White waxy filaments produced by beech scale mothers protect eggs and hatching nymphs on the trunk of this American beech (J. Llewellyn)
Introduced Beech scale (Cryptococcus fagisugae) goes hand in hand with beech bark disease (Neonectria faginata and N. ditissima). It is believed that the wounds made by the tiny scale nymphs create entry points for the lethal fungal disease. Beech scale is easier to see this time of year on our native American beech (Fagus grandifolia). That’s because of the white waxy coverings the females produced to protect their eggs in late summer. Look for tiny tufts of white, cottony-like masses on the main trunk and large branches.
Beech scale NYMPHS within woolly masses on trunks and large branches of American beech (D. Cheung)
Examine trunks and large branches for white, woolly masses. Gently open up the woolly mass and use your hand lens to look for oval, yellow brown eggs or nymphs with red eyes (about 1 mm long). You will need a hand lens to see them in detail. See more images on BugFinder.
Beech Scale Crawlers (Photo: Melody Melzer, University of Guelph)
Eggs hatch from late summer to early winter, and crawlers migrate to other parts of the tree or are transported by wind to other beech trees. Once crawlers settle, they feed by inserting their stylets into the inner bark and phloem. You will notice that the crawlers prefer bark that is rough, such as cracks and crevices. These crawlers will molt and overwinter on the bark.
The nymph life stage is sensitive to horticultural oil applications while temperatures are still mild and nymphs are actively feeding. Although some horticultural oil products are listed as being phytotoxic to beech leaf tissue, a direct trunk application may be appropriate this late in the season. Re-assess beech scale viability about 10-14 days later to determine whether a second application may be necessary.
Do not apply horticultural oil at the dormant rate when there is a chance of frost.
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Some landscapers and arborists will pressure wash beech scale from the trunks this time of year. This simple cultural management practice can really help reduce the number of viable nymphs that would re-infest our beautiful beech next year.
Beech scale is quite often the precursor to Beech Bark Disease (Neonectria faginata and N. ditissima), as this scale insect feeding creates wound sites for the fungal disease to enter (photo above). The continuous formation of fungal cankers around the tree trunk eventually girdles the tree, leading to mortality.
Management of beech scale in the early stages may help suppress beech bark disease.
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