Iron deficiency, which causes chlorosis or yellowing of the leaves of plants and trees, is found in many parts of the United States and the world.
It occurs in almost every state and South and Central America, the Caribbean Area, Europe, the British Isles, and the Middle East.
For many years, horticulturists have tried without success to find a way of controlling iron chlorosis.
Thanks to recent discoveries by Florida plant scientists, you can correct iron chlorosis in your garden orchard by applying iron chelates (kee-lates) to the soil or by spraying the foliage with a solution containing chelated iron.
Identifying Plant Iron Deficiency
You can easily tell if your plants are suffering from iron deficiency. In mild cases, the leaf veins are darker green than the areas between them.
As the deficiency becomes more pronounced, the areas between the veins become increasingly lighter green, then yellow, and finally fade to an ivory color. Unless you do something to supply iron to the plant, it will die eventually.
Two Scientists’ Discovery
Two scientists of the Florida Agricultural Experiment Stations—Drs. Ivan Stewart and C. D. Leonard of the Citrus Station at Lake Alfred—were the first to discover that chelates could supply available iron to plants in the field.
In their work with citrus trees, they found this was the only successful way to green up citrus trees affected by iron chlorosis.
Before Using Iron Chelates
Drs. Stewart and Leonard had tried several ways of feeding iron to citrus trees. They had limed acid soils heavily, applied up to 25 pounds per tree of ferrous sulfate, used sulfur and aluminum sulfate with the iron sulfate, sprayed the leaves of the trees with ferrous sulfate, and injected even solid ferrous citrate into the trunks of the trees.
None of these experiments worked. The trees remained chlorotic. But when they applied as little as 10 grams of chelated iron to the soil around each tree, the trees became green within six weeks.
New flushes of growth invariably followed the application of chelated iron around the chlorotic trees, and trees that received 20-gram applications in 1951 are still green.
Testing Iron Chelates
Dr. Philip J. Westgate of the Central Florida Experiment Station at Sanford has done several experiments to test iron chelates for vegetable crops and ornamentals.
In February 1952, he applied Fe-EDTA (Ferric potassium ethylenediaminetetraacetate, an iron chelate) to the soil around chlorotic corn plants.
The corn became green within one week, even though the soil contained a high concentration of copper which contributes to iron chlorosis.
Chlorotic gladiolus plants treated with five grams of Fe-EDTA grew within a week also, but those given as much as 25 grams were injured.
Other plants in Florida which have responded favorably to soil applications of iron chelates are:
- Chinese cabbage
- Mustard greens
- Cucumbers
- Hibiscus
- Beans
- Okra
- Azaleas
- Hydrangeas
- Ixora
- Carnations
- Camellias
- Chrysanthemums
- Gardenias
- Ligustrum
- Roses
- Snapdragons
- Spinach
- Grasses including St. Augustine, Centipede, Pangola, and Bermuda
Best Way Of Using Chelated Iron
Dr. Westgate says that chelated iron will also green iron-chlorotic plants when used as a foliar spray.
However, as little as 0.5% percent by weight of Fe-EDTA in a water solution produced severe burning on corn leaves even though it grew them.
Dr. Jay Wright of the Geigy Company in Orlando, Florida, has found that as little as one pound of Sequestrene NAFe (an iron chelate produced by his company) in 100 gallons of water produced some burning rose leaves. However, he got good results with 15 pounds per acre added to the soil without burning the plants.
Dr. Westgate advises that, at present, soil applications seem to be the best way of using chelated iron to correct iron chlorosis.
For Home Garden Use
A safe rate of application would be 1 ounce in 25 gallons of water per 100 square feet or 1/4 teaspoon per gallon per square yard.
Iron chelates themselves are not new. The first use of chelating agents was in the laboratory in analytical chemistry.
EDTA is a chelating compound that is used widely in industry, but the Florida experiments were the first ones to use chelates to supply iron to plants in the field.
Chelates were used in solution cultures in the greenhouse sometime before they were used in the field.
Importance Of Chelates
The word chelate comes from the Greek word meaning claw. Therefore, chelates may be compared to two claws that catch and hold metal ions.
Metal is then free to be taken and used by plants and does not combine with other elements to form insoluble compounds. Unfortunately, iron often does this in simple iron compounds and becomes unusable by plants.
Because of this tendency of iron to form insoluble compounds, plants are often iron chlorotic even when there is plenty of iron in the soil for normal growth.
This ability of chelates to hold metals, particularly iron, in a form plants can use gives chelates their importance.
Treating With Iron Chelates
Iron chelates are already being used extensively in Florida’s citrus, commercial trucking, and flower-growing areas.
Much of the vegetable land around Sanford, a rich vegetable-growing area, show symptoms of iron chlorosis. Dr. Westgate reports that much of this iron-deficient land now produces good crops after being treated with iron chelates.
For example, one grower lost a vegetable crop on a 50-acre field. Then he treated the field with seven tons of chelated iron (one percent). The crop before treatment had to be plowed under as a complete loss, but the treated crop made a good yield.
Where Iron Chelates Do Not Work
Iron chelates available now do not work as well in soils with a high pH as in more acid soils.
At this time, scientists are trying to find other chelated iron compounds that will be available under alkaline soil conditions.
Image/s: (Page 37)
The two gladiolus plants above were both treated for iron deficiency at the same time. The plant, left, sprayed with iron sulfate, did not improve. Healthy plants, right, resulted when chelated iron was applied to the soil
Azalea plant photographed before treatment with chelated iron. The same plant (right), its healthy green color restored, was photographed six weeks after chelates were applied.
44659 by William G. Mitchell