Control. Use resistant plants where possible. The University of California has a list of moderately resistant ornamental shrubs. Treat soil
where plants have died of the disease with carbon bisulfide, and wait
60 days before replanting.
A similar mushroom root rot (Clitocybe tabescens) is important in the
decline of citrus trees in Florida. It also is responsible for ill-health of
about 200 ornamentals, with Australian pine very susceptible.
TEXAS ROOT ROT (Phymatotrichum omnivorum)
is the most destructive
plant enemy in parts of the Southwest, attacking and often killing
more than 1700 kinds of plants, with an annual loss of a hundred million
dollars in Texas alone and about half that in adjacent states. The rot
occurs from July to frost, killing plants in circular spots ranging from
a few yards to an acre in diameter. The ground is covered with yellow
to buff mats of mycelium and white cottony spore mats. Dark-brown
or black rhizomorphs carry the fungus through the soil to other roots.
Control. Replace diseased plants with resistant varieties, which include most of the cotyledons. Ammonium sulfate will sometimes save
a valuable ornamental tree. Make a ridge of soil around the tree at the
end of the branch spread; work 1 pound ammonium sulfate into the
soil for each 10 square feet of surface and fill the basin with water; repeat
in 5 to 10 days.
SOFT ROT (Erwinia carotovora).
This is a vile-smelling, gooey disease of
iris, often following borer injury, and of yellow calla lilies. It is
also a vegetable rot, more common on stored root crops than those in
the field. The bacteria enter through wounds, and in warm, wet weather
the rot is very rapid, rhizomes or fleshy roots becoming soft and pulpy
with a most offensive odor. In iris the interior of a rhizome may disintegrate into a soft yellow mess while the epidermis remains firm. Tips
of leaves are withered, basal portions shredded.
Control. Keep iris in full sun, uncrowded, and with upper part of
rhizomes exposed to the sun. When it is the year to divide iris, do it as
soon as possible after flowering, cutting away all portions with any trace
of rot and disinfecting rhizomes and leaf fans, after they have been cut
back to 6 inches, in a pail of bichloride of mercury (2 tablets to a quart of
water) for 20 to 30 minutes. Let the plants dry in the sun a day or two
STEM ROT (Sclerotinia sclerotiorum).
This is another sclerotial disease,
but here the sclerotia are large, about the size of peas, black, and
formed loosely in the pith of peony or other stems, or in sunflower heads,
or in a cottony weft of mycelium on vegetables affected with a watery rot.