Brent Walston wrote:
Pathogenic fungi and bacteria only eat LIVE tissue,

I'll just correct you for the sake of being annoying. There are two
types of pathogenic fungi: necrotrophs and biotrophs. Biotrophs attack
living tissue. Necrotrophs kill tissue, and then eat it. I only bring
up this trivial distinction because fungi are defined as organisms that
excrete enzymes and then absorb their food. Things in the animal
kingdom *ingest* food. So it is easy for a Phytophthora to excrete
nasty enzymes, kill plant tissue, and then grow into it. [note:
Phytophthora is now defined as an alga in the Kingdom Plantae
so the definition for the Kingdome Fungi is now slightly modified].


although some fungi
that start out as composters can, in some extraordinary cases,
convert
to a pathogenic form.

There's a continuum among necrotrophs, from those readily kill tissue
(Pythium, Fusarium, Verticillium)to those that need special conditions.
Something like Choanephora is largely a "composter", but if it gets an
energy boost, it will turn pathogen. Many fungi like this attack
blossoms; they eat the nectar, get strong, then attack the branch.
Botrytis cineria is a weak pathogen, but in the presence of flowers,
wounds, or honeydew secreted by aphids, it will turn mean.

Fungicides can play a role in controlling it, but changing
the environment is the most important part.

No argument!

In most cases, it is the
plant itself that will effect the control by shedding parts of itself
or
walling off the disease. How do tell the difference? This CAN be most

difficult, and often requires an expert. County Ag extension agents
are
trained in this (pathology) and their sub agents or Master Gardeners
may
be able to help. The only real way to find out definitively is to
submit
samples to a plant pathologist, but by then it is usually too late
for a
specific plant.

Too true. Plus, we tend to pull the plant apart to diagnose it. We
suspect root rot if we see wilting on one side of the plant. To be
sure, we look for brown
streaks in the xylem, which can only be seen by carving up the trunk.
Then we culture and if we come up with a root rot pathogen, we tell you
what to spray to save the *currently healthy* remainder of your plants.
We never try to save the plant brought in as a sample!!! Remember
that if you call Cooperative Extension.
For the bonsaist, it makes sense to assume that repotting will solve
the problem. Either you will, or you won't.

Nina.