Whitney Cranshaw, Colorado State University, Bugwood.org
Parthenolecanium fletcheri (Cockerell)
The Fletcher scale, sometimes referred to as the arborvitae soft scale, is a common pest of arborvitae, Thuja spp. and yew, Taxus spp. It has also been reported to attack juniper, Juniperus spp., cypress, Cupressus spp., and hemlock, Tsuga spp. Occasionally, Fletcher scale is sometimes confused with the European fruit lecanium. Host plant association may provide assistance in accurate identification since Fletcher scale usually attacks arborvitae and especially yew.
Eggs hatch into oval, flat, amber to yellow first instar nymphs called crawlers. Adult females are yellowish brown to tan, almost hemispherical, and about 2-4 mm in diameter (Fig. 1). Males are unknown for this species.
Figure 1. Mature female Fletcher scale on yew.
This pest overwinters as second instar nymphs. They develop rapidly in the spring. Adult females normally are found on the twigs and stems of the host plant. Females start laying eggs in late May. One female may deposit an average of 500-600 eggs. These hatch in June into crawlers that migrate a short distance on a branch in search of a feeding site. They remain on the host plant for the remainder of the season. This species reproduces by parthenogenesis. One generation is produced each growing season in Pennsylvania.
This pest can reduce the health of an infested plant by removing plant fluids. This soft scale insect secretes an abundance of honeydew (sticky, sugar-rich material). In addition, heavily infested plants may become unsightly by a heavy crust of black sooty mold that develops on the honeydew. Heavily infested yews may have chlorotic (yellow) needles or drop them prematurely.
Overwintering second instar nymphs may be managed with a dormant rate of horticultural oil applied according to label directions in early spring before new growth occurs and after the danger of freezing temperatures has passed. Apply registered insecticides according to label directions against the crawler stage from June through mid-July. Repeat applications may be needed. Malathion may injure 'canaerti' juniper. Soil injection or drenching with a registered systemic insecticide labeled for management of this pest may also be applied according to label directions. Early spring application of these registered formulations usually works best against this species when sufficient soil moisture exists. Prior to applying one of these systemic products, applicators may need to irrigate around an infested plant to provide adequate soil moisture.
Pesticides are poisonous. Read and follow directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams, or ponds.
Authored by: Gregory A. Hoover, Sr. Extension Associate
Revised December 2006