104 PROTECTION OF PLANTS, 1921-22 



leg, blight, etc. and expect to get potatoes. If it is impossible to obtain first 

 class, clean seed the next best thing is to treat what is available. 



4. For seed tuber treatment two chemicals are available :— mercury 

 bichloride, which is a deadl}- poison, and formaldehyde which is also a poison, 

 but which warns one by the gas given off. 



Mercury bichloride or corrosive sublimate treatment 



Soak the seed tubers in a solution made of 4 ozs. of mercury bichloride 

 in 30 gallons of water for half an hour. If Black scurf is present treatment 

 for a longer period is advisable acording to the work of Howitt at Guelph 

 (see p. 91). The addition of one ounce of mercury bichloride to the 30 gallons 

 of water after each sack has been treated will keep the solution up to strength. 

 If larger quantities are to be treated vats should be used so that the tubers 

 can he handled in crates. It is important to remember that with corrosive 

 sublimate (mercurj' bichloride) no metal vessel can be used. Treated tubers 

 are poisonous to stock and man. The corrosive sublimate can first be dissolved 

 in 2 gallons of hot water and added to 28 gallons of cold, since it is not easily 

 soluble in cold water. 



Formaldehyde treatment 



1. Soak seed tubers for 15 minutes in a solution of formaldehyde made 

 by adding 1 pint (or 1 lb.) of concentrated formaldehyde (commercial of 40%) 

 to 30 gallons of water. 



2. A method recently- tested by Melhus is recommended if the grower 

 can arrange a tank in which formaldehj'de solution of double the above strength 

 is heated to 118° to 122° F. In this case the tubers are soaked for two 

 minutes at this temperature and then covered for an hour before cutting. 



5. If it is not convenient to plant immediately after the completion of 

 seed tuber treatment, care mast be taken that the treated tubers are not placed 

 in sacks or containers which have not been disinfected. 



6. When cutting the tubers discard all rotted stock and also those tubers 

 showing browning or blackening in the vascular ring at the stem end. It may 

 happen that the discarded tuber would give a health}' plant but the chances 

 are against it and "safety first" is a wise saw. 



7. During the growing season give the plants good cultivation. 



8. Spray thoroughlj^ with Bordeaux mixture from the time the plants 

 are eight inches high. IMake the applications about everj' two weeks depending 

 upon the weather. If the weather is moist and warm and plants are deve- 

 loping new leaves very rapidly they must be covered with spray and hence 

 spraying may have to be done every ten days and perhaps later during a drier 



