Intravenal Chlorosis of Ornamental Trees

What is Chlorosis?

Chlorosis is the yellowing of leaf tissue. Yellow leaves result from a lack of chlorophyll, the green pigment responsible for making leaves green. Without chlorophyll in the leaves, the tree is unable to produce the sugars it needs to feed itself. Any reduction in the food/energy-making process during the growing season can reduce plant growth and vigor.

Interveinal chlorosis is the development of yellow leaf tissues between a network of dark green veins. Symptoms differ in this type of chlorosis, but the net effect is the same. The food making process is reduced.

Causes of Interveinal Chlorosis

The causes of interveinal chlorosis are complex and not clearly understood. Interveinal chlorosis is a diagnostic indication of a micronutrient deficiency. Complex chemical reactions govern the availability and movement of these essential mineral elements in

the soil. Iron, zinc and manganese are the most commonly deficient mineral elements that we see.

In most cases, it is not that the mineral element itself is deficient in the soil. When the soil pH is above 7.0, it is considered alkaline. High pH soils cause these mineral elements to be tied up in the soil and unavailable to the plant. Plants take up nutrients when they are in solution.

Interveinal chlorosis is known to be aggravated by cool soil temperatures, saturated soil conditions and compacted soils. Chlorosis is most severe where sub-soils are made up of native limestone or where soils are lime enriched by the addition of agricultural lime.

Susceptible tree species growing adjacent to limestone driveways and cement foundations, or have restricted root space, will also have problems. At times, other factors lead to or serve to complicate this problem. A complete soil analysis may be necessary to aid in identifying and correcting such problems.

Tree species used in eastern Iowa that are susceptible to micronutrient deficiency in high pH soils include: Pin Oak, Red Maple, Amur Maple, Silver Maple, Birch and White Pine. We are often limited in what we can do to correct the factors leading to interveinal chlorosis and at times our best efforts fail.

Control of Interveinal Chlorosis

Control of interveinal chlorosis is not easy and can be expensive. One of the best ways of avoiding this problem is to select a tree species that is tolerant of high soil pH. Diagnosing the exact cause of the chlorosis will determine the best method of treatment. Several methods are available for treating micronutrient deficiencies. Some of the methods provide short-term corrections and are quick to produce results. Others are not quick to produce results, but when the results are achieved, they are much longer lasting.

There are times when, for unexplained reasons, satisfactory results just cannot be achieved. Some soils with a very high lime content have a pH buffering capacity, making it almost impossible to lower the soil’s pH to levels that will allow micronutrient uptake.

The following are just a few of the commonly used methods for treating these micronutrient deficiencies:

• Soil application of elemental sulfur to lower the pH (slow response, longer lasting)

• Soil application of chelated mineral elements found to be deficient (relatively quick response, results sometimes variable)

• Trunk injected mineral elements (relatively quick response, can last up to 3 years)

By the time deficiency symptoms develop in the leaves, you have a substantial problem. I recommend that a combination of methods be used to treat the deficiency.

• Have the tree injected with a micronutrient blend. Arborjet Mn-jet Fe, or Mauget Inject-A-Min Iron/Zinc, for example.

• Carefully remove the sod from an approximate 100 square foot area beneath the tree while avoiding damage to the tree roots. Treat the newly exposed soil area with 5 pounds each of granular sulfur and Milorganite fertilizer. Lightly work the materials into the soil with a garden rake. Mulch the entire previously exposed area with an organic mulch such as shredded wood chips 3 to 4 inches deep. Avoid direct contact with the trunk of the tree.

• Apply EDDHA chelated iron according to label directions. (EDTA and DTPA chelated iron won’t provide the desired results in our high pH soils)

Notes

• Chelated iron, for example, should be made using the EDDHA chelating agent. It is the strongest chelate of any of the commonly used materials and maintains iron availability to plants in the pH range of 6.5 through 9.

• Milorganite is an excellent natural organic fertilizer. This complete fertilizer is non-burning, non-leaching, long lasting and provides uniform growth.

• Plants take up nutrients only when they are in solution, so make sure the area is watered in after applications are made.

• Do not use Urea as a nitrogen fertilizer. It can raise the soils pH 2 points or more. It would be better to use a fertilizer that has Ammonium Sulfate as the nitrogen source and has a low Phosphorus content.

• Do not apply Lime to your lawn without a soil test indicating it is needed.

• Do not overwater your lawn if trees are present.