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Fletcher Scale

June 13, 2001

Fletcher scale, Parthenolecanium fletcheri, is a common pest in nurseries and on sheared hedges in landscapes. This scale feeds on arborvitae (Thuja spp.) and yews (Taxus spp.) and has been known to feed on Pachysandra. On yews they are generally located deep within the plant canopy. The female scales are approximately 1/4 inch long, round, and deep brown in color when mature. In Illinois, eggs produced by females hatch between May and early July into oval, flat, yellowish crawlers. Females can lay around 500 to 600 eggs and are capable of producing up to 1,000 eggs. Crawlers are active from mid-June to mid-July. They tend to congregate and feed on twigs and stems deep within the plant canopy. Fletcher scale feeding weakens plants, causing foliage to drop. They also produce copious amounts of honeydew, which is an excellent growing medium for black sooty mold fungi. There is one generation per growing season.

Fletcher scale can be managed using pest control materials including acephate (Orthene), chlorpyrifos (Dursban), diazinon, insecticidal soap, and summer oil. Applications should be made in mid-June when crawlers are active or when hills of snow hydrangea are in full bloom because the early crawlers are most susceptible to insecticides. Be sure that sprays penetrate the entire plant canopy.

Natural enemies may cause rapid declines in Fletcher scale populations because many predators are effective in controlling nymphs. As a result, use insecticides that are less harmful to natural enemies. Avoid the use of broad-spectrum insecticides that kill the natural enemies of Fletcher scale.

Author: Raymond A. Cloyd


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