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Extension > Garden > Insects > Scale insects on Minnesota trees and shrubs > Scale insects that feed on deciduous trees: Armored Scales

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Scale insects that feed on deciduous trees: Armored Scales

Wayne Seidel, University of Minnesota Extension

Figure 14. Oystershell scales on a flowering crabapple.

Oystershell Scale

Lepidosaphes ulmi

Appearance: Purplish-gray, about 1/8 inch (3 mm) long and shaped like tiny oyster shells (Figure 14).

Hosts: Lilac, apple, poplar, birch, ash, cotoneaster, willow and many other deciduous trees and shrubs.

Damage: Feeding by the scales causes cracked bark and chlorotic, stunted foliage. Heavy infestations can kill trees or weaken them to the point of being susceptible to secondary pests such as borers.

Life history: Overwinter as eggs beneath the dead mother scale. Crawlers hatch in late May to early June and seek suitable feeding sites on branches and trunks. Nymphs mature in mid-summer to mate. Eggs are laid in late summer to early fall beneath the mother's scale. There is one generation per year.

Management: Systemic management using dinotefuran as a soil application or as a bark treatment is effective when applied in the spring. Insecticidal soaps, horticultural oils, insect growth regulators (pyriproxifen and buprofezin [available only to licensed applicators]), and residual insecticides (such as pyrethroids, acephate, and carbaryl) can be applied to treat the crawler stage. Timing of these applications when the crawlers are active is crucial for effective control. Combining systemic treatment with a crawler spray will provide the most effective control.

Manuel Jordán, Heritage Shade Tree Consultant

Figure 15. Scurfy scale on the trunk of a quaking aspen.

Scurfy Scale

Chionaspis furfura

Appearance: Females are flat, pear-shaped, dirty whitish-gray and about 1/8 inch (3 mm) long. Males are similar in appearance but smaller (Figure 15).

Hosts: Crabapple, poplar, birch, mountain ash, cherry, plum and many other deciduous plants.

Damage: Feeding by the scales can cause twig and branch dieback and weaken plants.

Life history: Overwinter as eggs beneath the dead mother scale on branches and trunks. Crawlers appear in June and begin feeding on leaves, branches and trunks. Nymphs mature in August, mate and lay overwintering eggs. There is thought to be one generation per year in Minnesota, but a second generation may occur.

Management: Insecticidal soaps, horticultural oils, insect growth regulators (pyriproxifen and buprofezin [available only to licensed applicators]), and residual insecticides (such as pyrethroids, acephate, and carbaryl) can be applied to treat the crawler stage. Timing of these applications when the crawlers are active is crucial for effective control. Systemic management using dinotefuran as a soil application or as a bark treatment is effective when applied in the spring. Combining systemic treatment with a crawler spray will provide the most effective control.


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