Don Walker wrote:
Nina,

Are you the Nina Shishkoff, plant pathologist from the LIHRL, that
wrote
"Using Fungicides to Control Bonsai Diseases" at:
http://www.evergreengardenworks.com/fungicid.htm?

Yup. That was me about 10 years ago. I'd have to go back and read it,
but I doubt I advised using any kind of fungicide for root rots,
because it's hopeless. It's *so* much easier to treat foliar diseases.

That article talks about using "An ERADICANT" to "...kill fungi that
have already invaded the plant."

I'll have to look at that article to see if I'm being unclear (it
wouldn't be the first time). The terms "protectant" and eradicant"
refer to the hoped-for action: to either protect the plant before
infection or to act later to eradicate the pathogen after infection.
"Systemic" is a more specific term indicating that the chemical moves
around in living tissue; that's all it means. It's possible to be an
eradicant without being a systemic, but I can't think of an example
offhand, except hydrogen peroxide. But I'm pretty sure in that article
I'm talking about foliar diseases, where many systemic fungicides work
VERY well. If they are fungistatic rather than fungicidal, it doesn't
matter, because if they stop the epidemic during, say, rainy weather,
it doesn't matter if they stop working when the weather is no longer
conducive to disease. With root rots, conditions are almost always
conducive, so a fungistat is a losing proposition.

Would sustained, judicial, treatment of all three types of fungicides
(protectant, systemic, and eradicant) not slow or halt progression of
the infection allowing more time in which to perform repots and
continued isolation and removal of the infected tissue.

Judicial use of all three kinds of fungicides is the backbone of
Integrated Pest Management (IPM)! But as several people already
mentioned, with root rot the best treatment is to improve soil
conditions. If you have a pesticide applicator's license (Jim is
correct: it's the only way to have access to the "good stuff"),and want
to use a good fungistat like Subdue Maxx on a tree with root rot and
*then* trim off the diseased roots and repot into a better soil, that's
a valid plan. But trimming the diseased roots and repotting alone is a
valid plan, too.


I've also read that the use of thiophanate methyl will affect the
mycorrhizal fungi. Should new colonies be introduced after any use
of
this fungicide?

Yes, although you know my feeling about this: mycorrhizal fungi do
nothing in a bonsai pot. They only have an effect in underfertilized
plants, and that doesn't describe *your* bonsai, does it?

I trimmed them back to about half their length - about 18", still
too
long but I was considering the overall quantity of roots tips and
figured I could adjust at the next potting - then treated with
rooting
hormone to increase root mass near the base.

Rooting hormone will inhibit preexisting roots, so it should only be
used when rooting cuttings.

That was several months ago and now I'm getting suspicious that the
tree
may have root rot. I've had a couple of limbs die and while I'm
getting
new growth the old growth seems to be suffering. I'm planning to
repot
to an inorganic soil (lava) of the appropriate particle size and want
to
be prepared for what I find.

I don't know that you have evidence of root rot. You may just have
repot shock. lava soil sounds good, but don't shock the plant any more
than you have to.

Nina, who only uses two pesticides on her bonsai: pyrethrins (for mites
and scales) and bordeaux mix (a protectant for foliar pathogens). Good
growing conditions and regular fertilization are your BEST defense
against disease.