THE DISEASE 



The first visible evidences of the Rhabdocline needle cast disease 

 appear in the autumn or early winter as minute yellow spots on 

 the upper and lower surfaces of the current year's needles. These 

 spots are irregularly scattered over the surfaces of the needle but 

 occur more abundantly near the apex. During the winter months the 

 spots become larger and darker through an increase in number of 

 necrotic cells in the lesion. By the following spring many of the 

 spots coalesce and become deep red-brown in color, a condition aptly 

 described by Weir (66) as "mottled." In the late spring or early 

 summer the apothecia of the fungus appear as large single fructifi- 

 cations or numerous small ones on each side of the midrib on the 

 lower surface of the needle. The epidermis of the needle splits 

 exposing an orange to orange-brown hymenium consisting of asci 

 and paraphyses. When mature, ascospores are released and inoculate 

 the newly developing needles. The majority of the year-old infected 

 needles fall during the spring and summer and by late summer the 

 only evidence of the disease is the sparse foliage. 



Disease losses are caused by a considerable reduction in growth, 

 serious defoliation of marketable Christmas trees, and killing of 

 trees. Although infected needles may fall during all seasons of the 

 year, the major period of needle casting in New York plantations was 

 in summer, shortly after the maturation of the ascospores. The best 

 time for an accurate estimate of the damage caused by the Rhabdo- 

 cline needle cast in New York plantations is in April. During this 

 month, most of the infected needles are still retained, needle mot- 

 tling is intense and heavily infected needles are completely brown 

 except for the petiole. In May and June, most of the infected year- 

 old needles are already cast. Since infections on new needles are not 

 macroscopically visible during these two months, the only field 

 symptom is the sparse foliage which may be concealed by the new 

 growth in recently infected plantations. 



When diseased trees are cut for the Christmas tree market their 

 needles soon become completely brown, dry rapidly, and are cast. 

 Weistaner (68) cites the disastrous effects of the disease on Montana's 

 Christmas tree industry in the epidemic years of 1947 and 1948 when 

 harvested trees were ready for sale. 



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