In the following brief account only the plant diseases and not 
the insects are considered. As will be seen, the total list of potato 
diseases is a formidable one; but, fortunately, we have remedies 
for most of them; while others, like chestnut-blight, still remain 
unsolved. 
We may classify potato diseases according to their causes 
as follows : 
* / 
Caused by \ 
Parasitic Diseases/ 
(Contagious) ) 
Supposedly Non- ( 
Parasitic, butherit- l 
able through seed I 
Non-parasitic 
(Not contagious) 
Fungous — Early blight ; late-blight, or downy mildew; Fusar- 
ium dry-rot; Fusarium wilt; Verticillium wilt; Rhizoctonia, 
or Russet scab; potato wart, silver scurf; leak. 
Bacterial — Common scab; black-leg; soft rots; bacterial wilt. 
Slime-mold — Powdery scab. 
Curly dwarf; mosaic (?); leaf-roll (transmissible through contact). 
Spindling sprout; internal brown spot; net-necrosis; blackheart; tip- 
burn, sun-scald; arsenical poisoning ; formaldehyde 
injury; lightning injury ; frost injury. 
♦Diseases in ordinary type affect mainly the tubers. 
Diseases in italics affect mainly the plant above ground. 
Diseases in heavy face type affect both tubers and foliage. 
The above list may at first glance even tend to frighten one 
away from raising potatoes, especially when we consider 
that the insect troubles are to be added to the above. But, as 
mentioned above, we have remedies for most of these diseases. 
These remedies we may group under seed selection , seed disinfec- 
tion, and spraying. To these should also be added rotation of 
crops. 
The ideal way to raise potatoes is to plant clean seed, obtained 
from healthy plants and hence free from disease, on soil which 
has been properly fertilized and rotated to other crops for a per- 
iod of 3-5 years. It is usually recommended, particularly in more 
southern localities, to plant seed raised farther north. At times 
(and this seems to be particularly true this year) seed potatoes 
come to us badly diseased. If these tubers are carefully selected, or 
sorted over, before planting and all discarded that show disease, 
either externally or internally, or any signs of bruising or decay, 
or discoloration of the flesh, most of the above diseases can be 
largely avoided. In some eases, in order to insure healthy seed, 
it may even be necessary for the potato seed grower to go into 
his fields and there “rogue” the growing crop in order to detect 
and pull out the “rogues”, such as those affected by blackleg, 
leafroll, curly dwarf, or wilt diseases. This field inspection 
should be done at least twice: once during blossoming time, and 
again just before harvest. 
Seed disinfection with formaldehyde (formalin). — This treatment is 
designed mainly for common potato-scab and for black-leg. The 
potatoes should be soaked 2 hours in a solution containing 1 pint 
of formaldehyde to 30 gallons of water. This may be used over 
and over again for at least ten times without losing much strength, 
provided that the barrel containing the solution be kept well 
covered. 
