EXPERIMENT STATION BULLETINS. 415 



FIELD EXPERIMENTS CONDUCTED IN MICHIGAN IN 1915. 



As the chief work assigned to the author in Michigan was that of ex- 

 periments on the control of the root-knot disease of ginseng, it was neces- 

 sary to make a general survey of the various ginseng gi'owing sections 

 of the state, in order to select a suitable place for establishing a field 

 laboratory. It was finally decided that a large garden located at 

 Muskegon, Michigan, afforded the best opportunity for carrying on field 

 experiments so the field laboratory was located there. 



In order to exclude, as far as possible, any factors which might lead 

 to errors in the results, it was decided that the plots used for experi- 

 ments should be separated from the remaining soil. To accomplish this 

 the plots of soil, seven by ten feet in extent, were enclosed with galvaniz- 

 ed sheet iron thirty-six inches in width. The iron was set into the soil 

 thirty inches, leaving six inches projecting above the surface to keep 

 any surface soil from being washed into the plots after the experiments 

 were started. The observation of nematodes three feet down in the soil 

 has been recorded by Bessey (2) but the difficulty of obtaining iron 

 more than thirty-six inches wide was so great as to preclude our plac- 

 ing it more than thirty inches in the soil. The edges, where the sheets 

 of iron came together, were bent, interlocked and pounded tightly to- 

 gether to prevent the passage of anything at such places. To exclude 

 the possibility of soil being carried onto the plots, by various animals 

 passing through the garden, each plot was enclosed above ground 

 with a three foot fense of chicken-wire netting, which came down so as 

 to overlap the six inches of sheet iron above ground. 



The plots, seven in number, were alternated with two foot paths, so as 

 to cover the greater part of a strip of soil fourteen feet wide and seventy 

 feet long. Two beds of badly nematode infested ginseng roots had been 

 removed from this soil the fall previous, and no crop had been on the 

 ground since. The soil, throughout the whole garden, is a loose, sandy 

 loam, very highly fertilized with barnyard manure, making it an ideal 

 place for the rapid multiplication and spread of the root-knot nematode. 



Although the experiments of previous workers with chemical treat- 

 ments of the soil for the eradication of Heterodei^a raSicicola had given 

 chiefly negative results, it was decided that a series of such treatments 

 should l)e made to test the relative value of various chemicals, with the 

 possibility of finding one that would be both effective and practical of 

 application. 



CARBON BISULPHIDE TREATMENT. 



As previous experiments by Bessey (2) had shown carbon bisul- 

 phide to be successful under field conditions, it was decided that one 

 plot should be treated with this chemical exactly as recommended. On 

 the afternoon of May 10, 1913, plot I was treated with carbon bisulphide 

 as follows: — Holes were made in the soil at intervals of six to twelve 

 inches, and varying in depth from six to eighteen inches. Liquid carbon 

 bisulphide was poured into the holes at the rate of four ounces per 

 square yard of soil, and the holes quickly plugged up by packing soil 

 into them. Within half an hour after the treatment was made the air, 

 in the vicinity of the plot, had a very strong odor of carbon bisulphide, 



