Florida Agricultural Experiment Station


new areas. If cotton is repeatedly grown, small infested areas
in a field will increase in size from year to year until the entire
field is infested. The disease is also reported as being carried
in the seed, but this is probably only an occasional occurrence.
 The fungus enters the plant through the roots and makes its
 way to the water-carrying vessels of the cotton plant where it
 develops. Infection develops most readily at rather high temper-
 atures, 85F. or above, closely agreeing with the optimum tem-
 perature for the growth of cotton. The presence of the fungus in
 the water-carrying vessels of the plant causes injury in two ways;
 the excretion or secretion of a substance toxic to the plant, and
 by the actual obstruction of the vessels, the former probably being
 the more important. As a result of these injuries the plant mani-
 fests certain characteristic evidences or symptoms of infection.

 SYMPTOMS

 The name "wilt" accurately describes one of the principal symp-
toms of this disease, and the disease may be suspected where
wilting of plants occurs. Shortly after a cotton plant is attacked
by the disease, the leaves show a tendency to become flaccid and
dull green in color. At first the plant wilts in the middle of the
day and recovers somewhat over night. In a day or so, however,
the wilted condition becomes permanent; the leaves dry out and
become brown and shriveled, the browning first becoming evident
in the areas between the main veins of the leaves, and soon fall
off. During moist weather the period of alternate wilting and
recovery may be somewhat prolonged, but once a plant is attacked
by the disease its productiveness is either greatly impaired or is
entirely destroyed. New growth may occur, but it is limited to
the tips of the stem or branches and the older leaves are shed;
this, with the fact that the new growth is dwarfed and weak,
gives a tufted appearance to the plant that is characteristic. Such
a plant develops few bolls and most of these are shed. In some
cases there is a rather vigorous development of lateral branches
that is also characteristic of the wilt disease. This type of growth
is illustrated in Fig. 3. The principal diagnostic character of wilt,
however, is the brown or black appearance of the water-carrying
vessels of the plant, which may be observed by making a diagonal
section through the stalk. The manner of cutting and the appear-
ance of the cut stems of wilted and healthy plants are shown in