Florida Agricultural Experiment Station


appearing in new fields around water holes and other places
where cattle have congregated after having had the range of
neighboring infested fields.
 Wilt may attack watermelon plants in any stage of their
 development. Seedlings may be killed before they appear above
 ground. Also, after appearing above ground, they are often
 killed by a damping-off form of the disease, as illustrated in
 Fig. 3. Growers generally are not familiar with these forms
 of the disease, as losses of individual plants usually are not
 noticed because of the large number of plants in a hill. How-
 ever, after the plants
 have been thinned to
 a stand and have
 Grown larger, af-
 .: fected plants are
-r : more conspicuous
 S., and exhibit distinct
 Sw..ilt symptoms (Fig.
 4). In commercial
 Fields where the in-
 festation usually is
 .. ~ light, destruction
 S" does not occur to
 .. ..*r ..* ,.A any great extent
 .rfs! *.: often until the vines
 i*f .* '' .. are well-grown, and
 *.: .. at this stage the ef-
 fects of the disease
 Fig. 4.-Watermelon plants in the field,
 showing typical wilt symptoms. are very conspicuous
 and disheartening.
Wilted plants may revive somewhat overnight, but the recovery
is only temporary and within a few days the plant is dead.
 Vegetative growth of the fungus extends through the vascu-
lar system of affected plants and serves to impede the normal
passage of water to the leaves by actual plugging of the vessels
and by weakening the water-carrying system by direct attacks
on the walls by the fungus itself or possibly its toxic waste
products. This destruction of the vascular tissue is apparent
as brown streaks in longitudinal sections of diseased stems
(Fig. 5) and as brown or black centers of roots. This char-
acter of the disease has led to its being designated as "black-
root" by growers.