262 MINNESOTA STATE HORTICULTURAL SOCIETY 



so, thej^ may be spread in the soil by the natural drainage, and land 

 receiving the drainage from infested fields inaj- become infested 

 even without ever having potatoes on them. 



(2). Scabby seed, when planted on new or old potato land will 

 generally produce a scabby crop, but the amount of the disease will 

 generally be much more on the old than on the new land. 



(3). Perfectly clean seed planted on land which is free from the 

 scab fungus will alvvaj-s and in any season produce a crop of smooth, 

 clean potatoes, no matter what the charaeter of the land, but appar- 

 entlj^ clean seed potatoes may have 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 somewhat 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 

 3'et, be treated with mercuric bichloride. 



(4), Land infested by the germs of this disease will always pro- 

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

 the seed used. 



(5). Scabby potatoes should be dug as soon as mature, since the 

 scab fungus continues to work on the potatoes as long as they are 

 in the ground. 



(6). Scabb}^ potatoes may safely be used for seed, provided they 

 are first treated with corrosive sublimate, as recommended. The 

 cost of this treatment is a mere trifle. 



LATE BLIGHT AND ROT OF THE POTATO. 



PROF. S. B. GREEN, ST. ANTHONY PARK. 

 In this state, we are j^et comparativel}^ free from serious loss from 

 this trouble; yet, in the older sections of the state, considerable loss 

 annually occurs to the potato crop from one or both of these 

 troubles, and in occasional years very serious damage results from 

 them. It is, undoubtedly, true that the loss from this cause is verj- 

 generally underestimated or not considered at all. It is the object 

 of this article to discuss this subject brieil}^ and to give the best 

 known methods of combating the disease. 



LATE BLIGHT OF THE POTATO OR ROT. 

 {Phytophthora infestans.) 



Late blight of the potato and potato rot are the result of the grow- 

 ing in the leaves or tubers of the potato of a fungus plant, or mil- 

 dew, which by its growth robs the plant on which it grows and pre- 

 vents the natural use of the food formed in the jilant, and even goes 

 so far as to break down the tissues in which it grows, causing their 

 premature decay and death. 



It has been known for fifty years. It attacks medium or late pota- 

 toes and seldom, if ever, injures earlj-- potatoes. It most generallj' 

 makes its appearance in July or August, causing the leaves to die 

 before the potatoes are more than one-half or two-thirds grown. It 

 is most prpvalant during moist, warni weather, when the fungus 

 may often be seea as a delicate frost— like mildew on the stems or 

 leaves of the potato vines. In seasons favorable to it, the tops of the 



