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EXPERIMENT STATION. 



[Jan. 



Diagnosis and Advice regarding Insect Injury given m Response to Letters 

 and Telephone Calls, for the Year ending Nov. 30, 10,21 — Concluded. 



The Crop Disease Situation in 1921. 



Department of Botant, 

 Prof. A. V. Osmun, Head. 



About the usual number of plant diseases was reported during 

 the year. Six hundred and thirty-nine diagnoses, representing 

 166 different diseases, were made by the department in response 

 to requests for assistance. However, the season was rather 

 free from serious outbreaks of disease, only three assuming 

 the importance of epidemics. 



Weather conditions are a very large controlling factor in the 

 occurrence and prevalence of plant diseases. In general, 

 periods of heavy precipitation and high humidity during the 

 growing season favor outbreaks of disease. This, however, 

 by no means applies to all plant diseases. 



The season of 1921 opened with an unusually warm and wet 

 spring which advanced vegetation fully a week beyond normal. 

 The longest period of rainfall of the entire year, extending 

 over seven days, from April 27 to May 3, provided conditions 

 ideal for the discharge and germination of the ascospores of 

 the apple scab fungus, Venturia inaequalis, with consequent 

 abundant scab infection of the apple. The most serious out- 

 break of apple scab in years resulted, and certain varieties. 



