Key Features
- Sticky blackened leaves and branches
- Black bumps with white spots
- Dead and dying branches
Symptoms
Trees infested with calico scale become covered with a sticky liquid excrement called honeydew. Heavy infestations can kill branches. Lower branches become weak or die from excessive coating with sooty mold. Branches and leaves can be coated black when honeydew gets infested with a sooty mold. Honeydew can also become a nuisance in the summer when it rains from the tree canopy and attracts stinging wasps. Calico scales are easily distinguished from other soft scales by the distinct pattern of white flecks on its black body. 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
Immature scales winter in cracks and crevices of branches and the trunk. Scales 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 when winged males fly to wingless females to mate in April. Females fill themselves with thousands 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 is most effective against actively crawling scale insects with minimal impact on beneficials. Pyriproxifen or buprofizen directed against crawler and recently settled scales can help reduce scale populations with minimal impact on the beneficials that eat scales and prevent outbreaks of spider mites. Other products listed will kill scale crawlers and beneficial insects. Bifenthrin is effective when applied on egg laying scales in the spring, but can cause outbreaks of spider mites later in the season. To protect bees, do not apply foliar insecticides when bees are flying to flowers. Applications of oil in the dormant season DO NOT control this pest. 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 receive adequate irrigation after treatment. They ultimately destroy the natural enemies that normally keep calico scale from becoming a problem. To protect bees avoid use of these products until AFTER flower production.
Effective Pesticides
Active Ingredients include: Acetamiprid, Bifenthrin, Buprofezin , Dinotefuran, Esfenvalerate, Flupyradifurone, Fluvalinate, Imidacloprid, Insecticidal soap (Potassium salt of fatty acid), Pyriproxyfen
