For Release July 3, 2001

AGRI-VIEWS
by Chuck Otte, Geary County Extension Agent

Iron is a simple compound. It’s also very common. In chemistry class, we learned that it is represented by the letters Fe. Its atomic number is 26, which has something to do with the positive charges on the nucleus. Its atomic weight is 55.84 which means it’s heavier than most of the gaseous elements but slightly lighter than things like copper and zinc.

Both plants and animals need iron in very small amounts. In people, iron is needed for certain enzymes and is critical for the formation of hemoglobin in the blood. We don’t need a lot of iron, but if you are deficient (anemic) you aren’t going to function very well for very long! Plants need iron too. Plants use iron for certain enzymes, for reactions in the plant’s respiration and as a critical component of chlorophyll. Chlorophyll is what makes leaves green, and is vital in photosynthesis, which is the life of the plant.

When plants are short of iron they become sick too. We call the condition iron chlorosis which you can consider the same thing as being anemic. When plants become chlorotic it doesn’t take very much iron to fix the problem. In field crops, we may be talking about rates of only three to five pounds per acre. So the break between a plant being okay and being chlorotic is a very fine line.

The first symptoms of iron chlorosis is the failure of the plant to develop a normal deep green color in the foliage. You need to compare leaves of the same species since different plants have different normal green color levels. Deficiency of other nutrients can also cause a pale appearance, so you have to look a little deeper.

We most frequently see iron chlorosis in trees. The leaves fail to develop a full green color and the veins in the leaves are often much darker than the surrounding tissue. As the condition worsens, the leaves will often become smaller. Chlorotic leaves are also very prone to scorching in hot summer weather. Scorching, as its name sounds, is dying of leaf tissues usually at the edge of the leaf, but sometimes spots in between the veins as well.

As chlorosis continues to worsen, limbs start to die from the tips back to the trunk. If not treated, a tree will die after several years of iron chlorosis. Iron is known as an immobile element in a plant. The plant can not move it from surplus areas to deficient areas. A tree can develop chlorosis on just one limb or one side, but nowhere else in the tree.

The plot thickens further. In many cases, simply adding iron to the soil will not help. Iron becomes tied up in soils with a pH above 7 (alkaline soils). The alkalinity causes the iron to become tied up in the soil in plant unavailable compounds. Different plants react differently and different weather conditions can create problems for plants. We know that pin oaks, sweet gums, and maples are the most likely tree species to show chlorosis.

Various treatment methods are available. In severe cases we use special equipment to inject iron solutions directly into the tree. Homeowners can treat mild cases with soil acidifying compounds like sulfur or aluminum sulfate. You can also use a general fertilizer that is high in iron and sulfur and place it into holes in the ground around the drip line of the tree. The sulfur lowers the soil pH which makes the iron more available to the plant.

Iron is essential to plants and animals alike. If either is deficient, the health will suffer and long term deficiencies can be fatal. For more information on this subject, stop by the Extension Office at 119 East 9th, and ask for the bulletin, Iron Chlorosis in Trees.

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