Bulletin 214, Cotton Diseases in Florida


tion tests on large numbers of gin-run seed, a high percentage of
those that failed to germinate were found to contain Diplodia in
a viable condition.
 SYMPTOMS
 The early stages of infection by Diplodia offer no distinguish-
ing characteristics. In Gainesville, where most of the work on this
disease has been done, a large percentage of the primary infec-
tion of the bolls seems to be caused by bacterial blight, and it has
been impossible to bring in blight lesions on the bolls early enough
to avoid infection by Diplodia. As a consequence of this it has
been hard to distinguish between the two until the rot was rather
far advanced. However, the diseased areas seem to enlarge much
faster in the case of secondary infection by Diplodia, since almost
half of a boll will appear to be water-soaked and darkened after
24 hours during moist weather. After another 24 hours the entire















 Fig. 8.-Cotton bolls showing injuries caused by Diplodia.
boll will be darkened, rather soft and somewhat shrunken, with
small tufts of dirty white mycelium occasionally appearing. After
this the boll becomes hard and the fruiting pustules of the fungus
appear. Vast numbers of spores are extruded by these pustules,
the pycnidia. In wet weather the spores at first are white in color
but become black after a short while. When the boll is thoroughly
dry the masses of black spores give a sooty appearance to the boll
that is very characteristic. The lint of such bolls is badly rotted,
very dark in color, and utterly worthless. Bolls infected with
Diplodia usually do not open, and if they do only expose lint that
is badly stained and of very inferior quality. Bolls that have
been rotted by Diplodia are shown in Fig. 8.