Abstract
Literature embracing many facets of Beech bark disease is reviewed. Scoring systems for assessment of disease symptoms were developed. Surveys indicated that thinned crops contained a higher proportion of trees infested by Beech scale (Cryptococcus fagi), and that older pole-stage crops supported greater populations of the insect. Other disease symptoms were correlated with Beech scale incidence. The most severely diseased crops were of high yield class. Aerial photographs taken before the disease outbreak showed differences in crop appearance in subsequent severely affected areas which were attributable to different forest management practices. Detailed observations on the range of disease symptoms were made. Following infestation of the main trunk by Beech scale, Nectria infection caused extensive bark necroses, producing yellow foliage in the crown. Such trees were moribund. Within an affected forest a mortality rate of nearly 5% a year occurred. Dendrochronological studies did not indicate that damage was initiated in any one year. Ascospores of Nectria from a diseased tree were trapped throughout the year, and their discharge was associated with prevailing wet weather. Nectria isolates infected bark of forest and potted beech only through wounds. Inoculations were most successful during host dormancy. Small cankers were formed but were soon delimited by callus production. Relatively larger cankers appeared to be formed when water supplied to the host was restricted. Increase in girth of pole-stage trees was greatest following a heavy thinning, although over three years Beech scale infestation increased irrespective of thinning treatment. Artificial establishment of Beech scale onto uninfested trees was initially successful. Perithecia were produced by mated cultures of isolates from opposite compatibility types. Characteristics of Nectria associated with Beech bark disease in southern England agreed with those of N. coccinea sensu lato. The fungus grew best between 22 and 27°C. Substantial growth occurred at 5°C.