Forest Pests: Insects, Diseases & Other Damage Agents

Oystershell Scale
Lepidosaphes ulmi (L.)

Hanson, T., and E. B. Walker. [n.d.] Field guide to common insect pests of urban trees in the Northeast. Waterbury, VT: Department of Forests, Parks and Recreation.

Homoptera: Diaspididae Hosts: Beech, birch, maple, ash, poplar, willow, elm, lilac, apple, pear, cherries and many other plants. Evidence: Look for tiny brown to gray oystershell-shaped scales, usually densely packed, on the bark (a, b). Foliage may appear thin and chlorotic and there may be areas of the crown that lack leaves or where there are scattered clumps of leaves. Life Cycle: The life cycle varies with the host tree species. In general, insects overwinter in the egg stage in groups of 50-100 under the scale cover. Crawlers emerge in May and move to feeding sites on twigs and branches. Adult females are present in July. By late July, they have formed a scale covering beneath which the white eggs are laid.

a. Infestations are usually confined to twigs and branches.

b. The "armor" of the Oystershell scale may be lifted to expose a tiny legless adult female or a batch of eggs.

Management: This insect tends to cover entire branches before populations spread to a new area of the host tree. If scales are heavy enough to cover branches, host dieback is likely to result. Branches that are heavily infested should be pruned out. Known enemies include lady beetles, parasitic wasps, and mites. Additional control measures are often needed. Dormant oils are effective against overwintering populations, and systemic or contact insecticides can be used to control crawlers. Summer oils may also be effective.

Photo Credits:

Figure a: E. Bradford Walker, Vermont Department of Forests, Parks and Recreation, Waterbury, VT.

Figure b: E. Bradford Walker, Vermont Department of Forests, Parks and Recreation, Waterbury, VT.

References:

Drooz, A.T. 1985. Insects of Eastern Forests. USDA Forest Service Miscellaneous Publication 1426. p 114-115,

Johnson, W.T. and Lyon, H.H. 1991. Insects That Feed on Trees and Shrubs. 2nd edition. Cornell University Press. p 370-371;

Martineau, R. 1984. Insects Harmful to Forest Trees. Agriculture Canada Government Publishing Centre, Supply and Services, Ottawa. p 206;

Rose, A.H. and Lindquist, O.H. 1997. Insects of Eastern Hardwood Trees. Canadian Forest Service Publication, Forestry Technical Report 29. p 229.

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