HELP--The Leaves on My Trees are Turning Yellow!!!!

Gail Ruhl, Senior Plant Disease Diagnostician, Interim P&PDL Director, Botany & Plant Pathology

The diagnostic lab has received numerous samples and phone calls regarding yellowing of foliage on a variety of trees, including pin oak, red maple, sweet gum and riverbirch. 

Yellowing of foliage (chlorosis) is due to a lack of chlorophyll development.  Compacted soils, poor drainage, alkaline soils, nutrient deficiencies, and root damage are among the factors that can induce chlorosis in woody plants.

Pin oak, riverbirch and red maple are sensitive to soil conditions such as high pH, which ties up manganese and iron as well as other minor elements, making them unavailable to the roots. Poorly drained or compacted soil can also have these effects by resulting in poor root growth and inability to take up these minor elements. This problem often occurs under the stressful conditions of summer when roots are unable to take up enough manganese or iron to support continuing growth.

What to do? Recommendations vary. Pin Oak and Riverbirch often exhibit classic symptoms of iron deficiency while Red Maple often exhibits classic symptoms of manganese deficiency. Some suggest spraying the foliage with a mixture of iron and manganese sulfates or chelates (1 1/2 tablespoons each per gallon of water). This should correct the problem in a week or so, but unfortunately it is temporary in effect. Applying the two minor elements to separate branches will allow you to determine which one or perhaps both are the problem. The following extension publications provide more details on approaches to this problem which involve correcting poor drainage or high pH, and the application of minor elements by several techniques:

Iron Chlorosis of Trees and Shrubs - Purdue University Extension

Iron Chlorosis Of Woody Plants: Cause And Control - University of Illinois Extension (pdf file)

Focus on Plant Diseases: Chlorosis - University of Illinois Extension

Preventing and Treating Iron Chlorosis in Trees and Shrubs - Utah State University

Iron Chlorosis in Trees - Kansas State University Extension

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Information listed is valid only for the state of Indiana.