THE NEEDLE CAST DISEASE 

 IN CENTRAL NEW YORK 



The development of Rhabdocline pseudotsugae has been traced 

 1>\ several authors (29. 46, 66, 70). In general, the various descrip- 

 tions of tlie development are in close agreement. However, certain 

 critical periods in the life history ot the causal fungus are variable 

 and cannot be predicted without knowledge of local environmental 

 conditions. For example, the time of ascospore maturation and 

 release in a given area cannot be predicted and the duration of spore 

 cast ma\ differ greatly from one area to another. Control measures, 

 to be effective, must be correlated with the proper stage of develop- 

 ment of the fungus. The purpose of this phase of the present study 

 was to obtain detailed knowledge of the development of R. pseudot- 

 sugae in respect to seasonal and environmental conditions existing 

 in central New York. 



DEVELOPMENT OF SYMPTOMS 



After initial infection of Douglas-fir needles by Rhabdocline 

 pseudotsugae in late May or early June, no visible external symp- 

 toms of the disease are seen for several months. The early stages are 

 extremely difficult to detect. The first visible evidences are the 

 minute yellow spots on either surface of the needle. These may 

 appear from September to mid-December in New York, depending 

 apparently on weather conditions. Weir (66) first reported such 

 variations in the development in his original descriptions of the 

 disease. In Montana and Idaho the spots were normally observable 

 in December, but during cool, wet summers and autumns such 

 symptoms often appeared two months earlier. Wilson and Wilson 

 (70) reported that yellow spotting of needles occurred in Scotland 

 as early as June. This early date is puzzling since the authors gave 

 late May or early June as the infection period. The early stages of 

 other disorders, such as aphid injury, nutrient deficiency or winter 

 injury, may also cause yellow spotting of needles. Therefore, such 

 symptoms ma\ be mistaken for R. pseudotsugae, especially if the 

 disease is known to be present in the area. 



Most of the early infections by R. pseudotsugae occur near the 

 tips of the needles. The yellow spots enlarge as autumn advances, but 



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