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Chronic Iron Deficiency In Plants
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Bulletin #TP2615
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Soil chemistry is the key to success |
This is an excerpt from a reprint of "Controlling Iron Chlorosis In Urban Mojave Desert Landscapes" by Bob Morris, Area Extension Specialist (Horticulture) Southern Nevada. The original is undated.
◊ Controlling Iron Chlorosis With Fertilizers
◊ Trunk Injection of Fertilizers
◊ List Plants that are susceptible
◊ Irrigation
◊ Plant Selection
◊Mulch
◊Root or Trunk Damage Prevention ◊
SUMMARY (end of
excerpt) ◊
List of Products with iron for prevention
The following is an excerpt from an article
by Bob Morris, Area Extension Specialist (Horticulture) Southern Nevada.
What is
Iron Chlorosis? Iron chlorosis is a yellowing of newer plant growth
caused by a lack of plant-available iron. Iron chlorosis gives the plant a
light green to yellow appearance. Closer inspection of the plant reveals that the
yellowing occurs between the veins of the leaf the veins remain green. This
is called interveinal chlorosis and in the Desert Southwest
is a fairly reliable indication
of an iron deficiency. As this condition worsens, leaves turn completely
yellow, scorch on the edges and drop from the tree. If no action is taken,
branches begin to die back and death can result. Other nutrient
deficiencies can cause chlorosis, but they do not respond to iron sprays. The
following simple test will determine if iron chlorosis is the problem: fill a
trigger spray bottle with iron sulfate (at one teaspoon per gallon) or iron
chelate solutions and spray the plant. Leaves sprayed with iron will turn
green in 24-48 hours. For reference, mark the sprayed branches with tape then,
in several days, compare them to the unsprayed branches. Soil-Applied
Fertilizers.
Soil applications of iron fertilizers should be
made between late fall and early spring, a few weeks before new growth starts.
Most organic fertilizers do not contain many
mineral supplements (such as iron), but some do.
Ir/on sulfate can also be
used for correcting iron chlorosis. However, research has indicated that
applications on highly alkaline soils are not as effective as Iron Chelate
products. Best results are obtained when iron sulfate is mixed with
agricultural soil sulfur in equal proportions.
Soil-applied fertilizers
should be placed beneath the soil surface with a shovel or probe.
Some products are sensitive to light and must not be left on the
soil surface, but can be used in conjunction
with root feeders or soil needles to a depth of about 12-18 inches, no deeper.
These products should be applied in many locations one application every two square feet is
ideal. After applying iron fertilizers, water deeply.
Table 1. Dosage for treating trees &
shrubs by soil application of a equal parts of iron (ferrous) sulfate &
sulfur Tree diameter Total amt. of iron
sulfate & sulfur per tree Number of holes in
ground around tree Total amt. of iron
sulfate & sulfur (1:1) in hole (inches) (pounds) (number) (pounds) 1 1 4 0.25 2 2 4 0.5 4 6 8 0.75 6 12 12 1.0 8 16-23 16-23 1.0-1.25 10 20-30 20-30 1.0-1.25 15 30-45 30-45 1.0-1.25 20 40-60 40-60 1.0-1.25 *Trees in bad condition
(some branches partially defoliated) should receive only one-half the amount of
the mixture given in the table.
Foliar-Applied
Fertilizers. An Iron solution sprayed on leaves gives the fastest
response, but affects only sprayed foliage. Repeat spraying will be needed
for some plants as new growth appears throughout the season. Iron sulfate is
an inexpensive foliar spray. Two and one-half ounces per three gallons or five
pounds per 100 gallons of finished spray should be used. Iron sulfate sprays
will stain cement, so they should be kept away from sidewalks, driveways,
stucco and light-colored walls. Iron sulfate sprays should not be used during
the heat they will burn foliage. Iron chelate sprays work and do not burn
foliage, but are more expensive to use.
Trunk
Injection of Fertilizers. Trunk applications (by certified Arborists) of iron fertilizers are
effective for controlling iron chlorosis up to three years. Timing of
injections should be in early spring with implants (capsules) and in late spring with
injections. Injections can be made with implants such as Medicaps®
gelatin capsules placed in holes drilled through the tree's bark) or by low pressure
injection (Mauget®).
Most often injection is done by trained
commercial arborists. Iron sulfate or ferric ammonium citrate are the two iron
compounds most commonly used. Whenever holes are drilled into living plant tissue,
plant damage occurs. Holes should be few and as small as possible.
Injection should be done only when trees can't be sprayed or receive soil applications.
Holes should be drilled in the root flares or as close to the ground as
possible. Tree response to iron injection is rapid. Excessive rates of
injected iron solutions will cause leaf drop.
Table
2. Urban Mojave Desert Landscape Plants Susceptible to
Iron Chlorosis Highly Susceptible Moderately
Susceptible Susceptible Aleppo pine Arborvitae African sumac Eucalyptus Ash Bottlebrush Photinia Cottonwood Chinaberry Pyracantha Fruit Trees Cotoneaster Heavenly bamboo Crape myrtle Junipers Indian hawthorn Locust Mulberry Pines Oleander Purple leaf plum Pineapple guava Rose Pittosporum Sycamore Podocarpus Willow Pomegranate Avoiding
Iron Chlorosis. Applying iron fertilizers may not cure the
problem. The underlying reason for the chlorosis must be identified to keep
it from recurring. Is the plant highly susceptible to iron chlorosis? Is it
getting too much water? Is the plant in a hot location? Does a soil test indicate
the plant needs iron? Besides greening up the leaves, underlying problems
should be corrected. Irrigation. A
common cause of iron chlorosis in urban desert areas is overwatering. Too
often sprinkler systems are designed to water lawns, trees and shrubs at the
same rate. Trees and shrubs in planted beds should be watered on a separate
sprinkler valve than frequently watered plants such as grass and annual flowers.
Trees and shrubs should be watered deeply and infrequently.
Plant
Selection. Some plants are more susceptible to iron
chlorosis than others (table 2) and their use should be limited in high-water
areas such as low spots, near sprinkler heads and on poorly drained locations.
Iron fertilizers should be applied annually to susceptible plants. Mulch. Susceptible
plants in hot locations should be mulched to keep soil temperatures cooler.
Avoid putting susceptible plants in intense or reflected heat areas.
Root or
Trunk Damage. Root
or trunk damage enhances iron chlorosis in susceptible plants. Mowers and line
trimmers should be kept away from trunks or stems. Plants susceptible to
damage from borers (pyracantha, fruit trees, purple leaf plum, etc.) should be protected
from borer damage. Excessive Use of
Fertilizers. Over-applying phosphorus fertilizers can
contribute to iron chlorosis. A soil test should be used to determine the
phosphorus needs of a plant. SUMMARY. Iron
chlorosis can most often be avoided by using the right plants, mulching and irrigating
correctly. The quickest method of greening up iron chlorotic leaves is with
foliar sprays of iron sulfate or iron chelates. Foliar sprays last one season
or less and may take two to three applications per season as new growth
appears. Soil applications last the longest, up to three years.
Applications should be made in late winter or early spring. When the soil pH is
unknown, use a chelated iron product.
Soil applications of iron sulfate with sulfur work to an
acceptable degree. Trunk injections should be made only when other methods can
not be used. (end of excerpt) Products containing iron that are
available in within the Desert Southwest for controlling iron chlorosis Product Iron
Source Manufacturer Use KeRex ® Chelate Organo Soil,
Foliar Ironite ® Acid.
Mine tailing Ironite Soil Super
Iron Iron
sulfate Best Soil Soil
Acidifier Chelate Green
Light Foliar,
Soil **
(top)
(top)
Soil treatments last two to three years. Iron fertilizers include iron sulfate
or iron chelates. Chelated iron modifies the ion-anion ralationship
and allows plant roots to better uptake the nutrient, even in the presence of high pH.
Acidified mining residues such
as Super Iron
®or Ironite® provide iron sulfate combined
with sulfur as a packaged product. They are inexpensive and work relatively
well. Rates of application for iron sulfate and sulfur can be found in
Table 1
(top)
(top)
(top)
(top)
(top)
(top)
(top)
w/ fertilizer®
w/ Iron®
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