Beech bark disease: patterns of spread and development of the initiating agent Cryptococcusfagisuga

Abstract

Beech bark disease occurs when beech trees, predisposed by infestation of the beech scale Cryptococcusfagisuga (Lindinger) (C. fagi (Baer.)), are infected by species of the fungal genus Nectria. Infestation patterns of C. fagisuga on individual trees and in forest stands were studied. Fagussylvatica L. was infested artificially with C. fagisuga. After 3 years, secondary colonization on individual trees was generally restricted to within 1 m from points of introduction. Cryptococcusfagisuga was associated positively with the bark lichen Lecanoraconizaeoides Nye ex Cromb. and negatively with the bark fungus Ascodichaenarugosa Butin. In a young plantation, patterns of scale infestation were related to distance from a large old relic tree and to wind-direction records for the insect's dispersal period. In another plantation the infestation patterns were associated with site topography. In North America, the pattern of continuous spread of C. fagisuga (and of associated disease development) since its introduction in 1890 strongly supports the sequential nature of the causal agent complex proposed by Ehrlich and suggests that susceptibility of F. grandifolia Ehrh. to infestation is so high, at least in the first encounter, that environmental factors which might influence this susceptibility are unimportant in the disease complex.