When thinking about oak trees, one always pictures a wide trunked gorgeous tree with sprawling branches covered with thick leaves, engulfing the ground below in a giant hug. These bewitching trees are some of the oldest that have ever existed, way before human life and thus have supported the complex ecosystem of the planet, including humans. Oak trees have over 600 different varieties all over the world and have a lifespan of about 1000 years unless affected by external factors.
Though Oak trees are expected to have the lifespan of 1000 years, this duration has been drastically reduced due to various external factors like the ever-growing commercial development, progressive changes in the environmental conditions, diseases, pests, and changing climatic conditions. While all these factors have contributed to the eventual reduction in the number of oak trees around the world, today we are going to talk about one of the deadliest diseases that is infecting oak trees in the northern hemisphere, Oak Wilt.
Oak Wilt might feel unmanageable and overwhelming when discovered. Reach out to LINY Tree Service for support services and rest assured that your trees will be nursed back to health.
Let’s dive into understanding all about Oak Wilt and its related issues.
What is Oak Wilt?
Oak Wilt is a fungal disease caused by the fungus “Bretziella fagacearum” that affects oaks trees, especially red and white oaks which are mostly seen in North America and some parts of Canada. The fungus does not necessarily kill the tree but its invasion of sapwood causes the upwards water supply to shut down and thus tricks the tree into killing itself. Though a small percentage of trees do survive after being infected, in most cases, after the initial symptoms present itself, it usually lives anywhere from 1 to 6 months. In the case of severe infection, they rapidly wilt from the top of the tree and usually die in even less time.
How does the infection spread?
There are two main ways in which Oak Wilt can spread. When ensuring the well being of the oak trees, it is important to ensure that they are safeguarded on two fronts.
- Transmission at Root Level
- Transmission overland by Insect Vectors
Transmission at Root Level
Oak trees have a tendency to grow in larger groups with intertwining roots, also known as root grafts. Thus, when one tree gets infected, there is an extremely high chance that the other oak trees within 50 to 150 meters of it might get infected too through the interconnected roots. Around 90% of all new infections are transmitted in this manner.
Transmission overland by Insect Vectors
Once the tree has been infected, fungal mats that are present below the bark of the tree produce spores continuously for a few weeks. These spores possess a fruity odor which attracts innumerable insects including the sap feeding nitidulid beetles. Nitidulid beetles are one of the top parasites that destroy plants and have been causing havoc over the years. These beetles are attracted to the mats, become carriers for the spores produced by the mats and move on to fresh wounds of uninfected trees and infect them.
What are Symptoms of Oak Wilt and it’s Diagnosis?
Oak Wilt can be easily identified in the earlier stages of infection and this can help control the deterioration process. The symptoms of Oak Wilt differs in red and white oak trees as discussed below:
Red Oak Trees
Oak wilt can be easily identified in red oaks by closely studying the leaves. The initial symptom is a subtle color shift of leaves in the upper crown of the tree. As the disease progresses, the leaves eventually turn bronze or brown from the tip to the base. The systemic discoloration of the leaves over a period of time often paves way to wilting of leaves from the top of the crown. In a matter of a few weeks, the tree is almost entirely defoliated which eventually leads to its end of life.
This phenomenon generally occurs in the months of June and July in the northern parts of the country. Unfortunately, such discoloration is very light or appears in smaller sections and thus goes unidentified by an untrained eye.
White Oak Trees
White Oak trees deteriorate one branch at a time over one to many years. Though the leaves of the white oak trees get affected in a way similar to red oak trees, the symptoms usually progress rather slowly.
How to prevent trees from getting infected by Oak Wilt?
Avoid Pruning before Wilting Prone Periods
Insects including beetles get attracted to the fruity smell of spores produced by an infected tree. These sap feeding insects then move on to uninfected trees that were wounded or pruned and lodge the spores on them, thus germinating and infecting this new host. To prevent the same, pruning should be avoided between February and June, the period when maximum insect and fungal mat activity occurs. However, this period generally differs throughout the world depending on the location and weather conditions.
If at all pruning or wounding is done during the said period, additional precautions should be taken to ensure that they don’t get infected. One of the best ways to avoid infection in such cases would be by applying a thin layer of paint that contains asphalt or has a latex base as soon as the pruning activity is completed.
An infected tree in and around the buffer zone can be treated by systemically injecting fungicides in prescribed doses into the root flares. This can be done as a preventive measure or after the roots have been infected.
How to sample the tree for further diagnosis?
How the samples are taken, handled and submitted for further diagnosis to professional labs is extremely important. If the steps are followed correctly, the chances of accurate analysis increases which in turn greatly improves the chances of recovery.
You can follow the steps below;
- Select symptomatic branches and limbs of trees, however, the highly infected parts cannot be used for testing
- Select a leaf tissue from sampled limbs, these will help in diagnosing the advancement of damage, if any. The sample of the leaf tissue and limb should be handled separately.
- Handle the samples carefully in cool packaging, without adding any water.
- Ship samples in sealed plastic bags in an ice chest.
- Results from the isolations are generally received in 2 to 3 weeks.
- Experts should be appointed to guide through the entire process to ensure that necessary actions are taken in a timely manner.
How to Treat Oak Wilt?
There are a few ways by which spreading of this disease can be stopped.
Stopping the Spread at Root Level
Oak Wilting can be stopped at the root level by creating a buffer zone around the last affected area and identifying trees then separating them from the healthy trees. A trench of around 48 to 50 meters is dug from the last symptomatic tree using commercial machinery and professional methods that cut the interconnected roots, separating the roots of the healthier trees from the affected ones, preventing the infection from spreading further.
Measures can be taken to break the root connections between dense groups of oak trees. This can be done by drilling at least 4 feet deep
If an affected tree dies, it should be burnt along with some neighbouring trees which might have been infected. These species of oak trees contain fungal mats, the spores from which can be disseminated by insects and bugs to nearby trees even after the trees die. Burning them ensures a safe passage for the trees around and acts as an end point for this infectious disease.
The fungicide is carefully injected into the oak tree’s water-conducting system by drilling tiny holes into the roots at the base of the tree. Though limited success is obtained, the success depends heavily on the existing health of the tree and injecting technique. Fungicides should be used only by trained applicators to ensure safety of the tree and get the best results.
Managing oak wilt is a long and tedious task that requires special attention. Reach out to Long Island NY Tree Service with any questions that you run into or if you want professional help. We care for your trees as much as you do and with our expertise, we will do everything in our power to ensure their well-being.