Iron chlorosis in trees and shrubs

Farm Forum

What is iron chlorosis in trees and shrubs and what causes it? Many of our soils have a high pH and iron unavailable causing a yellowing of leaves from iron deficiency. Usually the leaves are yellow with dark green veins but in severe cases, even the veins may turn yellow, or leaf edges may scorch and turn brown. Some of the trees most susceptible are Silver maple trees, Norway maples and other maples.

If a tree is young and constantly chlorotic consider removing it and planting a better-adapted species. But what should be done about large, established, valuable trees that are exhibiting chlorosis symptoms?

Several methods are available for treating iron deficiency as follows: 1) soil application of elemental sulfur combined with ferrous sulfate; 2) soil application of iron chelates; 3) foliar sprays containing ferrous sulfate or chelated iron; or 4) trunk injection of ferric ammonium citrate or iron sulfate. Often, one method will work well in one area but not in another due to variations in soil conditions and species susceptibility.

· Soil treatment – Use soil applications to treat individual trees and shrubs, in the fall or early spring. A mixture of equal parts iron sulfate and elemental sulfur can produce lasting results and is relatively inexpensive. Treat small areas by making holes 1 to 2 inches in diameter, 12 to 18 inches deep and 18 to 24 inches apart under the tree. Make holes with an auger or soil probe that removes soil. Avoid damaging large, woody roots when making holes. Also, check with local utility companies if making holes in the vicinity of underground utility lines. Fill each hole with the iron sulfate-elemental sulfur mixture to within 4 inches of the soil surface.

Areas of small shrubs in a garden also can be treated with equal parts ferrous sulfate and elemental sulfur. Use a hoe to excavate a small trench approximately 4 inches deep, 12 to 24 inches away from the base of plants. Apply one inch of the ferrous sulfate-elemental sulfur combination to the bottom of the trench and then fill in the remainder of the trench with soil.

Over time, the concentrated sulfur in the holes or trenches reacts with precipitation to form acid which lowers soil pH. One soil treatment may last 2 to 4 years depending on conditions.

· Foliar treatment – Foliar applications are made directly on the leaves of affected plants during the growing season. These treatments produce a quick response but control is spotty and temporary. Foliar sprays are difficult to apply to

large trees.

· Trunk injection or implantation – Injection treatments generally are most effective if applied in the early spring during bud break. Iron compounds in dry or liquid form can be placed directly into holes drilled into a tree’s lower trunk. Studies have shown that uptake is better and more evenly distributed if holes are drilled near the soil surface on the outside of root flares.

My source for this news article was Utah State University Extension. If you would like more information about “Iron Chlorosis in Trees and Shrubs” call Bob Drown at the Conservation Office at 605-244-5222, Extension 4 or by e-mail at