Healthy pin oak tree losing brown leaves this time of year. It doesn't appear...

Asked July 14, 2014, 10:20 AM EDT

Healthy pin oak tree losing brown leaves this time of year. It doesn't appear to be dying, just losing some brown leaves. Is this ok???

Macoupin County Illinois

1 Response

Pin oak trees (Quercus palustris) are extremely susceptible to iron chlorosis in high pH and limestone soils. Chlorosis in pin oaks is usually due to a deficiency of iron in the leaves. Iron is important for chlorophyll synthesis in plants, so when it is deficient, leaves cannot make chlorophyll, resulting in a yellow appearance and eventually turning brown. Chlorosis of pin oaks is typically associated with alkaline soil pH – pH greater than 7. As soil pH increases, the ability of pin oaks to take up iron decreases dramatically.

The best solution for iron chlorosis is to avoid planting pin oak in alkaline soils. You may consider a soil test to determine the severity of the soil alkalinity.

There are four principle treatments for chlorotic pin oaks:

1) Soil application of iron sulfate or sulfur

The objective of these applications is to lower the soil pH and increase iron availability. It is important to remember that the underlying problem is usually not the amount of iron in the soil, but the amount that is available to the plant. Therefore, the advantage of this approach is by lowering soil pH, it addresses the basic problem.

2) Soil application of chelated iron

The objective of this approach is to apply iron in a form that is readily taken up by trees. Application of iron chelates can produce greening within a couple weeks. The disadvantage is the effect can be short-lived and can be relatively expensive.

3) Foliar sprays

Iron sulfate or iron chelates can be applied to trees as a foliar spray. This can often provide a rapid green-up within days or a week. Some leaf burn is also possible, however. The treatment does not address the underlying cause and the effect may only persist for a year.

4) Trunk injection

Professional arborist can apply iron to trees via trunk injection. This enables treatment of trees that are too large to effectively apply a foliar spray. Trunk injection can also provide a rapid green-up often within a week. Again, the treatment does not address the basic problem of alkaline soils and usually needs to be re-applied every couple years.

Also, regular maintenance of mulching with wood chips and watering during drought periods is always a good idea.

For more specific help, you can contact your local Master Gardeners at:

University of Illinois Extension
Macoupin County
#60 Carlinville Plaza
Carlinville, IL 62626
Phone: 217-854-9604