574 Journal of Agricultural Research vol. vi, xo. i S 



in the spring of 191 5, experiments were set up to determine whether a 

 clean product could be obtained by planting disease-free seed on new 

 land. While these experiments are to be continued another year, the 

 results of the first year's trials were so conclusive and of such importance 

 to the potato-growing industry that it appears desirable to record them 

 at the present time. 



In the spring of 191 5 arrangements were made with several farmers 

 to plant clean seed on lands which had never before been planted to 

 potatoes. The plots planted ranged from one-twentieth of an acre to 

 1 acre in size. Six of the plots were planted on virgin soil reclaimed 

 from the desert for the express purpose of planting with disease-free 

 seed potatoes. Fourteen of the plots were planted on land which had 

 for several years been in alfalfa or grain. On the grounds of the experi- 

 ment station at Jerome, Idaho, other plots were planted with disease- 

 free seed. 



The land at the experiment station was reclaimed from the desert in 

 1910, planted to barley, and thereafter to alfalfa. 



The varieties planted in the test plots were as follows: Idaho Rural, 

 Netted Gem, Rural New Yorker, Pearl, Peoples, Red Peachblow, Bur- 

 bank, Carmen No. 3, and Early Six Weeks. The disease-free seed was 

 selected in the same manner for each plot as follows: Each tuber was 

 first carefully examined for all external evidence of disease, such as 

 common scab and the sclerotia of Rhizoctonia sp. All tubers showing 

 evidence of either of these diseases were rejected. No tubers showing 

 any large amount of infection with powdery dryrot were used. If there 

 was only a small pocket of dryrot present, the infected portion was cut 

 out until the tissues appeared white and clean. The externally clean 

 tubers were then cut, the first cut being made across the stem end. The 

 stem end portion was invariably discarded. If there was no evidence 

 of vascular or other discoloration, the balance of the tuber was consid- 

 ered free from disease and was cut into pieces averaging about 2 ounces 

 each. After cutting, the tubers were disinfected for \]/ 2 hours in a 

 solution of mercury bichlorid (1 : 1,000). 



Throughout the season each plot was carefully watched, cultures being 

 made from time to time as evidence of disease appeared in the plants. 

 Wilt was found in every plot and Fusarium oxysporum was obtained in 

 artificial cultures from stems showing vascular discoloration. Stem 

 lesions and footrots were especially severe in all of the desert (or virgin) 

 land plots. In all of the desert-land plots the plants presented a sickly 

 appearance as compared with the plants in the alfalfa and grain land 

 plots. There were indications in each of the desert-land plots of light 

 yields and of a diseased product. 



At harvest time the following methods were employed to determine 

 the diseased condition of the tubers: In each of the smaller plots 100 

 hills were dug and the product of each hill examined separately. The 



