200 



VEGETABLE GARDENING. 



the potato in this section, and the most important of these is the 

 Colorado potato beetle, or "potato-bug," but it may also be in- 

 jured by blister beetles, wire worms and white grubs. (For reme- 

 dies for these pests, see chapter on insects.) 



Diseases. — There are several diseases that sometimes injure 

 the potato. The most common of these are known as the scab 

 and the blight. Scab is a term used to refer to the rough patches 

 with which potatoes are frequently covered. Potatoes so infected 

 are lessened in yield, and on account of being unsightly and 

 rough do not sell readily. The term blight refers to a disease 

 that kills the tops. 



Scab of Potatoes is caused by a fungous plant working in 

 the surface of the potato. The germs of it are very abundant and 

 live for many years in the soil and also over winter on the pota- 

 toes. If these germs are fed to stock they undoubtedly grow in 

 the manure, and the use of such manure may often be the cause 

 of infection. Also they may be spread in the soil by natural 

 drainage and land receiving the drainage from infected fields may 

 become infected with me disease without ever having had pota- 

 toes on them. Scabby seed potatoes when planted on new or old 

 potato land will generany produce a scabby crop, but the amount 

 of the disease will generally be much more on the old land than 

 on the new. 



Perfectly clean seed potatoes planted on land which is free 

 from the scab fungus will always and in any season produce a 

 crop of smooth, clean potatoes, no matter what may be the char- 

 acter of the soil; but apparently clean seed potatoes may hav(^ 

 the germs of the scab fungus on their surface. This is often the 

 case where they have been sorted out from a lot that is some- 

 what infected with scab. In this latter case the tubers should, 

 at least, be thoroughly washed in running water to remove any 

 germs that may be present or, what is better yet, be treated with 

 corrosive sublimate (mercuric bichloride) as recommended be- 

 low. 



Land infected by the germs of potato scab will produce a 

 more or less scabby crop, no matter how clean and smooth the 

 seed used. 



Scabby potatoes should be dug as soon as mature, since the 



