Apr. 8, 1918 



Relation of Soil Fungi to Potato Diseases 



75 



chance of contamination between the disinfecting bath and the field 

 could be entirely removed. 



During the growing season, inspections of each plot were made from 

 time to time; but frequent frosts prevented an accurate determination 

 of foliage and other diseases of the plants. Disease determinations were 

 therefore reserved until harvest time. Those presented in this paper 

 are confined to such diseases as were observed on the tubers when dug. 

 At harvest time disease conditions were determined by digging 100 or 

 more hills in different parts of each plot and examining the tubers from 

 each hill separately. Disease percentages are expressed in terms of the 

 percentage of hills infected with each disease and in the percentage of 

 tubers infected. Vascular infection due principally to Fusarium spp. 

 was the most abundant. Tuber-rots were occasionally found. Common 

 scab and the sclerotia of Rhizocionia solani were found on a small per- 

 centage of the tubers in most plots. The disease conditions observed 

 in the several plots are given in Table I. 



Table i. — Description of potato plots and percentages of disease observed at harvest 



Previous cropping. 



Character 

 of farming. 



Variety of 

 potatoes. 



Percent- 

 age of 



diseased 



tubers 



(by 



weight). 



1910-11, grain; 1912- 



1914, alfalfa: 



1915, wheat. 

 1908-9, grain: 1910- 



II, fallow: 1912- 

 1915, grain. 



{1910-11. grain; 1912- 

 191S, alfalfa. 

 {1907, oats; 1908- 

 1915, alfalfa. 



{1908, wheat; 1909- 

 1915, alfalfa. 



'1911-12, grain; 1913- 

 i 1915, clover. 

 '1910, barley; 1911- 

 , 1915, alfalfa. 



Irrigation 



do. 



People's . 



.do. 



do 



.do 



See plot 7. 



Virgin desert land . . 



{1913, fallow; 1914, 

 barley; 1915, fallow. 



Virgin desert land . . 



.do. 

 .do. 

 .do. 



, /Netted Gem 



°° \Idaho Rural. 



{Idaho Rural. 

 Netted Gem 

 (Netted Gem. 



■[Carmen 3 



I Six Weeks.. 

 /Irish Cobbler 

 \NettedGem. 



{People's .... 

 Idaho Rural. 

 i Idaho Rural. 

 Netted Gem. 

 People's .... 

 Six Weeks. . 

 f Netted Gem. 

 IPeopIe's .... 

 /Idaho Rural. 

 INettedGem. 

 (Idaho Rural. 

 ■^Netted Gem. 



IPearl 



See plot II. . 



....do 



....do 



.do 



...do 



Dry farm 



do 



26.6 

 16. 2 



10. 1 

 8.2 

 6.0 

 1. 1 



10.7 



12-3 



8.9 



4-3 

 10. 7 

 19.0 



90 

 20.0 



7-0 



22.4 

 II. 4 

 29' 3 

 48.0 

 39- o 

 8.0 

 7.0 

 4.0 

 (a) 



C) 

 (°) 



o No percentages determined. 



In plots 12 to 14 no accurate estimate of the percentage of diseased 

 plants or tubers could be arrived at. No rains fell on the plots after 

 planting time and no previous cultivation to conserve the moisture had 

 been given the land. The plants remained very small throughout the 



