Soil injections of imidacloprid are frequently used to control insect pests on trees

Soil injections of imidacloprid are effective at preventing attack by the walnut twig beetle, a very aggressive beetle that will attack both healthy and stressed trees. Imidacloprid can also be injected directly into the trunk or soil so there is no public contact. Soil injections of imidacloprid are also very effective against Elm leaf beetles, a cyclic pest, European elm scale, one of the most widespread and destructive scale insects, Hawthorn mealybug and Kermes scale, which affects pin oak and red oak trees.

Source: City of Boulder, Colorado
http://www.bouldercolorado.gov/index.php?option=com_content&task=view&i…