1720 



ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 



Fig. 1. Tuber Affected With Scab. 



the diseased area. These spots are rarely 

 more than one-half of an inch in diame- 

 ter, although many such spots may grow 

 together, forming large scabby areas over 

 the surface. 



Cause 



The fungus causing this disease is a 

 very minute form. Spores are formed 

 that are but little larger than some of 

 the bacteria. It is a parasite, but is able 

 to live in the soil, in old stems or decay- 

 ing vegetation for several years. Tur- 

 nips, beets and mangels are sometimes 

 affected. 



Control 



Avoid planting on alkaline or heavily 

 manured soils. Where the soil already 

 contains the fungus, practice rotation 

 with crops not affected and where pos- 

 sible plow under green crops. 



Avoid planting scabby seed on land 

 that is clean. If it is necessary to use 

 potatoes that are scabby, the following 

 seed treatment should be given: 



1. Use a solution of one pint or pound 



of formalin in 30 gallons of water, soak 

 the potatoes in this for two hours, then 

 spread them out to dry before cutting. 

 The sacks or crates should also be treated 

 at the same time. 



2. When a large quantity of seed is to 

 be treated the gas method will be more 

 simple. This method consists in pro- 

 ducing formalin gas by adding commer- 

 cial formalin to potassium permanganate 

 crystals. An air-tight shed should be 

 provided large enough to hold whatever 

 quantity it is desired to treat and pro- 

 viding for an open space near the center, 

 which should be about six feet across. 

 The potatoes to be treated should be dry. 

 They may be kept in sacks or crates and 

 should be stacked in such a way that air 

 spaces are kept open around them. For 

 the gas generator use a large pan or tub, 

 place this in the center of the open space 

 and spread the crystals of permanganate 

 over the bottom. When all is ready add 

 the formalin and leave quickly to avoid 

 the suffocating fumes. Use these sub- 

 stances in the proportion of 23 ounces 

 potassium permanganate with three pints 

 of formaldehyde to every 1,000 cubic 

 feet. Keep the shed closed as tightly as 

 possible for 24 hours. At the end of 

 this time it may be opened and the po- 

 tatoes taken out. 



Since the gas is more effective in a 

 humid atmosphere, it is a good plan to 

 sprinkle the floor with water before start- 

 ing the sterilization. 



Potato Wart, Potato Canker 



Synchitrium endoMoticum Perc. 



This is one of the most important Eu- 

 ropean diseases. It is caused by a fungus, 

 and is extremely difficult to control. It 

 has been introduced into Newfoundland. 

 On the severely affected tubers it causes 

 coral-like scaly nodules, which are read- 

 ily recognized. Seed potatoes may be 

 slightly affected and escape notice. The 

 danger of the introduction of this disease 

 has been greatly reduced by the quaran- 

 tine which the United States Department 

 of Agriculture has placed on all foreign 

 countries in which it is known to exist. 



