240 Diseases of Econoinic Plants 



Arsenical Injury, due to insecticides, may be avoided by 

 applying the arsenicals with Hme or with Bordeaux mixture. 



Potato seed disinfection. — The diseases against which 

 seed disinfection is effective are only those in which the 

 fungus is superficial on the tuber, i. e., primarily against 

 common-scab and black-scurf, and against these only under 

 certain conditions. Before disinfecting, all tubers obviously 

 bearing any other disease should be discarded, as well as 

 tubers bearing large black-scurf sclerotia or deep scab pits, 

 since the treatments will not kill the fungi on such. Many 

 diseases of tubers cannot be detected until the potatoes are 

 cut. Before treating, enough of them should ])e examined 

 internally to give satisfaction that the lot is not generally 

 infected with any internal disease, as for example, with 

 black-leg or wilt. Disinfection should he done before cutting. 

 Two chemicals are used according to the following formulae : 



1. Mercuric chlorid (corrosive sublimate). . 4 oz. 

 Water 30 gal. 



2. Formalin 1 pt. 



Water 30 gal. 



Mercuric chlorid must not be brought in contact with 

 metal; is very poisonous to animals; deteriorates rapidly 

 with use, and is more expensive than formalin. The formalin 

 solution may be used in any kind of container; grows stronger 

 on evaporation, and is generally preferable. 



In either solution the potatoes are soaked for a half hour. 

 The solution may be put in a large trough, and the potatoes, 

 in crates or bags, set into it, left the requisite time, then sub- 

 stituted by another lot of potatoes. Potatoes should be 

 dried immediately after treatment. If there is much l^lack- 

 scurf present, and no better seed are obtainable, the potatoes, 

 if dormant, i. e., not sprouted, may l)e soaked for two hours 

 in mercin-ic chlorid solution. With sprouted stock the mer- 

 curic chlorid is more injurious than the formalin, but the 

 formalin is not effective against heavy infection of black-scurf. 



