Managing Calico scale (Hemiptera: Coccidae) infestations on landscape trees

Calico scale, Eulecanium cerasorum (Cockerell), an invasive pest of shade trees, has reached outbreak levels in landscapes and on horse farms in Kentucky, U.S. We evaluated efficacy and timing of conventional and reduced-risk foliar insecticides as well as trunk-injected or soil-applied systemics for managing E. cerasorum. Acephate, bifenthrin, carbaryl, cyfluthrin, and pyriproxyfen killed young settled crawlers on individually sprayed shoots. Whole-canopy pyrethroid sprays, however, gave <66% control, underscoring the difficulty of reaching settled crawlers within large shade trees. Horticultural oil and insecticidal soap were relatively ineffective even with full spray coverage. Preventive sprays with bifenthrin or pyriproxyfen in mid-May, at first egg hatch, intercepted crawlers before they settled on leaves. Dormant oil failed to control overwintered nymphs or reduce subsequent numbers of adults or crawlers. A plant antitranspirant applied in late March provided 33% suppression. Trunk-injected imidacloprid was ineffective, whereas dicrotophos (bidrin) gave at best <50% control. Soil injection with imidacloprid in November, December, or March failed to reduce subsequent densities of adults on branches or crawlers on leaves. Reasons why it is difficult to eliminate calico scale in mature landscape trees are discussed in the context of the pest's feeding sites and behavior.