POTATO DISEASES IN HAWAII. 37 
has very recently been found in gardens in certain mining towns of 
Pennsylvania, and a survey of the infected region is now in progress. 
Black wart is probably brought into new localities on apparently 
healthy or only slightly diseased potatoes coming from infected 
fields, and it is thought to have been introduced into the United 
States on low-grade European table potatoes before the quarantine 
was established. 
Black wart attacks the tubers chiefly and causes malformation 
and warty excresences, converting the tuber into a worthless mass 
(fig 6). The warts have given rise to such names as warty disease, 
black scab, canker, and cauliflower disease. Once infected, a soil 
can not be used for this crop again for many years, unless resistant 
varieties are found, as now seems possible. In the worst cases from 
25 per cent up to the entire crop is affected. The disease grows 
worse each year potatoes are grown on infected soil, but so far as 
known no other crop is attacked. 
The seriousness of this malady may be judged from the following 
quotations : 
A vigorous effort should be made, if found in the United States, to eradicate 
the trouble. All infected tubers should be boiled or burned, and no more 
potatoes should be planted on that field for eight years. Stock should not be 
allowed to run over infected areas and no part of any lot containing diseased 
potatoes should be used for seed purposes. 1 
It has been stated that no sound potato is saved from a crop that is 
attacked. While the virulence of diseases like late blight or early blight is 
more or less dependent upon climatic conditions, this disease is not influenced 
in any known degree by physical or mechanical conditions. It may, there- 
fore, be considered as the most serious pest attacking potatoes. Fields at har- 
vest in affected areas present the most hopeless appearance; the disease has 
caused the greatest havoc in all localities where it has appeared. 2 
Powdery Scab (Sponyospora suMerranea) . 
Powdery scab has only recently been introduced into the main- 
land of the United States, first being found in Maine and subse- 
quently in other New England States and more recently in Oregon 
and Washington, and it is also known to exist in British Columbia. 
This disease, which may be mistaken for corky or common scab, is 
caused by the slime mold Spongospora subterranea. There appears 
to be little indication that it would be serious if introduced here, 
the pathologists of the Eastern States being of the opinion that its 
spread will be largely controlled by climatic and soil factors. The 
fungus attacks the young tubers and develops as they mature in 
the ground. The center of infection becomes a pustular-like scab 
containing the spore balls of the fungus as a brown powder. The 
1 Field, Ethel C. [The wart disease of the potato.] U. S. Dept. Agr., Farmers' Bui. 489 
(1912), p. 23. 
2 Giissow, H. T. A serious potato disease occurring iu Newfoundland. Canada Dept. 
Agr. Bui. 63 (1909), p. 6. 
