Infection periods in Naemacyclus needlecast of Scots pine.

MERRILL, W., B. R. KISTLER, L. ZANG, and K. BOWEN. 1980. Infection periods in Naemacyclus needlecast of Scots pine. Plant Disease 64:759-761. Isolations from 5 yr of complements of Scots pine needles from needle emergence from the fascicle sheath until casting 16-18 mo later showed three infection periods by Naemacyclus minor. Period one extended from the time of full needle elongation (about mid-July) until late August, period two from early November to early December, and period three from mid-April until late August of the following year. During 5 yr of study, periods one and three were periods of major infection, with greatest infection occurring in period three. Increase in level of infection during period two usually was not significant, although fruit body formation was most conspicuous at this time. The incubation period varied from 2 to 16 mo, depending on when the needles were infected. Naemacyclus minor Butin (2) needlecast of Pinus sylvestris (Scots pine) has caused significant quality losses in Pennsylvania Christmas tree plantations for a number of years (5,7,8,11). We have found this disease also in Ohio, West Virginia, and New York, and we believe that the pathogen has been reported previously in California, Colorado, Massachusetts, and Michigan as N. niveus (1,3,4,10). Often confused with feeding damage of the spotted pine aphid Eulachnus agilis or with "premature senescence," symptoms of N. minor infection begin to develop in late September when needles from previous years turn yellow with prominent, transverse brown bars Contribution 1141, Department of Plant Pathology, The Pennsylvania State Agricultural Experiment Station. Approved for publication as Journal Series