THE SWEET POTATO IN HAWAII. 13 
mended. If the soil around the base of the plant is stirred with a 
small stick, the worms will leave their hiding places and can then he 
easily destroyed. 
INSECTS INJURING THE ROOTS. 
Sweet-Potato Weevils (Cryptorhynchus batatse and Cylcs formicarius) . 
Sweet-potato weevils are quite destructive at times, thoroughly 
channeling the roots with larval burrows and causing the vines to 
shrivel and decay. 
As a control measure, all infested potatoes and trash above ground 
should be burned and clean cultivation should be practiced. 
INSECTS INJURING BOTH STEM AND ROOT. 
Stem Borer {Omphisa anastomosalis). 
The stem borer is perhaps the most destructive of all the insects 
attacking the sweet potato in Hawaii. It not only burrows large and 
distinct tunnels in the stems of the plant, but also damages the root 
crop. (PI. IV, fig. 2.) In a severely infested field the vines die and 
the yield of roots is greatly reduced. 
Stomach poisons are of little avail in connection with the stem 
borer, as most of its life is passed within the stem or the roots. Prob- 
ably the most effective way of combating it is by the practice of clean 
cultivation. All infected vines and roots should be gathered and 
burned. In severely infested small areas the borers can be crushed 
within the stem by the pressure of the ringers up and down the 
tunneled vines. 
FUNGUS DISEASES AND MEANS OF CONTROLLING THEM. 
The sweet-potato plant is attacked by a number of diseases which 
are divided into two classes: (1) Those attacking the crop in the 
field, and (2) those attacking the crop in storage. 
DISEASES ATTACKING THE CROP IN THE FIELD. 
Black Rot {Sphaeronema fimbriatum). 
Black rot, due to the fungus S. fimbriatum, is not confined to the 
field, but also attacks the crop in storage. Infected roots, when 
taken from the field, show discoloration in small patches which enlarge 
and finally affect the whole root. Cooked sweet potatoes which are 
affected with black rot have a bitter taste. 
Stem Rot (Fusarium batatatis). 
Stem rot, caused by an organism (F. batatatis), commonly attacks 
the plant and its roots. As the name indicates, the stem is affected, 
usually becoming blackened in the advanced stage, and the foliage 
turns a dull yellow and drops. As a rule the vine wilts, and in the 
instances where it does survive the roots are discolored. 
Scurf (Monilochsetes infuscans). 
Scurf, also known as soil stain, is due to a fungus (i¥. infuscans) 
which adheres in such a way to the roots as to be mistaken for soil 
particles. It is not a serious disease and damages the potato only by 
