The First Occurrence Of The Beech Scale Insect On American Beech Trees In Ontario

Field and laboratory investigations of alleged recent rapid decline of beech trees on two adjoining woodlots in the Newmarket area in southern Ontario during 1981 and 1982 resulted in the discovery of the beech scale insect affecting American beech. The scale, on the bark of beech, Fagus grandifolia was identified to be Cryptococcus fagisuga (Lind.), (Fig. 1).

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Fig. 1.

The white patches on the bark of mature American beech shows severe infestation by beech scale insect.

The scale insect was introduced from Europe into Nova Scotia about 1890 (2) and is present in Quebec and the Maritime provinces of Canada (1,2) and also in northeastern United States (3,5).

Observations of affected trees in the woodlots revealed that some of the beech had fruiting bodies or cankers resembling Nectria canker. But the Nectria fungal component of the beech bark disease was not confirmed in Newmarket. The dense mass of insects on approximately 55 trees in the 3 ha woodlot indicated that the insect had been present in southern Ontario for some years.

The infested woodlots near Newmarket located about 60 km north of Toronto (Fig. 2) were comprised of co-dominant mature sugar maple and American beech trees with an understory of white ash, white birch and ironwood. It was estimated that at least 60% of the beech trees of varying ages were infested to some degree with the scale insect. There were trees with all gradations of insect and fungus injury ranging from a few small cankers with fungi to total tree mortality. Brown liquid had seeped down the trunk on heavily infested trees. The affected trees had yellow leaves with brown margins that progressed to branch and crown dieback. Some trees had an open crown appearance. Trees partially girdled by fungi and insects remain alive in a weakened state. Sporophores of Cytosporina were observed on the dead bark including fruit bodies of Hypoxylon, Stereum, Polyporus and Fomes. About 30% of these trees displayed symptoms, however no tree yielded the Nectria fungus in culture.

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Fig. 2.

Distribution of the beech bark disease in eastern North America. The Provinces and States named have reported the occurrence of the scale insect.

The observed scale insect infestation was severe and approximately 20 trees died rapidly in the two adjoining woodlots at Newmarket. The beech scale was also observed in another woodlot in King City about 30 km southwest of Newmarket. The trees at this site had similar dieback symptoms. The aftermath zone advanced by Shigo (4) could be applicable to the disease in Ontario since the bark tissue died so rapidly that conditions for sporulation of Nectria spp., which had been present previously, was now passed.

In addition, the owners who maintain the woodlots for amenity and shelter have felled and utilized the badly affected trees. Also a successful spray program using dormant superior oil + fer-bam before bud flush followed by sistox + ferbam in mid-June has been instituted during the last three years to contain the disease and control the scale insect.

We believe this to be the first documented occurrence of the beech scale insect in Ontario.

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