Does anyone have any suggestions for a systemic fungicide for use on a
Texas Ebony (Pithecellobium flexicaule) with root rot?

I can answer this question with absolute certainty, because I just
finished a study of the effects of systemic fungicides on Phytophthora
ramorum on Rhododendron (come to Austin, Texas this August for the
American Phytopathology Society meeting, and you can watch my
Powerpoint Presentation!)*.

The answer:

Systemic fungicides do NOTHING for an existing infection. They aren't
fungi-CIDES (i.e. fungal-killers), they are fungistatics (fungal growth
inhibitors). The pathogen will stop growing for a couple of weeks,
then it will start up again. The only way to use a systemic is as a
preventative measure, and I don't recommend that for a hobbyist- only
for a professional with thousands of plants.

My reason for looking at this is because nursery retailers in
California are suspicious that big wholesalers are treating plants with
systemic fungicides to arrest "sudden oak death" long enough to sell
them. But my findings are pretty clear: they symptoms are still
visible, even if the pathogen isn't growing, and a PCR molecular test
will detect the pathogen.

Nina, who infected 30 plants last week in order to look at the effect
of systemic fungicides on antibody-based detection methods.

*Any bonsai-related stuff to do in Austin?