II. Hosts: Both scale insects are important pests of peach, but other fruit and shade trees also serve as hosts. On grape, P. corni may be a pest, in addition to P. persicae (Fabr.) (introduced from Europe) and the cottony maple scale, Neopulvinaria innumerabilis (Rathvon), a North American species.
III. Description: These species are known as soft or unarmored scales since the protective covering is a thickened part of the insect's body rather than a separate structure. Adult female scales (photo above) are dark reddish-brown, often with black mottling and banding radiating down the sides. They have a very convex hemispherical shape, with a crimped margin. The terrapin scale is about 1/10 inch (2 mm) in diameter and the European fruit lecanium is slightly larger. Adult male scales are tiny 2-winged insects. Eggs of the European fruit lecanium are white, and crawlers of both species are light colored.
IV. Biology: Immature female scales overwinter on the bark of twigs and limbs, usually being more abundant on the underside. They resume feeding in the spring and mature during May. During June the terrapin scale produces crawlers, whereas the European fruit lecanium produces eggs which hatch into crawlers. Crawlers migrate to the underside of foliage to feed for about one month. Female scales return to the bark of twigs and limbs to continue feeding, whereas males usually mature on foliage and emerge to mate with females. There is one generation of the terrapin scale and one or two generations of the European fruit lecanium per year.
V. Injury: These scale species tend to be less injurious than SJS. Where infestation is severe, twig and limb death may occur as feeding scale remove sap from the tree. A more common problem is the discoloration of fruit and leaves from a black sooty mold which grows on the honeydew produced by feeding scale.
VI. Monitoring: Monitor crawler emergence with black electrician's tape wrapped around scale infested branches with the sticky side out. A thin coating of petroleum jelly will enhance and extend the tape's effectiveness in capturing crawlers. There are no thresholds for these scale insects.
VII. Control: Oil sprays are effective
terrapin scale. Recent work has included plant-based, soybean oil as an
effective alternative to petroleum oils (Pless et al. 1995).