Diagnosing oak wilt properly is key, as management plans and costs can be extensive, while also creating quite a stir with your neighbors. Since oak wilt is a vascular issue, it will most likely be accompanied by necrotic, foliar symptoms. Looking for foliar symptoms, along with mortality patterns indicating root graft transmission, are the most common ways to diagnose oak wilt on a property. When disease is early or not exhibiting pronounced veins as shown here, diagnostic sampling can be taken and sent to the Texas Plant Disease Diagnostic Laboratory at Texas A&M.
A majority of oak wilt infected trees will show veinal necrosis in leaves either on or beneath the tree. Knowing other recent stressors, including the weather, can help with understanding what the leaves and trees are telling you. The leaves shown here are all from one oak wilt center, showing the wide range in color and banding along with tip/margin burn, and were used in determining where active disease was on the property. Sometimes the leaves don’t show the classic symptoms, and in that case mortality patterns and sampling can be used with diagnosing oak wilt.
Red oaks can be tricky when it comes to diagnosing oak wilt as the foliar symptoms can often mimic other issues including drought or freeze damage with browning throughout the canopy. Oak wilt in red oak trees is lethal, with trees often declining within 4-6 weeks, not allowing for the use of therapeutic treatments. Most white oak species, on the other hand, are resistant to oak wilt and can often be treated as a therapeutic response to signs of stress. While live oaks develop a complex, co-dependent root system making root graft transmission almost a certainty, it’s not always guaranteed other oak species will be grafted in and affected. That being said, if it’s a “valuable” qualifying tree then preventative application may be preferred.
Knowing recent stressors, including weather conditions and other seasonal issues, can help with properly diagnosing trees. The leaves pictured are from a drought stressed live oak. This tree browned throughout its canopy while exhibiting irregular veining. Timeline of decline and inconsistencies with regards to oak wilt mortality patterns were also used in diagnosing this tree. Extreme heat from burning debris too close to healthy live oaks, as well as excessive low temperatures can create similar looks to the pictured leaves as well. Understanding symptoms and knowing a tree’s history can help diagnose properly. When there is uncertainty in diagnosis or sampling results, waiting to see signs of disease movement indicating a systemic issue like oak wilt is present may be the best course of action.
Mortality patterns are a major component in diagnosing oak wilt. Tracking disease movement can indicate that you are dealing with a systemic issue like oak wilt moving through root graft transmission. Timing of decline is also good to know as oak wilt will typically show in one tree prior to declining and being seen in neighboring trees. It will look like a slow burning fire compared to other seasonal stressors that may thin and affect a group of trees quickly, and at the same time. Decline in the originating tree will show through thinning in the canopy, with losses moving downward to lower branches. Oak wilt is often in the tree for several months prior to exhibiting the canopy loss and foliar symptoms. Live oaks will usually decline and die over a period of 4-6 months, but can often live for years stuck in a constant state of decline.
Properly diagnosing oak wilt is crucial to implementing oak wilt management plans, while minimizing undue stress to trees (and property owners) not needing treatment. Understanding how to identify where active disease is on a property will help strengthen the plans, putting the resources and efforts in the right areas. If you need help diagnosing oak wilt on your property, contact us today to schedule a consultation.
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