Although its symptoms can
be similar to other diseases, the first signs of
Southern blight would include yellowing of foliage and
wilting of leaves. This disease attacks at or just below
the soil line so there may be black or dark brown
lesions on the lowest part of the stem. In hosta, it may
appear as a brown rot at the base of the leaf petioles.
One of the best
characteristics for identification is the development of
cottony white, threadlike wisps called mycelium that
grow up the stem and may spread out on top of the soil.
The fungus overwinters as
a very small, brown or tan colored structure called the
sclerotia. These can be found on the surface of the soil
near infected plants. It was thought that the reason the
disease was found mostly in the South was that these
structures could not survive the winter cold up North.
However, it appears that they can live as long as they
are covered by a layer of snow or organic mulch.
A related disease, white
mold caused by a relative fungus, Sclerotinia
sclerotiorum, is quite similar. It seems that the
distinguishing feature is that the sclerotia of this
disease are larger (about the size of small rabbit
droppings) and they are usually attached to the lower
stem of infected plants.