POTATO LEAP-ROLL. 9 



therefore strongly to be recommended that no seed be planted 

 except that known to come from healthy fields. If there are none 

 in the neighborhood, seed should be brought in from outside. Leaf- 

 roll is not known to occur in Minnesota, Wisconsin, or Michigan. 



The expense of. bringing seed from distant points and the uncer- 

 tainty of getting a vigorous stock of the variety desired emphasize 

 the great need of a better organization of the potato growers for 

 seed selection and inspection. It should be possible to buy seed 

 potatoes accompanied by a certificate from a reliable authority 

 that they are free from disease and of the variety claimed. Such 

 certification should be based on a field inspection made in early 

 autumn, when the foliage is still alive. Leaf-roll can not be detected 

 by an inspection of the tubers. 



In purchasing seed potatoes, those infected with Fusarium wilt 

 should also be avoided. Any lot where many tubers show a brown f 

 discolored ring when cut across the stem end should be discarded. 



Crop rotation is absolutely essential to permanent potato culture. 

 It is a common practice to grow several successive crops in new 

 western land, but this always has one inevitable result — diseases are 

 introduced and spread until it is no longer possible to grow potatoes 

 with profit. Must every community and every farmer learn this 

 lesson separately, or will the experience of the many profit the remain- 

 ing few ? 



There is abundant land in every irrigated district for a long rota- 

 tion, and particularly at this time when so few potatoes are being 

 planted it is possible to put them on land that has not been in this 

 crop for four or five years. 



Cultural methods may reduce the injury from leaf -roll and other 

 diseases. No pains should be spared to give the potato crop the 

 care and attention needed for its most favorable development. Some 

 of the most essential points are given by Prof. L. C. Corbett in Circu- 

 lar No. 90 of the Bureau of Plant Industry, as follows: 



PREPARATION OP LAND. 



Since the potato is a deep-rooted crop and forms its tubers beneath the soil, it standa 

 to reason that it requires a much deeper seed bed than will be necessary for cereal 

 crops. In fact, the preparation for potatoes should be as deep and as thorough as for 

 sugar beets, whether in the irrigated or in the humid region. If a preparatory crop, 

 such as alfalfa or clover, is to be turned under for potatoes, it is advisable to plow this 

 crop under in the fall and to compact the soil sufficiently to make it a good retainer for 

 water, but not so smooth that it will blow. Before planting in the spring the land 

 should be made fine to a depth sufficient to admit of planting and cultivation. If 

 unusually dry the land should be irrigated before the crop is planted. If the normal 

 precipitation has occurred during the winter and spring months, the crop may be 

 planted without irrigation. It is not advisable, however, to plant the crop in dry, 

 hot earth and to immediately irrigate it. Irrigation should precede rather than follow 

 [Cir. 109] 



