Key Features
- Brown bumps on twigs
- Sticky honeydew
- Yellow bumps on leaves
Symptoms
Trees infested with lecanium scales become covered with a sticky liquid excrement called honeydew. Heavy infestations can kill branches. Scales produce a sticky excrement called honeydew than can coat leaves and branches, turning them black with an unsightly sooty mold. The excrement also becomes a nuisance in the summer when they attract stinging wasps. Lecanium scales are dark brown in color. 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.
Biology
These two species of scales and their close relatives attack a wide variety of plants and have a similar life cycle. Immature scales winter on stems. They begin to grow and expand as the weather warms in the spring and the sap begins to rise in the trees. They become adults in early spring and the winged males fly to wingless females to mate in April. Females fill themselves with hundreds of eggs that hatch into a wingless, crawling stage in late May when Washington Hawthorn is in full bloom. These crawlers walk to leaves where they settle down to feed on leaf sap and produce liquid excrement for the duration of the summer. By the end of the summer, just prior to leaf drop, the scales walk back to the stems where they spend the winter.
Management Recommendations
Insecticidal soap directed against crawlers can help reduce scale populations with minimal impact on beneficials. Pyriproxyfen, and buprofizen can also be effective against the crawling stage of this pest even soon after it has settled on leaves without harming beneficials. Other products listed will kill scale crawlers and beneficial insects. Oil applied in the dormant season or against crawlers will NOT control this pest. To protect bees, do not apply foliar insecticides when bees are flying to flowers. Soil applied systemic insecticides (imidacloprid and dinotefuran) can kill the scales on a tree and stop the rain of honeydew within several weeks after application if trees are irrigated. These products ultimately destroy the natural enemies that normally keep the pest from becoming a problem. To protect bees avoid use of these soil insecticides until AFTER flower production.
Effective Pesticides
Active Ingredients include: Acetamiprid, Bifenthrin, Buprofezin , Dinotefuran, Flupyradifurone, Fluvalinate, Imidacloprid, Insecticidal soap (Potassium salt of fatty acid), Pyriproxyfen
