Ability of Ant Exclusion via Basal Trunk Insecticide Sprays and Insecticidal Baits to Sustainably Manage Soft Scale Insect Infestations in Urban Landscape Trees

Soft scale insects are common pests of many urban tree species that are difficult to manage. Soft scales suck sap from tree phloem which can worsen tree condition. As soft scales feed they excrete honeydew which supports the growth of unsightly sooty mold on surfaces below trees. Arborists commonly address scale insect infestations by applying systemic neonicotinoid insecticides to trees, often with variable efficacy. Additionally neonicotinoids can become sequestered into tree pollen at concentrations toxic to pollinators. Such effects are concerning since scales are common pests of many tree species that attract pollinators such as red maple, saucer magnolia, and crape myrtle. Additionally, systemic neonicotinoids are becoming increasingly restricted for use throughout the United States which is reducing the options available for arborists to treat scale infestations. Another common treatment approach for soft scales entails applications of broad-spectrum contact insecticides when scale crawlers are emerging, however such interventions require precise timing, multiple applications, and can kill beneficial insect taxa such as natural enemies (predators and parasitoids) or pollinators. Overall, arborists need novel intervention tactics to sustainably manage scale insects in urban trees while minimizing off-target effects on beneficial insects. Ants feed on honeydew produced from soft scale herbivory and ants protect scales from natural enemies which would otherwise regulate scale populations. Excluding ants from trees with sticky bands can increase scale biological control by natural enemies, but these effects are short term, and bands can injure wildlife, and often appear unsightly to residents. Application of insecticides or insecticidal baits around the base of trees may exclude ants from tree canopies long term with fewer off-target effects to wildlife and aesthetics in comparison to sticky bands. Contact insecticide application to the base of trees may reduce scale insect populations without off-target effects on beneficial insects observed in systemic neonicotinoid treatments or foliar sprays of broad spectrum insecticides. In this project we will determine which insecticides and insecticidal baits applied to the base of trees can exclude ants from scale-infested trees, the duration of these effects, and resultant impacts on scale population reduction via increased biological control by natural enemies. The overarching goals for this project are to create sustainable and effective management guidelines for soft-scale insects in landscape trees.