• Latin Name: Lapidosaphes ulmi
  • Latin Family Name: Diaspididae
  • Common Name: Oystershell Scale
  • Other Names: Apple mussel scale

Origin:
Thought to have originated in temperate Eurasia, but now found throughout the world.

Biology:
Major host plants include ash, aspen, cottonwood, lilac, maple, poplar, willow, apple, and dogwood, but over 130 kinds of trees or shrubs in the U.S. are known hosts. The various forms of the scale are given names like lilac form, brown form, banded form, gray form, or apple form. There appears to be a single generation in northern states but possibly two generations in southern states. Where there is one generation the female deposits her eggs under her wax cover in the late summer and fall, and then overwinters. The crawlers emerge in mid-spring and after moving around for a short period will then settle onto one spot, insert their mouthparts, and remain there. As they molt they lose their legs. The shed skins are incorporated into the wax covering, which develops the classic “oyster shell” shape, of elongated, narrow at the front end, and widened at the posterior.

Identification:
Adult females may be from 1 mm to 3.5 mm in length, and are colored silvery gray or light brown, turning to darker purplish or brown as they age. They form a classic oyster or mussel shell shape, very narrow at one end and tapering much wider at the other, with the narrow end a contrasting orange color.

Characteristics Important to Control:
This scale has the potential to develop massive infestations on bark of shrubs and trees, with dead scales’ wax covers remaining on the plant for several years, leading to entire areas of the bark covered by them. Heavy feeding cause loss of plant health, dieback of twigs, cracking of bark, and overall decline in the appearance of the plant. Where populations of the scale warrant control dormant or summer oils may be effective, as well as contact insecticides applied when the first instar crawlers are present. An IGR applied when crawlers are present also may be effective.