270 STATE BOARD OF AGRICULTURE. 



of identity of tho organisms isolated from various types of vascular 

 discoloration. The net outcome of these studies has been to. show that 

 Fusarium wilt is i)resent in a large percent of our field stock and to 

 enable us to diagnose accurately the sj^nptoms found in light attack. 



By infection experiiiienis with potato tubers at ditlerent degrees of 

 huniidity and at a range of temperatures, the fact has been established 

 that Fusarium oxysporum is an important agency in causing tuber 

 rots, but its activity depends upon high temperature and high humidity. 



The toxicity to the potato vine of filtrates from old cultures of 

 Fusarium has been proved conclusively. Synthetic solution in which 

 the potato Fusarium had been grown for some weeks was filtered from 

 mycelium and spores b}^' means of a Berkefeld filter. Cuttings from 

 healthy vines when placed in this tittered solution wilt in less than 24 

 hours, while checks in both distilled water and in sterile synthetic solu- 

 tions remain turgid. These results are of far-reaching importance in 

 contributing to our knowledge of the cause of the wilt produced by this 



fungus. 



The field studies with this disease have already yielded results of 

 practical value. By plot tests, tubers which were freed from infection 

 by cutting off diseased parts were compared with whole tubers and the 

 superiority of the former has been conclusively shown. The infected 

 butt-pieces showed a practical failure when planted. 



For ordinary agricultural practice this warrants the recommendation 

 • to reject a one-inch slice from the butt ends of potatoes in process of 

 cutting for planting. This practice is being given a further test the 

 present season. Mr. Goss is planning to complete the work on Fusarium 

 wilt at the University of Wisconsin next year, in pursuance of studies 

 for a higher degree. 



Celery Work. In the report for last year an outline of the serious 

 soil disease of celery was given. This stunting disease has been studied 

 during the past fiscal year and control measures on a still larger scale 

 than previouvsly tried were undertaken. One-third acre of infected soil 

 was steamed this past spring and demonstration was made that, with 

 equipment in good running order the steaming can be done at a cost of 

 less than $150 per acre. This lowering of price per acre comes from the 

 use of large steam pans. These large steam pans are arranged to be 

 lifted by levers and moved on wheels which run upon planking. Each 

 pan covers nearly 100 sip ft. at one application. 



The celery work has now reached a stage where it can be successfully 

 carried to the growers. AVe believed we are justified in beginning a 

 campaign to lead owners to steam their fields where the infection is 

 showing only in spots. These spots are of course a source of danger to 

 the rest of the fields and it is only a matter of time until the disease 

 completely infects the now slightly infected areas. 



Attention has also been given to the Septoria Leaf Spot disease of cel- 

 ery commonly known as Blight. Study on this disease was carried on 

 by Mr. Ezra Levin during the last summer. The work begun by him was 

 completed in the winter and a special bulletin detailing the practical ap- 

 plications of the work has been prepared and given wide distribution in 

 celery-growing centers. The work on the Septoria disease was especially 

 timely, since the late celery crop of Michigan was a practical failure last 



