Is it possible? Um, sure, but probably within limits. Probably something you could write a thesis on, if you did it well enough, the point being, IF you were able to do it sufficiently well.
You would need to get data that indicates the disease status of a set of trees, for EVERY possible disease you would need to track.
Then you would need to get a great deal of imaging of diseased and healthy trees, probably in multiple different wavelengths of light, as some things may well not show up, unless you are looking in the correct band of light. Of course, if the leaves have all fallen off the tree and it is dead, then it is likely it had some disease.
Finally, and only when you have sufficient information to be able to track the disease status of a tree, would you even bother thinking about how to do this in MATLAB. Until then, this is not a question about MATLAB at all.
