Re: CULT: root diseases - rhizoctonia?

There is another source of decline that became a serious concern among apple
growers in Washington, Idaho and probably elsewhere.  Rhizoctonia is not the
only genus of fungi attacking roots.

 *Phytophthora* (Root Rot) is a genus with some 60 or so species that has
invaded ecosystems where it has not previously been present.  *Phytophthora
cinnamomi* has attacked oaks and can be responsible for abrupt death after the
effects of the infection of the roots has become advanced.  Another species
mentioned is *infestans.*

I don't ever recall hearing a species name mentioned in the apple industry,
just the genus.  The problem has been severe with certain clonal rootstocks
used for dwarfing the size of apple trees.  Nearly all plantings, both in the
eastern US as well in the west, and as far as I know in Europe as well are now
planted on clonal stock to bring the size of what naturally is a rather large
tree to small, more easily worked dwarf trees.  Some of those plantings have
had to be replaced prematurely because the root variety proved to be
susceptible to the kind of decline Linda Mann mentions in her remarks about
*Rhizoctonia* infections.  In those cases, however, it was *Phytophthora* that
was responsible.

There is no reason to assume garden irises are immune to these kinds of
pathogens, and they may well be responsible for the failure to thrive of some
varieties in some areas.

The search for the causes of scorch have included looking for these pathogens.
I don't believe the disorder has been found to be associated with any of these
or similar organisms.  That does not mean *other* kinds of disorders might not
be.

Neil Mogensen   z 7   western NC

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