SUMMARY AND CONCLUSIONS 



A study of the Douglas-fir needle cast disease caused by Rhabdo- 

 cline pseudotsugae Syd. was carried on from July 1955 through 

 the summer of 1959. Continued attack by this fungus on young 

 Douglas-fir seriously affects the quality and quantity of trees pro- 

 duced for the Christmas tree market. 



The development of the Rhabdocline needle cast disease in New 

 York was studied intensively and found to be intermediate between 

 the development as described for western United States and for 

 Europe. The first evidences of the disease were found from Sep- 

 tember to December depending upon weather conditions. The 

 typical mottling described by previous workers was observed 

 throughout the winter. 



Apothecia were of two distinct types recognizable on the basis 

 of their size and manner of opening and were observed only on the 

 lower surfaces of Douglas-fir needles. Development of apothecia was 

 outlined and average measurements of asci, paraphyses, and asco- 

 spores given. Ascospores germinated readily in the apothecium and 

 produced a dark black lateral germ tube. No imperfect stage of the 

 fungus was found. 



Infected needles were cast throughout the year, but most were 

 shed shortly after dissemination of the ascospores. 



Spore dispersal was of longer duration than previously suggested. 

 Apparently-viable germinating spores were trapped two months 

 after the last Douglas-fir spring buds had burst. From the standpoint 

 of control this means that spray applications must be extended 

 further into the summer than would otherwise be required. How- 

 ever, the time of opening of spring buds and of lammas buds are the 

 critical periods since the tender new needles are apparently very 

 susceptible to infection. High humidity favored dispersal of asco- 

 spores as well as the incidence of infection, but no relationship 

 could be found between spore dispersal and temperature. 



Infection occurred with equal frequency on vigorous as well as 

 on suppressed trees. After a spore settled on a needle surface, the 

 hyaline end deteriorated and spread outward to cement the asco- 

 sporc to the needle. Penetration was through the cuticle of either 



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