Key Features
- Thin elongate bumps on twigs
- Dying branches
- Loss of vigor
Symptoms
Small, gray, or brown scales on branches and twigs appear as thin, long, bumps. Japanese maple scale will readily kill branches and twigs that have become encrusted with scales. These scales are much thinner than oystershell scales. Unlike the closely related soft scales, these insects will be dry and not coated with sticky liquid excrement. All stages of this scale can be separated from the plant tissue by flipping them over with a fingernail without ripping 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, not scale insects.
Biology
Wintering as mated and immature females, eggs hatch into flat wingless insects called crawlers. Crawlers walk on stems until they settle to attach themselves to the stems and start to feed. Scales use a fine, wire-like tube to pierce plant tissue and suck its liquid contents. Soon after scales begin feeding they become translucent. Female scales remain where they have settled for the remainder of their lives. Males fly away from their feeding sites only after they have developed wings. There are two generations a year in Indiana with crawlers being found from early May through June an again from mid August through September. The prolonged crawler period makes this insect particularly difficult to control with insecticides.
Management Recommendations
Verify that scales are alive by flipping them over to look for bodies filled with pale purple fluid. Apply horticultural oil during dormant season in early spring to kill overwintered scales. This scale is very difficult to control during the growing season because the susceptible stage of crawlers is present throughout most of the summer. Two applications of horticultural oil, pyriproxifen, buprofezin, or azadirachtin in early and late June will kill crawlers but not natural enemies. Professionals have had excellent results by adding 1/2 % horticultural oil to their pyriproxifen or buprofezin crawleter sprays. Repeat in August if the scales are still alive. All other listed products will kill scale crawlers and beneficial insects. 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. To protect bees, do not apply insecticide when plants are flowering. Oil will only kill bees during the 4 hours it takes to dry after spraying.
Effective Pesticides
Active Ingredients include: Acetamiprid, Bifenthrin, Buprofezin , Cyfluthrin, Flupyradifurone, Horticultural oil (Paraffinic or superior oil) , Lambda- cyhalothrin, Neem oil, Permethrin, Pyriproxyfen
