A lot of what I have to say here is aimed at the challenges of diagnosing oak wilt. But, be patient, at the end I’ll tell you the best way to get the answer you need. According to research, diagnosis is the main factor that causes problems with management plans (Appel 1994). Let me tell you, my experiences out in the field completely backs up this research. It may seem obvious to you that diagnosis is important, and why would that be causing such a big problem with oak wilt strategies? There are a few interesting points on this subject I’d like to spell out for you.
The same symptoms of oak wilt are caused by many other tree disorders. To understand this you need to realize that the words “symptom” and “diagnosis” don’t mean the same thing. I could write a whole article on the relationship of symptom and diagnosis, but we’re talking about oak wilt here. As an example, if you look at the Texas Forest Service oak wilt site (http://texasoakwilt.org) you will see that one symptom of oak wilt is vein banding. Here is a short list of other tree disorders that also display vein banding: chlorosis, herbicide damage, root damage, transplant shock. There are more. If you do go to the website I mentioned before you’ll see that there are several other leaf symptoms that you might find on an oak wilt site. All of these other symptoms can also be caused by many things other than oak wilt.
Our understanding of this disease is in its infancy. Up until the 80’s we didn’t even realize that oak wilt was the disease killing our native treasures (thank you Lewis & Oliveria 1979). We were aware of oak wilt before then, but didn’t know it was responsible for so many of our problems. It wasn’t until 1994 that a proper management plan was developed by a qualified pathologist (Appel 1994).
The best weapon we have to positively identify oak wilt is by observing a pattern of spread. Here is an excerpt from Appel’s research paper:
A five step diagnostic protocol is recommended for routine tree diagnostics in central Texas. Although designed to distinguish oak wilt from other diseases, the protocol has proven useful in diagnosing any tree problem. The completion of all five steps is unnecessary to make an accurate diagnosis and may be impossible. The five steps are: 1) observe the pattern of dieback and mortality in time and space for the tree population, 2) observe the patterns of dieback and mortality in time and space for individual tree crowns, 3) examine specific organs, e.g. leaves, branches, or roots, for unique patterns of chlorosis and/or necrosis (symptoms), 4) examine specific organs for evidence of the pathogen (signs), and 5) attempt to obtain laboratory isolation of suspected pathogens.”
There is one part of this excerpt I would like to draw special attention to, “observe the pattern of dieback…in time and space.” In my experience this is the most overlooked part of the diagnostic process. Any potential oak wilt site needs to be monitored over a period of time. I’m not talking about a week or a month. A good arborist, who is capable of diagnosing all tree disorders not just oak wilt, needs to visit the site about 4 times over the course of a year. I can’t tell you how many times I show up to meet with a potential client and they have already been told they have oak wilt by 3 different people who have just seen the site for the first time. I think this is unreasonable and irresponsible, and is an obvious breech of the recommended protocol.
Ideally photographic evidence should be taken. A picture is worth a thousand words. It’s easy to get into a conundrum over what the tree really looked like a year ago when you are trying to go by memory. In today’s digital photography world, it is so easy to do there is no reason not to.
I can’t even begin to count the number of times I’ve been called to a property for the purpose of providing a price for oak wilt treatments, and there was obviously no oak wilt on site.