between
the controls with no treatment and those receiving 4.0 oz. and 2.0 oz. of Seq. 138
respectively. The other treatments also show considerable gains. However, a calcu-
lation of net cost to produce an additional bushel over the control reveals that at
present chelate prices it cost 29 and 18 cents per bushel for the 4.0 oz. and 2.0 oz.
Seq. 138 treatments, respectively. It costs 25 cents for Versenol alone and 35 cents
for Versenol plus aluminum sulfate. Considering this investment in chelates and
their effect in terms of fruit quality and return to the grower, it can be concluded
that a better business decision would be to use 2.0 oz. of Seq. 138 which brings good
results at the lowest cost of 18 cents/bushel. The fruit from trees receiving Ver-
senol alone or in combinations, has invariably been inferior in overall quality,
color and even size.










Combination of Fe chelates and Aluminum sulfate.

The addition of aluminum sulfate to chelates such as EDTA has appeared in the past
to increase the absorption of iron from Na2FeEDTA. In order to test the response of
this combination in fruit yield performance, two long term experiments were set up
in 1969 with large numbers of replicated trees of the same variety in order to mini-
mize the well known coefficient of production variability exhibited by avocado trees.
Table 1 shows that 'Lula' trees receiving the combination 1.5 Ib EDTA (14% Fe) plus
2.0 lb aluminum sulfate produced, in 5 years, an average of 0.44 bushel/tree more
than those receiving 1.5 lb of EDTA alone. However, results in Table 4 show that the
same was not true with 'Ruehle' trees receiving "Versenol" (EEDTA) plus aluminum
sulfate. For the period of 4 years, trees receiving only "Versenol" average slightly
more than those receiving the combination. The number of tree replications used in
this experiment was almost twice the amount used in the first, thus increasing ac-
curacy in this manner. The data showed that aluminum sulfate did not have any effect
on the absorption of iron from EEDTA, while it did appear to have an effect on EDTA.
In view of the nature of the annual variability of avocado production it is necessary
to continue this work for a few years longer to determine more accurately the com-
mercial feasibility of this combination, and also the long term effect of aluminum
sulfate on the tree. Experience demonstrates that long-term application of metallic
ions can result in accumulations which adversely affect plant development.

The application of chelates through trickle irrigation system.

After 2k years of experimental studies trickle irrigation is perhaps the best method
for treating avocado with Fe chelates when small amounts of soluble chelates are used
in a frequently and sustained manner. This was true even with materials which would
not work at all in the conventional manner of application.

Although it is not precisely known why trickle application of chelates is more suc-
cessful than other methods, it can be speculated that more chelate is absorbed be-
cause it comes in contact almost immediately after discharge with a large mass of
young, active feeder roots growing in the moist soil below the trickier. Apparently
the chelate is removed from the soil solution before the chemical reactions of inac-
tivation take place, which would normally occur if the chelate remains in contact
with the soil particles even for short periods of time.

Although we need to research more fully into the area of application of soluble
chemicals through trickle irrigation systems, we have enough experience at this time
to know that the possibilities of effectively using moderately priced materials with
less stability than Sequestrene 138 appears to be good.

Testing of new chelates.

The evaluation of new chelates and sources of iron as they become available continues
at the Agr. Res. & Educ. Center. At present two very promising materials are being
tested for effectiveness under our calcareous conditions. They both appear to be
less costly than Seq. Fe-138 and have the additional advantage of being completely
soluble which makes them ideally suited for application through "trickle" irrigation
systems. However, before any recommendations to the grower are made it is necessary
Sto obtain at least 4 years of performance records under a variety of conditions.










Combination of Fe chelates and Aluminum sulfate.

The addition of aluminum sulfate to chelates such as EDTA has appeared in the past
to increase the absorption of iron from Na2FeEDTA. In order to test the response of
this combination in fruit yield performance, two long term experiments were set up
in 1969 with large numbers of replicated trees of the same variety in order to mini-
mize the well known coefficient of production variability exhibited by avocado trees.
Table 1 shows that 'Lula' trees receiving the combination 1.5 Ib EDTA (14% Fe) plus
2.0 lb aluminum sulfate produced, in 5 years, an average of 0.44 bushel/tree more
than those receiving 1.5 lb of EDTA alone. However, results in Table 4 show that the
same was not true with 'Ruehle' trees receiving "Versenol" (EEDTA) plus aluminum
sulfate. For the period of 4 years, trees receiving only "Versenol" average slightly
more than those receiving the combination. The number of tree replications used in
this experiment was almost twice the amount used in the first, thus increasing ac-
curacy in this manner. The data showed that aluminum sulfate did not have any effect
on the absorption of iron from EEDTA, while it did appear to have an effect on EDTA.
In view of the nature of the annual variability of avocado production it is necessary
to continue this work for a few years longer to determine more accurately the com-
mercial feasibility of this combination, and also the long term effect of aluminum
sulfate on the tree. Experience demonstrates that long-term application of metallic
ions can result in accumulations which adversely affect plant development.

The application of chelates through trickle irrigation system.

After 2k years of experimental studies trickle irrigation is perhaps the best method
for treating avocado with Fe chelates when small amounts of soluble chelates are used
in a frequently and sustained manner. This was true even with materials which would
not work at all in the conventional manner of application.

Although it is not precisely known why trickle application of chelates is more suc-
cessful than other methods, it can be speculated that more chelate is absorbed be-
cause it comes in contact almost immediately after discharge with a large mass of
young, active feeder roots growing in the moist soil below the trickier. Apparently
the chelate is removed from the soil solution before the chemical reactions of inac-
tivation take place, which would normally occur if the chelate remains in contact
with the soil particles even for short periods of time.

Although we need to research more fully into the area of application of soluble
chemicals through trickle irrigation systems, we have enough experience at this time
to know that the possibilities of effectively using moderately priced materials with
less stability than Sequestrene 138 appears to be good.

Testing of new chelates.

The evaluation of new chelates and sources of iron as they become available continues
at the Agr. Res. & Educ. Center. At present two very promising materials are being
tested for effectiveness under our calcareous conditions. They both appear to be
less costly than Seq. Fe-138 and have the additional advantage of being completely
soluble which makes them ideally suited for application through "trickle" irrigation
systems. However, before any recommendations to the grower are made it is necessary
Sto obtain at least 4 years of performance records under a variety of conditions.










Combination of Fe chelates and Aluminum sulfate.

The addition of aluminum sulfate to chelates such as EDTA has appeared in the past
to increase the absorption of iron from Na2FeEDTA. In order to test the response of
this combination in fruit yield performance, two long term experiments were set up
in 1969 with large numbers of replicated trees of the same variety in order to mini-
mize the well known coefficient of production variability exhibited by avocado trees.
Table 1 shows that 'Lula' trees receiving the combination 1.5 Ib EDTA (14% Fe) plus
2.0 lb aluminum sulfate produced, in 5 years, an average of 0.44 bushel/tree more
than those receiving 1.5 lb of EDTA alone. However, results in Table 4 show that the
same was not true with 'Ruehle' trees receiving "Versenol" (EEDTA) plus aluminum
sulfate. For the period of 4 years, trees receiving only "Versenol" average slightly
more than those receiving the combination. The number of tree replications used in
this experiment was almost twice the amount used in the first, thus increasing ac-
curacy in this manner. The data showed that aluminum sulfate did not have any effect
on the absorption of iron from EEDTA, while it did appear to have an effect on EDTA.
In view of the nature of the annual variability of avocado production it is necessary
to continue this work for a few years longer to determine more accurately the com-
mercial feasibility of this combination, and also the long term effect of aluminum
sulfate on the tree. Experience demonstrates that long-term application of metallic
ions can result in accumulations which adversely affect plant development.

The application of chelates through trickle irrigation system.

After 2k years of experimental studies trickle irrigation is perhaps the best method
for treating avocado with Fe chelates when small amounts of soluble chelates are used
in a frequently and sustained manner. This was true even with materials which would
not work at all in the conventional manner of application.

Although it is not precisely known why trickle application of chelates is more suc-
cessful than other methods, it can be speculated that more chelate is absorbed be-
cause it comes in contact almost immediately after discharge with a large mass of
young, active feeder roots growing in the moist soil below the trickier. Apparently
the chelate is removed from the soil solution before the chemical reactions of inac-
tivation take place, which would normally occur if the chelate remains in contact
with the soil particles even for short periods of time.

Although we need to research more fully into the area of application of soluble
chemicals through trickle irrigation systems, we have enough experience at this time
to know that the possibilities of effectively using moderately priced materials with
less stability than Sequestrene 138 appears to be good.

Testing of new chelates.

The evaluation of new chelates and sources of iron as they become available continues
at the Agr. Res. & Educ. Center. At present two very promising materials are being
tested for effectiveness under our calcareous conditions. They both appear to be
less costly than Seq. Fe-138 and have the additional advantage of being completely
soluble which makes them ideally suited for application through "trickle" irrigation
systems. However, before any recommendations to the grower are made it is necessary
Sto obtain at least 4 years of performance records under a variety of conditions.









CONCLUSIONS AND RECOMMENDATIONS

I. Before we had any effective corrective treatment for Fe chlorosis there was no
way of properly determining its significance on the fruit production of avocado
trees in the Homestead area. However, in recent years research has conclusively
shown that avocados growing in calcareous Rockdale soil, and particularly chlo-
rotic trees, cannot realize their maximum variety potential unless properly
treated with Fe chelates.
2. The 'Lula' variety appears to be the most susceptible to iron deficiency. A
sustained program of chelate application in 'Lula' groves with a history of
chlorosis has resulted in 5-fold increases in fruit production compared with
control trees with no chelate application.
3. Long term studies of more than 9 years have shown that at present Sequestrene
Fe-138 (Ferric chelate of Ethylenediamine (di-(O-hydroxphenylacetate)-HeFeEDDHA)
is the chelate which brings better yields of better fruit quality than any other
chelate tested in the Homestead area. Studies of returns to the grower have
shown that Seq. 138 has invariably an advantage over other chelates in producing
a higher profit per dollar of chelate invested.
4. A preventative maintenance program of Seq. 138 injected into the soil around the
trunk of a tree, during the month of October, appears to give, in the long run,
better results than large corrective dosages applied sporadically to isolated
trees. Very small and frequent application of chelates with trickle irrigation
appear at present, to have good possibilities for the future.
5. The timing of the treatment and the manner of application are just as critical
as the amount of Seq. 138 used. Chlorotic trees which have been allowed to
deteriorate are difficult to bring back to good condition due to a reduced root
system and may need up to 3 years of annual treatments to attain their full
S potential in fruit production.
6. Although Seq. 138 corrects iron deficiency better than the other materials tested,
increases in yield also occurred with EDTA and Versenol treatments. The possible
adverse effects of these materials in combination with aluminum sulfate have not
been fully evaluated and need further study. Caution in using aluminum sulfate
is advised since it is not known what effect accumulations of this metal in the
soil may have.











Table 1. Average annual yield of fruit per
'Lula' avocado receiving several chelate
consisting of 25 trees per treatment.


tree (bushels) for
treatments and


Treatments
Year 1 2 3 4 4a 5

1970 3.24 1.79 2.06 3.84 -- 0.81
1971 6.66 5.08 5.02 2.35 5.68 1.91
1972 7.47 6.89 5.58 4.37 5.57 2.40
1973 5.04 3.88 3.04 0.89 2.96 1.96
1974 5.85 4.94 4.68 (3.24)* -- (6.17)*

Avg. 5.65a** 4.51ab 4.07bc 2.86cd 4.73 1.77d
(4 yrs. (3 yrs. (Apx. 5
only) only) yrs.)


Treatments
1. Seq. Fe-138:1.0 lb/tree per year.
2. EDTA (14% Fe) 1.5 lb + 2.0 Al2 (SO4)3/tree per year.
3. EDTA (14% Fe) 1.5 Ib/tree per year.
4. Fe-157 1.0 lbs/tree per year.
4a. Fe-157 2.0 lb/tree per year.
5. Control.

* Averages for Treat. 4 and 5 have drastically changed in
1974. Treat. 4 was not applied in order to determine how
fast it took for trees to deteriorate without a chelate
treatment. The control, Treat. 5 received 1.0 lb. of Seq.
138 to determine the recovery rate of trees which had re-
mained in a severe chlorosis. Treat. 4a was discontinued
because production of Fe-157 was also discontinued.
** Treatments followed by same letter are not significantly
different among themselves.







Table 2. Total annual production
tions and consisting of

Fruit
Year I color* 2

1970 81.05 1.0 44.75
1971 166.50 1.0 127.10
1972 186.80 1.5 172.40
1973 126.00 1.0 97.00
1974 146.25 1.5 123.65


Total

Avg. Fruit

Return***


706.60

Color

$53.67


564.90


of 'Lula' trees receiving several Fe-chelate applica-
25 trees per treatment.

Fruit Fruit Fruit Fruit
color 3 color 4 color 5 color

2.0 51.55 2.0 96.15 2.5 20.35 2.5
2.5 125.50 2.5 58.75 2.0 47.75 3.0
3.0 139.50 3.0 109.40 2.5 60.20 3.5
2.0 76.20 2.0 22.30 2.0 49.20 4.0
3.0 117.00 3.0 (81.00) 3.5 (160.50) 2.5


509.75


2.5


$42.84


286.60


2.5


$38.66


(4 yrs.)

2.25


$27.07


221.50**


3.25


$16.81


Fruit color. Estimated values. 1 = Deep green, 2 = Light green, 3 = Moderately
chlorotic, 4 = Chlorotic, 5 = Very chlorotic.

** The fifth year was estimated by obtaining the average of the other 4 years.

*** Gross return per tree to the grower disregarding fruit quality (color) was calculated
on basis of an average price of $9.50/bushel during the last week of Jan. 1974.

Table 3. Condition of tree and amount of "Seq. 138" needed
to correct chlorosis.


Chlorosis
Tree age Incipient Moderate Severe

0-1 years 4-1 oz. 1-2 oz. 2-3 oz.

2-4 years 1-2 oz. 2-4 oz. 4-6 oz.

5-7 years 2-3 oz. 3-6 oz. 4-8 oz.

9 and older 4-6 oz. 8-12 oz. 12-16 oz.














Table 4.

Variety

Ruehle
Simmonds

Ruehle
Simmonds

Ruehle
Simmonds

s Ruehle
Simmonds

Ruehle
Simmonds


Yield of trees (bushels) under a preventive

No. trees Treatment

80 Sequestrene 138 4 oz
80 "

80 Sequestrene 138 2.0 oz
80 ii if It 12

40 Versenol 2.0 lb
40 "

40 Ver. 2.0 lb + Ilb Al (S04)3
40 "

80 Control
80 "


maintenance program of

1970 1971 1972 1973

1.07 1.75 1.86 1.20
1.36 2.15

1.05 1.45 1.91 1.07
1.31 1.88

1.08 1.28 1.93 1.07
1.10 1.97

1.04 1.28 1.83 0.98
1.27 1.77

0.99 0.98 1.34 0.46
1.25 1.82


chelates..

Avg.

1.47a*


Total**

472.25


1.37a 440.1


1.34a 215.1


1.28a 206.25


0.94b 302.6


* Treatments followed by same letter are not significantly different among themselves.
** Total yield of all trees in treatment.

1970 and 1971 yields for 'Simmonds' were not taken due to communications and labor problems.














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