Nina yours are posts I seldom delete unless a triangle
of time and circumstances prohibit reading. Rave on oh
priestess of pathology.

Kits
--- Nina wrote:

Billy M. Rhodes wrote:
Root rot is caused by a bacteria .

I'm sure people on this list know how to ignor
off-topic posts and how
to delete spam, and I'm sure you know, if you see a
post by me, that
you can safely ignor it if you don't want to hear
the ravings of a
plant pathologist.

Almost no root rots are caused by bacteria. After
root rot has set in,
bacteria will follow, but they're almost never the
causal agent. The
causal agent is usually a fungus or a water mold.
Even these may be
coming in after wounding of the roots caused by
insects or nematodes
(or pruning). Often we refer to "root rot
syndromes" to indicate that
the etiology is complicated.

Often in plant pathology we refer to the "Disease
Triangle" whose sides
are "pathogen", "susceptible plant" and
"disease-conducive
environment". Obviously, you can have a plant but
no disease if the
pathogen is absent. However, you can have the
pathogen present but no
disease if the environment is nonconducive. You can
have the pathogen
and a conducive environment, but no disease if the
cultivar is
resistant. All three sides of the triangle must be
present.

Sides of the triangle:
The pathogen: The problem with root rot is that the
organisms are
almost always nearby, if not actually present.
Bonsai growers use
nonsoil mixes rather than soil to reduce the
possibility that root rot
organisms will be present, but if a potting mix is
stored on the
ground, organisms can invade. Commercial peat can
contain water molds
(I've isolated pythium from new bags of peat).

Conducive environment: Another problem is that some
root rot organisms
are encouraged by warm weather (Fusarium,
Phytophthora) and others by
cool weather (Pythium). In bonsai, the most common
cause of root rot
is overwatering. The organism is almost invariably
already in the soil
of a bonsai kept outdoors or which has spent some
time in a greenhouse
(a colleague who is a world authority on
Phytophthora in nursery
environments says you can isolate Phytophthora from
the pots of 20-30 %
of symptomless plants in a nursery. My work with
Pythium in
greenhouses has shown similar results). So when the
environment
becomes conducive (soggy), the stage is set for
disease. Well-draining
soil and the "chopstick" technique of watering are
the best defenses.

Susceptible host: Most species used in bonsai are
susceptible to root
rot. However, we can make a few generalizations.
Mature plants are
less susceptible than seedlings. Overfertilized
plants are more
susceptible than normally-fertilized plants. Plants
that have been
recently pruned or repotted are more susceptible
than ones that
haven't.

This spring when you repot, make sure to look for
signs of root rot: a
foul smell, slimy, soft discolored roots. Remove
all such roots.
Repot in well-draining mix and keep the plant free
from all stresses.
A healthy plant is a resistant plant.

Nina.


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=====
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"Expectations are resentments under construction."

Anne Lamott

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