Archive for Sunday, July 22, 2001

Iron-poor trees need assistance

July 22, 2001


Mature trees are an important part of any home landscape. Keeping them healthy can be a challenge in the summer heat.

A physiological condition known as iron chlorosis is not making it any easier. Caused by a lack of iron, chlorosis causes leaves to turn pale green to yellow while the veins remain a deep green color.

Iron is an important building block for chlorophyl, the chemical substance that makes leaves green. However, when trees are stressed by root damage, high soil pH or other conditions, they are not always able to use the iron that is in the soil. The result is iron chlorosis.

Showing up mostly in pin oaks and sweetgum trees, it also can be a problem in silver maple, bald cypress, crab apple, white pine, elm, London plane tree, cottonwood, walnut, sugar maple, Eastern red cedar, Bradford pear and willow.

In severe cases, leaf color may change from yellow to white to brown. If uncorrected, twigs and eventually whole branches can die. Affected leaves may be found over the entire tree, on one side only or be limited to individual branches.

Correcting iron chlorosis begins with adding iron to the plant by leaf application, soil treatment or trunk injection.

Leaf application will give the fastest response but is short-lived. A spray with iron sulfate or iron chelate solution can be applied when the tree is in full leaf.

Although a leaf spray produces quick results, the improvement is temporary because iron will not move into the tree beyond the sprayed tissue. New growth emerging after treatment will be chlorotic.

Soil treatments yield long-term results. The goal is to add iron to the soil to increase the amount available to tree roots. In bare soils, iron sulfate can be applied to the ground under the tree canopy at a rate of one pound per half inch of trunk diameter measured at chest height.

Trees growing in turf-covered soil should be fed either by liquid injection with a deep-root feeder or by iron sulfate placed in holes drilled into the soil.

The most common method of correction is by trunk injection. Iron sulfate, iron citrate or iron chelate injected or implanted directly into the tree trunk is a fast and long-term way to control iron chlorosis.

Trunk injection systems available to homeowners include Medi-Caps and NutriBooster. Small holes are drilled in the tree for cartridges. When implanted in the tree trunk properly, cartridges release nutrients into the water transport system.

A response can usually be seen in two to three weeks. Additional injections will not be needed for three to five years.

By applying iron, the tree will green up and grow for several years. For the long term, however, it's better to evaluate the soil and plant trees that are not influenced by higher pH or droughtlike conditions.

Bruce Chladny is horticulture agent at K-State Research and Extension-Douglas County. For more information, call him at 843-7058 from 8 a.m. to 5 p.m. weekdays.

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