CONTROIv 01? BI,ACKLE;G DISEASE OF THE) POTATO. 211 



acre. The field was examined on July 6 and i8 with the fol- 

 lowing result. 



Seed tubers bruised, untreated. Diseased plants per acre 70 



Seed tubers bruised, treated (formaldehyde solution). 

 Diseased plants per acre 20 



Seed tubers selected, untreated. Diseased plants per acre 10 

 Seed tubers selected, treated (formaldehyde solution). 

 Diseased plants per acre o 



An examination on July 6 of about one-half acre of the 

 immediately adjoining portion of the main field where the seed 

 was so'aked before cutting showed only 2 aflrected plants per 

 acre, while an examination of an equal area on a different por- 

 tion of the same field on July 18 failed to reveal any diseased 

 plants. 



It should be remembered that the season before on this same 

 field and where the seed for this year's planting was pro- 

 duced there were according to Mr. Donaldson's estimate nearly 

 300 diseased plants per acre — a decrease of over 99 per cent. A 

 part of this decrease may, as compared with 1910, be due to 

 unfavorable weather conditions. As has already been pointed 

 out blackleg never does so much damage if the early part of the 

 growing season is dry. 



No blackleg was observed on the volunteer plants which 

 came up between the lows and hills from tubers which re- 

 mained in the soil over winter from the crop of the season 

 before. This taken together with the fact that practically no 

 diseased plants were found over the entire 50 acres where the 

 treated seed was used is additional evidence that the disease 

 did not live over in the soil where it appeared last year but was 

 communicated to the crop of the present year by means of the 

 regular seed tubers. 



The Husscy B~i'periment. 



191 1 was Mr. Hussey's second year of formaldehyde disin- 

 fection for blackleg. In 1909 he observed some of the disease 

 on his field with^ the Irish Cobbler variety. In 1910 from the 

 crop of the season before he carefully selected sound and per- 

 fect tubers sufficient to plant about one-fourth of a 4-acre field. 

 These were then soaked 2 hours in formaldehyde solution one 



