28 BULLETIN 45, HAWAII EXPERIMENT STATION. 
gested with the assumption that in the absence of the potato for a 
number of years the organism would die out. Inasmuch as turnips, 
beets, and other root crops are susceptible to attack, they should not 
be included in the rotation, as they would serve to carry over the 
disease. 
Potato Tuber Rots (Phytophthora infestans, Fasarium oxpsporum, 
F. radidcolcL, and F. coeruleum). 
In spite of the fact that the major part of the potato crop of the 
islands is consumed soon after the tubers are dug, the total annual 
loss by rotting is an item of considerable importance. It is a serious 
source of trouble in keeping seed stock and often results in the use 
of inferior tubers for this purpose. 
The type of rot most commonly observed is often called dry rot, 
though this name is frequently misleading, as the nature of the rot 
depends upon the amount of moisture and upon the temperature. 
With plenty of moisture and a moderately warm temperature the 
rot develops rapidly and is of the soft type. If the rot develops 
more slowly, or if wet rotting tubers dry out, the typical dry-rot 
phase is produced. These forms of rot are caused for the most 
part by three species of Fusarium known as F. oxysporum, F. radi- 
cicola, and F . coeruleum. Hotting of the tubers is very prevalent in 
the crop from wilt-infected vines. 
Another tuber rot is caused by the late blight fungus. When the 
tops are destroyed by this blight, the tubers may rot badly in the 
ground. The spores of the fungus are washed from the leaves to 
the ground and thence to the tubers, which are infected. This rot 
is a firm brown discoloration extending through the surface layers of 
the tuber a short distance beneath the skin. In the earliest stages 
it shows through the skin as a slight brownish or purplish area, which 
later becomes more or less shrunken. In heavy, cold, wet soils this 
rot spreads rapidly through the tuber, and a soft, ill-smelling, second- 
ary rot caused by bacteria hastens the destruction. In drier soils 
little evidence of rot may be present, and yet the tubers, if infected, 
will rot badly in storage. 
Control. — The rotting of potatoes can be largely controlled by 
storage at a temperature of about 35° F., and where low temperature 
facilities are at hand such storage offers a practical means of con- 
serving the potato crop. However, even at this temperature the rots 
progress slowly, and for best results the tubers should be carefully 
sorted before being put into storage. Storage facilities at such a 
temperature are rarely available to Hawaiian growers, and at pres- 
ent little advantage can be taken of this method of holding the crop 
or seed tubers. To prevent loss through rotting under conditions in 
the islands, attention should be directed toward the prevention of in- 
