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Horned Oak Gall - Tree Diseases

Louisville Tree Service Blog


Horned Oak Gall

Known to occur from southern Canada to Georgia, Horned Oak Gall is abnormal tissue growth that is infected by wasp eggs on Pin, Shingle, Laurel and/or Willow Oaks. Most types of gall are only aesthetically unpleasant and are no risk to the health of the tree. However, Horned Oak Gall are unsightly and have the potential to kill a heavily infested tree by reducing vigor and opening up the tree to secondary attacks from other insects and diseases.

About The Horned Oak Gall

Galls occur when in the spring, when tiny wasps lay their eggs on the leaves, causing small blister like bubbles. The second generation lay eggs in the summer, in the buds of the twigs, which eventually cause woody masses. The woody masses are where the wasp eggs are held. The woody masses, or galls, girdle the branches and act as parasites stealing food, nutrients and energy from the tree. Since each gall can hold up to 200 eggs the damage can be quite rapid and devastating to the tree. These galls can grow more than 2 inches in diameter and take two to three years to fully develop. During the egg-laying process and early larval feeding period, specialized body glands secrete growth regulating chemicals that interact with certain plant chemicals to produce these abnormal growths/galls. Once a gall begins to develop it is impossible to stop or reverse its development.

Stages of Horned Oak Gall

Stages Of Development

  • STAGE 1- initially the gall looks like blisters on the foliage.
  • STAGE 2 - male and female wasps emerge, mate, and then the female wasp lays eggs in the buds of the twigs.
  • STAGE 3 - in two to three years the gall becomes mature and a female wasp will emerge to restart the cycle.

The galls have much durability when it comes to self-preservation. They provide complete protection from natural enemies and also from insecticide treatments. Unless registered insecticides are applied, when gall wasps are still flying about, they offer little or no effective measure of control.


At Louisville Tree Service, LLC If the tree is lightly infested with oak gall, we prune the infested branches to reduce the problem and prolong the life of the tree. We often use a basal root flare and soil injection for a minimum of three consecutive years, which can be used as a preventative to break the life cycle. Around mid-April, while the galls are small and have yet to develop, we inject the soil, prune and destroy the infested plant material. This takes place before early May since that is when the pests emerge. If you would like to know more about this process and our other services, please contact us with any questions.

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