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Pin Oak Chlorosis
Need to know:
- Symptoms include yellowing of leaves with dark green veins, angular brown spots, and brown curled leaf margins.
- Pin oak chlorosis occurs in soil with high pH because of the inability to absorb iron.
- Treatments include foliar application, soil application, and trunk injection.
Overview of pin oak chlorosis
Pin Oak (Quercus palustris) does poorly on Iowa's clay-rich, poorly-drained soils. When planted in soils with a pH greater than 7.5, the pin oak develops iron chlorosis, a nutrient deficiency symptom. (Other tree species are also susceptible including silver maple, bald cypress, crabapple, and sweet gum.) Affected trees have yellow leaves with dark green veins, with some developing angular brown spots and brown, curled leaf margins. In severe cases, leaf color may change from yellow to white to brown. After suffering from chlorosis for several years, branches and twigs may begin to die. Chlorosis is often most severe in areas where topsoil has been removed, exposing clay subsoil, as in new housing developments.
Usually, there is plenty of iron in the soil, but high soil pH prevents the iron from being absorbed by the plant. Since iron is essential for the production of chlorophyll, the tree fails to produce enough chlorophyll to maintain healthy green leaves. Lack of available iron can be magnified by low soil temperatures; high soil moisture; large amounts of copper, manganese, or zinc; or excessive application of phosphorus.
Symptoms of pin oak chlorosis
Yellowing of leaves can vary from a yellowish-green color in slightly afflicted leaves to a bright lemon yellow or even white in severely affected trees. Interveinal areas see the greatest change in color while the veins of the leaves may remain green. After longer periods of time brown necrotic areas may begin to form on the edge of the leaf. Should the tree be affected by chlorosis for multiple years, shoot growth will be reduced and dieback in foliage will occur. This can lead to eventual death of a tree.
Signs of pin oak chlorosis
Chlorosis is usually caused by a deficiency of iron available for the tree to use because the soil pH is too high so no biotic signs will be seen.
Type of Sample Needed for Diagnosis and Confirmation
The Iowa State University Plant & Insect Diagnostic Clinic can help you to investigate and confirm if your plant has a disease. Please see our website for current forms, fees, and instructions on collecting and packing samples. Contact information for each state's diagnostic laboratory for U.S. residents can be located on the NPDN website. If you have a sample from outside of Iowa, please DO NOT submit it to the Plant & Insect Diagnostic Clinic without contacting us.
Management of Pin Oak Chlorosis
Although beautiful under the right conditions, the pin oak is not a widely recommended tree to be planted in Iowa. Choosing plants more suitable for your soil will reduce disappointment and many headaches in the future. The best way to avoid this problem is to not plant pin oak at all.
There are several attractive oaks that do much better in typical Iowa soils. Recommended species include chinkapin oak (Q. muehlenbergii), English oak (Q. robur, cultivars 'Fastigiata' or 'Wandell'), or red oak (Q. rubra). Below are some common shade trees found in Iowa and their preferred soil pH ranges.
Preference of certain species of trees for various soil pH levels
|pH 5.5 or below
|pH 5.0 to 6.5
|pH 6.0 to 7.5
|Tulip tree (Yellow poplar)
Source: Nebraska Cooperative Extension Service
If however, you have a yard with an established pin oak, there are three methods in which iron chlorosis can be treated due to an alkaline soil situation, though they can be expensive and/or time-consuming.
While foliar application of iron sulfate or iron chelate can provide a quick response, the remedy is temporary since the iron does not move beyond the actual leaves that are treated. A rate of five pounds of iron sulfate in 100 gallons of water (2.5 oz. iron sulfate in 3 gallons) is recommended. Adding a tablespoon of detergent to the mixture will help to wet the foliage. Iron chelates are water-soluble forms of iron that remain in solution, therefore available to the tree. It is best to apply foliar applications during the evening or during periods of cool weather.
Soil Applications and Amendments
Adding iron chelates or acid drenches to the soil can make iron more available to the tree for two to three years, but won't have a lasting effect on soil pH. Iron sulfate or a mixture of sulfur and iron sulfate can be used to make iron more available to the tree roots. Treatments are typically applied by drilling holes spaced two feet apart and 15 to 18 inches deep in concentric circles around the tree, extending beyond the dripline by about 3 feet. Common chelates available at garden centers include the trade names "Tru-Green" and "Sequestrane." Consult the labels for rates.
Homeowners can also try to lower the soil pH by applying elemental sulfur (96%) at the rate of 2 lbs/100 square feet in April and again in September.
Tree injection systems include some available to the homeowner and others available only to professional tree services. Home injection systems include Medi-Caps and NutriBooster.In this treatment, iron sulfate, iron citrate, or iron chelate is implanted in 3/8" holes 1/2" to 1" deep drilled in the tree trunk and then sealed with paraffin or grafting wax. Another method uses liquid ferric ammonium citrate applied in drilled holes or through a reservoir system. Injection treatments are most effective if applied in the early spring during bud break. However, homeowners should weigh the potential benefits from trunk injection with the potentially negative consequences caused by wounding the tree. This treatment should be reserved for high-value trees.
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