Oak Wilt in NW Ohio

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This summer, there have been several phone calls to the Extension office in Lucas County from concerned residents describing red oak trees declining quickly.  Many described their tree(s) exhibiting symptoms that one could suspect that oak wilt (Ceratocystis fagacearum) might be the cause.  The symptoms described included:  flagging of branches in the tree's canopy; withering of leaves that turn brown and ultimately drop before normal seasonal leaf drop; and rapid decline of the overall canopy - some describe it as happening "overnight".  Additionally, sapwood streaking and fungal mats may be present, but sometimes are not always obvious or evident.  Because of this, conclusive diagnosis can only be made in specialized laboratories, such as The Ohio State University C. Wayne Ellett Plant & Pest Diagnostic Clinic (ppdc.osu.edu).


If you suspect oak wilt, the quality of sample that you submit to the lab for confirmation is key.  Selected branches should be partially wilted or in-transition, with symptomatic leaves progressing from the tip of branches inward to the trunk.  Branches that are totally wilted, dry, or dead should be avoided as they will not be viable and could give a false negative.  


Ideally, the branch samples should be at least 1" in diameter and cut into 6" - 8" lengths.  Smaller diameter branch samples can be acceptable but only if the sapwood is very moist, and samples have been kept cool until they arrive at the lab.  Samples should be overnighted early or mid-week, or hand delivered to the lab as soon as samples are collected in the field.  It is important that collected samples don't ride around in a vehicle, especially when it is warm, allowing them to dry out quickly.   


The collection of samples from a mature suspect tree usually require the assistance of an arborist who can either climb the tree or utilize a bucket truck to gain access to the perfect samples to be submitted to the lab. 


Additional details on collecting field samples are described in this USDA Forest Service publication, How to Collect Field Samples and Identify the Oak Wilt in the Laboratory.  The publication is available online at:  https://www.na.fs.fed.us/spfo/pubs/howtos/ht_oaklab/toc.htm


If the tree tests positive for oak wilt, management of this disease should include prevention of further overland and underground spread to nearby oaks, proper disposal of infected tree(s), and possible proactive protection of highly valuable trees in the immediate area with a label fungicide.   


It is important to note that not all brown leaves on an oak tree, especially red oaks, are a result of oak wilt.  Drought, change in grade, or injury to the tree's root system, truck or branches, can result in brown leaves, branch dieback and canopy decline.  This is why it is important to submit samples to the lab for confirmation. 


Additional information about oak wilt can be found in the Oak Wilt in Ohio Factsheet authored by Pierluigi (Enrico) Bonello, with OSU's Department of Plant Pathology.  The FactSheet is available online at http://ohioline.osu.edu/factsheet/plpath-tree-02