FRST 351 - Forest Pathology

Identification - Diagnostics

Note, black text relates to identification and blue text relates to diagnostics.

Background

When you notice something wrong with a tree (i.e. it "looks diseased somehow") it is important to determine the cause if you wish to manage the situation.  If you see a part of the pathogen (i.e. the fruiting body, mushroom, aerial shoot, mycelium, etc.) you should hopefully be able to positively identify it.  And if there is a sign that you do not recognize, you can send it off to the experts to identify.  Please note the message here ... you ID something based on a sign (physical part of the pest).

If you do know all of the significant pathogens (and insect pests) of forest trees in BC, then you should be able to identify the causal agent ... maybe only half the time ... likely less.  Why not all the time you ask?  Well ...

1. although there are symptoms, often there are no telltale signs (physical part of the agent) detected ... no signs - no ID

2. environmental agents (heat, cold, drought, etc.) usually do not leave 'calling cards' ... no signs - no ID

Given this situation, how do we determine the casual agent?  This is akin to you feeling ill and going to the doctor to find out 'what you have'.  The doctor looks you over, observing bags under the eyes, a yellow pallor, and asks questions like "what hurts? how does it hurt?".  The doctor is gathering clues, and based on this collection of symptoms, will attempt to diagnose the cause of your ailment.  Diagnosis is a process of examining pertinent information in order to determine the cause.  The TV show House is a classic example of diagnosis in action.

Stated Course Objective:

Someone who passes this course should:

1. Be able to identify pathogens based on signs.  For example, if you are given a sample or image of a pathogen (conk, aerial shoot, mycelial fan, etc.), you should be able to positively ID the culprit.

2. Be able to diagnose the most likely causal agent if there are NO signs present.  In the absence of definitive signs, you examine the collection of symptoms (i.e. you ask the tree "what hurts and how does it hurt?").

3. Be able to discuss the difference between identification and diagnosis.

Preparing for the ID Exam

In order to be able to ID pathogens you should have taken time during term

1) to examine the samples in the class and

2) examine images in books (especially the green handbook) and on the web (Tree Doctor - the Images page has a great collection of photos that were acquired from the Ministry of Forests, Canadian Forest Service and academics).

Let's Play House

(or Let's Play Doctor ... although I used to get in trouble for that when I was a kid)

Being able to diagnose a pest problem can be challenging.  Especially for someone just starting out.  Unfortunately the dianostics section has (temporarily) stopped working - no idea why :(  Luckily there is something that can help you ... yes it is the Tree Doctor.  Use the Diagnostics page and play around.  I would suggest

1. first, eliminate all candidates except for disease (we don't know our bugs yet) - click the Select Pest Category drop-down and click Disease - note that the list now only includes diseases

2. second, pick a tree - this will shorten the disease list to only those that beat the crap out of infect that tree - e.g. pick Lodgepole Pine

3. next, click on the first sign/symptom ("reduced leader..") - note that the diseases that match the selected S&S all have light pink shading, meaning they match all the S&S selected thus far, but there is no "lead contender yet"

4. hold CTRL and click "thinning foliage.." - note the change - Black Stain was added to the list - but still "no lead contender"

5. hold CTRL and click the next two symptoms: "entire crown is ..." and "distress cone ..." - still no "lead contender" - look at the list of symptoms, note they are rather generic in nature - thus it makes sense that all the selected culprits are equally suspect at this point

6. hold CTRL and click "snags and broken stems common" - note the change - Tomentosus & Armillaria are considered "more likely" than the others - but still there is no definitive sign/symptom selected ... also, a tree can have more than one disease/pest problem

7. hold CTRL and click "white fan-shaped ..." - note the change - Armillaria is now clearly the "lead contender" (but we still keep in the back of our mind the possibility that there may be more than one culprit)

This exercise is a good one for developing critical thinking from a diagnostic perspective.  If you can, step back and consider that this very same line of thinking is used to diagnose human health problems and even car problems.  This is an exercise in trouble shooting the cause of a problem.  It is a skill that may serve you well in other endeavours.

Try again with a different selection of S&S.  You can learn quite a bit about the 'thought process' of diagnosis just by playing.  Have fun.

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