20 maine agricultural lxplrimlnt station. i914. 



The Source of Spring Infection by Apple Scab.* 



in this country it has been quite generally conceded that the 

 early spring infection by apple scab comes entirely from the 

 spores of the perfect stage of the causal fungus which have 

 been produced on diseased leaves lying on the ground during 

 the preceding winter. In fact all the previously accumulated 

 evidence in America is in support of this position. In Europe 

 certain writers have agreed with this while others maintained 

 that scab infested twigs or young branches were also an impor- 

 tant factor. It is generally agreed, however, that the scab fun- 

 gus is at times parasitic upon young branches and water shoots 

 and in this relation, particularly in the case of susceptible vari- 

 eties, may be the source of considerable injury. 



Conditions during the growing season in Maine in 1912 

 apparently were very favorable to the development of apple 

 scab on the limbs. Early in the following winter specimens of 

 young apple branches attacked by scab began to come to^ this 

 Station from correspondents in various parts of the State. 

 Since limb infection appeared to be so general it seemed that 

 an excellent opportunity existed to determine whether or not 

 the scab fungus would remain alive on these limbs over winter 

 and become a source of infection the following spring. Ac- 

 cordingly Mr. W. H. Darrow, a graduate student working in 

 the writer's laboratory, was assigned to this problem. Ac- 

 knowledgment is made to him for much time spent examining 

 local orchards, making spore germination tests, inoculation 

 experiments and in collecting data on the relative susceptibility 

 of varieties. Also thanks are due to State Horticulturist, 

 A. K. Gardner, and Assistant State florticulturist, H. P. 

 Sweetser, of Augusta, as well as to Mr. George A. Yeaton 

 and Mr. Arthur L. Deering, Oounty Directors of farm demon- 

 stration work for the University of Maine College of Agricul- 

 ture in Oxford and Kennebec Counties for furnishing us with 

 material for study from various parts of the State. 



* Morse W. J., and Darrow, W. H. Is Apple Scab on Young Shoots 

 a Source of Spring Infection? Phytopathology 3: 265. Oct. 1913. The 

 present discussion is a brief presentation of facts given in the previous 

 article. 



