What is Oak Gall & Why is My Pin Oak Tree Declining?
Oak Galls are abnormal outgrowths on the external tissue of trees. In the case of Oak Gall, this abnormal growth is a response to a Pest Infestation. Various species of wasps lay their eggs in the new bud growth of a tree. The larvae then secrete chemicals that induce the tree to form these galls. The larvae then use this gall as a home (food and protection from enemies and the tree's defenses) for part of their life cycle. These cynipid gall wasps have an “alternating generations” biology, meaning that in early spring the wasps emerge from the woody stem galls and the females oviposit in the emerging leaf growth of the host tree. The eggs hatch 1-2 weeks later and the galls begin to form on the newly forming leaves. Adult wasps emerge from the galls 2-3 months later, and members of that “leaf generation” begin to oviposit in the tree's new shoot growth. The developing wasps in the stem (or woody galls) may take 2-3 years to develop and then emerge to start the process again.
This mature Pin Oak Tree located in St. Peters, MO is suffering from Gouty Oak Gall.
Identifying Oak Galls on Pin Oak Trees
Oak Gall (whether Horned or Gouty) in the St. Louis area, will affect mainly Pin Oak Trees (Quiercus palastris). Galls or abnormal growth will appear on leaves, branches, and twigs. The gall resembles a small, round, and woody structure with either lumps or horns protruding from it. Think about a tumorous growth
History of Oak Gall in the Midwest
Oak Gall has been a persistent phenomenon in the Midwest since its first confirmed cases in the early 20th century. Specifically, Horned Oak Gall and Gouty Oak Gall (caused by two closely related species of wasps) have been observed throughout the Midwest. Originating from the eastern United States, these cynipid gall wasps have spread across the region, particularly affecting urban and suburban landscapes where Pin Oak trees are commonly planted.
What is the impact of Oak Galls?
Oak Gall Infestations can cause varying degrees of stress to its host tree. Oak Gall can cause more significant damage to trees than other types of galling insects due to the size of the growths and life cycle of the pest. A heavy infestation can lead to:
· Reduced Photosynthesis: Leaf damage and reduction prohibit the tree’s ability to photosynthesize (produce and store energy) leading to stunted growth and depleted food/energy storage.
· Vascular Restriction and Dieback: The abnormal growth blocks the vascular tissue of the tree, reducing its ability to push water and nutrients to the furthest tips of the tree. This can affect the vital functions of the tree such as respiration, transpiration, temperature regulation, photosynthesis, and defensive hormonal processes.
· Increased Pathogen Susceptibility: Infested trees with existing pest pressure can become more vulnerable to other biotic and abiotic pathogens/stressors. Things like fungal pathogens, additional pests, and increased vulnerability from surrounding environmental factors.
· Aesthetic Damage: Galls mar the beautiful appearance of your trees, often impacting the vigor, vitality, and growth habits of your tree.
· Hazardous Limb Loss: The added weight of numerous galls can cause limbs to break and fall becoming a risk to people and property in the target zone.
· Eventual Death of the Tree: If left untreated, severe infestations can push the tree into a mortality spiral.
What Should I Do with My Infested Tree?
Managing your trees can be a daunting task. You may find conflicting recommendations for treatment, worry about investing money into a mature or old tree only to have it succumb to another issue, or feel like you don’t have enough information to make an informed decision.
We recommend that you start by having an ISA Certified Arborist assess your tree and discuss any concerns or recommendations they might have for any tree on your property that you want to manage. Your local ISA Certified Arborist will be able to identify any issues or concerns with the health and safety of your trees. They are uniquely suited to make recommendations based on a residential tree management perspective. Where large institutions may prioritize the overall plant ecology of a large region, forest, or park, your local ISA Certified Arborist will be able to make recommendations that align with the priorities of a single homeowner with limited species and plant ecologies.
Treatment Options for Oak Gall Infestations
· Prevention is Always better than reactive treatment: Regular inspection and monitoring can help detect many issues or stressors at their earliest stages. Proper tree management such as watering, mulching, and fertilization will increase your tree's health and resilience. Regular pruning to remove dead or weak branches can reduce the chances of infestations.
· Plant Healthcare Treatments: for infested trees or trees in proximity to affected trees the application of chemical insecticides can prevent infestations or alleviate current infestations. Our preferred Chemical treatment is a systemic injection of insecticide into the host tree that kills the offending wasps and a growth regulator injected into the root zone of the tree which minimizes the new bud growth, reducing the number of sites the wasps have to lay new eggs. Our treatment plan recommends a treatment every 2 years for a period of 6 years to adequately disrupt the life cycle of the wasp.
Why Choose Provision Arbor Care to Manage My Oak Gall Infestation?
At Provision Arbor Care, we prioritized staying up to date on the latest science in the Arboriculture industry. We know St. Louis well and are trusted by thousands of local customers to evaluate, recommend, and treat their trees. This experience allows us to keep a finger on the pulse of Arboriculture in the area. Our team of ISA Certified Arborists provides the highest quality care for your trees. Whether you are dealing with an Oak Gall infestation or any other tree-related issue we have the knowledge, experience, and tools to ensure your trees thrive.
