What is Oak Decline?

Oak Decline is a debilitating and often deadly condition affecting our Bur Oak trees. Bur Oaks are extremely sensitive to small changes to their growing environment and are often placed under great stress, or die from grade changes, compaction of soil around the root zone, acute injury from construction or changes to the soil air to moisture ratio.

Since 1986, Bur Oak trees in southern Manitoba have experienced environmentally related stress and dieback leading to considerable damage to landscape, ornamental, and natural stand groupings.

Drought greatly weakens and stresses oaks, causing them to be more vulnerable to insect and disease problems.

Typically, on stressed Oaks, tree foliage wilts from the top downward, turns brown and normally remains persistent on the branches. Initial decline due to stress starts a cycle of further deterioration involving the two-lined chestnut borer, Agrilus bilineatus (Weber) which gains importance in the cycle as the decline progresses. The Two-Lined Chestnut Borer is considered a secondary insect, affecting stressed Oaks.

Prevention

Carefully watch your new tree. Monitor for signs of poor health such as leaf yellowing or leaf drop and insect infestations. In most cases, the tree will be strong enough to overcome small problems on its own, as long as it is provided sufficient water, especially during periods of drought.

Maintenance

• Maintain oak trees in a healthy condition through a comprehensive watering program during periods of dry weather and general tree maintenance which includes removal of dead wood by proper pruning methods.

Protection

• Protect the base and root systems of oaks and surrounding area during construction. This will prevent root damage. Avoid soil compaction around the Oak. Do not excavate the upper surface soil for asphalt, paving, sprinklers, etc damaging the sensitive oak roots.

Fertilization

• Fertilizing with a fertilizer high in phosphorous during or immediately after drought periods, will assist in promoting and stimulating feeder root growth. This is specifically important if the dry period has caused the fine fibrous root system to die back.