40 BULLETIN 45, HAWAII EXPERIMENT STATION. 
The disease occurs in the Atlantic States and also in the Pacific Coast 
States. In general the Verticillium can not be considered as serious 
as the Fusarium wilt, since only scattered plants in a field are 
attacked. Once a field is infected, however, the disease becomes 
more serious from year to year if cultivation of susceptible crops is 
continued. 
Control. — The control measures suggested are the same as those 
for the Fusarium wilt (p. 19). In the rotation the following suscep- 
tible plants must be avoided: Eggplant, tomato and other solana- 
ceous plants, okra. brambles, and cotton. 
Leak or Melters (Rhizopus nigi'icans and PytTvium debaryanum) . 
Leak or melters, the name applied to a rapid soft rot of tubers 
occurring in the delta lands of California, is a type of decay often 
causing serious loss in shipments to markets. The disease was at 
first attributed to the common bread mold fungus Rhizofus nigricans, 
but recent investigation has shown that it is in large part due to the 
fungus Pythium debaryanum. These fungi enter through wounds 
in the tubers made in digging. 
Control. — Careful handling in digging and the sorting out of all 
bruised tubers previous to shipping has been found a practical means 
of control. 
NONPARASITIC DISEASES. 
Internal Brown Spot and Net Necrosis. 
Brown spots and streaks in the flesh of the potato and more or less 
widespread net necrosis or netted brown streaks (vascular threads) 
occasionally occur under conditions of growth that are not well 
understood by pathologists. Dry weather and soils possibly deficient 
in some element of plant food are thought to be associated with 
this trouble. As found on the mainland it is sometimes associated 
with temperature changes, probably both during the maturing period 
and in storage. It is significant that neither internal brown spot 
nor net necrosis has been observed here, where a uniform tempera- 
ture is the rule. 
Curly Dwarf, Leaf Roll, and Mosaic. 
The diseases known under the names curly dwarf, leaf roll, and 
mosaic are all imperfectly understood and the causes are entirely 
unknown at the present time. The first two are inherent troubles 
which appear to be associated with weakened strains of potatoes. 
