Bulletin 208, Cucumber Diseases in Florida


appearance. The fungus penetrates the epidermis only slightly to
obtain its nourishment. As the fungus requires more food, the
leaf begins to turn yellow and a few brown specks can be seen
near the center of the white fungus growth. These spots enlarge
and when very many of them occupy a single leaf it is rapidly
killed.
 Control: In greenhouses it is recommended that the plants be
dusted with flowers of sulphur. In the field the spraying with
Bordeaux mixture or dusting with copper-lime dust for the
control of other diseases is sufficient to control the powdery
mildew.

 SOUTHERN BLIGHT lB


 Southern blight is caused by the
fungus Sclerotium rolfsii Sacc. Al-
though the fungus is very common in
Florida and has been found to be a
serious factor on a large number of
the cultivated and wild plants in the
State, it has not been important on
cucumbers. Its occurrence and de-
structiveness are variable and spo-
radic, depending principally on
weather conditions, being worse dur-
ing the rainy period of the summer
months. A plant once attacked by the
fungus is always killed, as it is usually
girdled at the surface of the soil.
 Numerous sclerotia are developed
which are white when young, gradu-
ally turning light brown and finally
dark brown. They vary somewhat in
size, averaging about the size of mus-
tard seed. (Fig. 28.) These sclerotia
are easily scattered in tilling the soil,
also by rain and running water. They
germinate quickly in a moist atmos-
phere and infect other plants. Once
the fungus is established only a few
days are required to kill the plants.


Fig. 28. Southern blight on
 main steam, showing white
 mycelia and small brown
 sclerotia.