Key Features
- Sticky black leaves and branch
- Sooty mold
- Dusty white bumps on branches
Symptoms
Trees infested with magnolia scales have twigs crusted with large, dust coated bumps up to 1/2" in diameter. Scales produce a sticky excrement called honeydew than can coat leaves and branches, turning them black with an unsightly sooty mold. Honeydew begins to accumulate significantly after females mate with males in mid-June and continues throughout the summer and may cause a nuisance by attracting stinging wasps. Heavy accumulations of honeydew and sooty mold can kill branches. 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 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 and is not a scale insect. Tuliptree scale is a smaller, orange insect that can cause similar problems with honeydew and sooty mold on magnolias. Be sure to compare what you see with the pest description for Tuliptree scale.
Biology
Wintering as immature scales on twigs, they resume feeding when the plant comes out of dormancy in the spring. Winged males emerge in June and mate with females. Females can produce over 3,000 eggs that hatch into black crawlers in late August and September. Crawlers migrate to and settle on stems. Immature scales winter on stems.
Management Recommendations
Insecticidal soap directed against crawlers in August and September can help reduce scale populations with minimal impact on beneficials. Pyriproxifen or buprofizen directed against crawler and recently settled scales can also reduce scale populations with minimal impact on the beneficials. Other products listed will kill scale crawlers and beneficial insects. Oil applied in the dormant season will NOT control this pest. Fall applications of foliar insecticides avoids problems with bees. Soil applied systemic insecticides (imidacloprid and dinotefuran) can kill maturing the scales on a tree, and stop the rain of honeydew within several weeks after application if trees receive proper irrigation. To protect bees avoid use of these soil insecticides until AFTER flower production but not in fall against the crawling stage.
Effective Pesticides
Active Ingredients include: Bifenthrin, Buprofezin , Esfenvalerate, Flupyradifurone, Fluvalinate, Insecticidal soap (Potassium salt of fatty acid), Lambda- cyhalothrin, Neem oil, Pyriproxyfen
