Key Features
- Dead twigs and branches
- Oyster shaped bumps on branches
- Leaf drop
Symptoms
Small, gray or brown scales shaped like oyster shells are present as bumps on branches and twigs. These scales are much thicker than Japanese maple scales. Oystershell scale will readily kill branches and twigs that are encrusted with scales. Unlike the closely related soft scales, these insects will be dry and not coated with a sticky liquid excrement. All stages of this scale can be separated from the plant tissue by flipping them over with a fingernail. This flipping process will not rip the the plant surface. If you remove a bump on a plant and the tissue rips, this means the plant has produced a gall or swelling in response to an insect or disease. This is not caused by scale insects.
Biology
Scales winter as eggs beneath the scale cover of a female, eggs hatch into crawlers in May after black locust is in full bloom. Eggs hatch into a wingless stage called a crawler that walks on stems until finding a place to feed. Once feeding commences, these insects become flattened and clear and are known as settled crawlers. This insect feeds on plants by piercing stem tissue with a fine, wire-like tube that it uses for its mouth. This slender tube will penetrate plant tissue much like a plumber's snake as it destroys a plant tissue while feeding. This species of scale can kill stems and branches when leaves are encrusted with large numbers of scales. A second generation of crawlers is produced from late July to early August. Partial third generations occur in some years.
Management Recommendations
Scale insects have many natural enemies including lady beetles, lacewings and stingless wasps. Consider pruning out heavily infested branches in the winter. This species of scale is not controlled by oils in the dormant season because it winters in the egg stage.Verify that scales are alive in early May or late July by flipping them over to look for bodies filled with fluid before deciding to apply insecticide. Foliar sprays of pyriproxifen, buprofizen, neem oil, or azadirachtin can be quite effective against crawling and settled stages of scales with minimal impact on natural enemies that help control this pest. Other products listed will kill beneficial insects and scales. Monitor for periods of crawler activity by wrapping scale infested twigs or branches with a single band of black electrical tape so the sticky side faces out. Crawlers that emerge from scales are easy to see when they get stuck in the glue. Oil will only kill bees during the 4 hours it takes to dry after spraying.
Effective Pesticides
Active Ingredients include: Acetamiprid, Azadirachtin, Bifenthrin, Buprofezin , Cyfluthrin, Dinotefuran, Flupyradifurone, Horticultural oil (Paraffinic or superior oil) , Lambda- cyhalothrin, Neem oil, Permethrin, Pyriproxyfen
