White Oak Decline

In recent years, insects, diseases, and environmental factors have led to what we call Oak Decline. These factors have a compounding effect and have led to tree decline and mortality. White and Bur oak seems to be most affected. Climate change has not been kind to our beloved oak trees!

Decline is characterized most noticeably by scattered dead twigs and branches and branches with brown dead leaves still attached in the upper crown.

Oak trees become predisposed to decline, in part because they are quite old. When older oak trees experience severe drought, and drought conditions recurring from year to year, the trees become very stressed. Once a tree becomes very stressed it becomes susceptible to opportunistic insects and disease that can ultimately kill the tree. They take advantage of a tree’s inability to manufacture the energy and defenses that are required to remain healthy. Energy is everything! Without it all life processes slowly grind to a halt.  Any condition that slows or stops the process of photosynthesis harms the tree. 

Drought isn’t the only factor causing stress for the oak trees. Other contributing factors include long periods of saturated soil conditions, soil compaction, root severance, foliar diseases, extreme heat, and insect pests.

Two-lined Chestnut Borer infestations are often first on the scene of stressed oak trees. Their possible presence is indicated by scattered dead twigs and branches which have temporarily retained dead brown leaves.

Armillaria root disease often takes place as decline progresses. Its presence can be diagnosed when dead bark at the base of the tree loosens and falls away. Beneath the bark you will see flattened black branching structures. A common name for this disease is “Shoestring Root Rot”.

When caught in the early stage of decline, management options are available to help a tree recover. Supplemental water during a drought is critical until the drought cycle is reversed. Even then, recovery will take time. Injectable insecticides labeled for the control of Two-lined Chestnut Borer are often recommended along with a tree growth regulator that will redirect a tree’s energy away from new twig growth to benefitting the trees defense mechanism and building a healthier root system.

Soil health can have a profound effect on tree health. Remediation by composting and/or mulching beneath the tree are the best long-term fix. The addition of organic matter can help balance the effects of climate extremes.

Note: White Oak Decline shouldn’t be confused with White Oak Mortality, a poorly understood but possibly connected complex appearing in SE Iowa. 

An ISA Certified Arborist will be able to accurately diagnose White Oak Decline and offer effective management guidelines.