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Oystershell scale

By: Garden Gate staff
If you think shellfish are growing on the branches and trunks of your woody shrubs and trees, you’re not seeing things.

pest watch

Oystershell scale Lepidosaphes ulmi

IDENTIFICATION – If you think shellfish are growing on the branches and trunks of your woody shrubs and trees, you’re not seeing things. Those hard, dull-brown, 1/8-inch-long caps are oystershell scale. Like all scale, they feed on sap, which can weaken or even kill a plant if their infestation is heavy.

LIFE CYCLE – Scale start as eggs, hatching in late May or early June. In their juvenile form, called crawlers, they’re the size of a pinhead and very mobile. Within a few hours of hatching, they spread out, settle down, insert their mouthparts into the plant and never move again. Within a week they’re covered with their oyster-shaped, waxy shells.

CONTROL – The shell resists insecticides. But in winter, when plants are dormant, you can smother scale with a solution of dormant oil. Spray the infestation with 8 oz. of oil to 1 gal. of water. For light infestations, remove the pests from the bark with a fine, plastic scrubbing pad. Be careful not to damage the bark. Treat crawlers with a mixture of 4 oz. lighter weight summer oil to 1 gal. of water. You can buy these oils at garden centers or home improvement stores. If a branch is completely covered with scale, your best bet is to remove the entire branch.

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