Which method of applying pesticides is done beneath the bark of trees?

The method of applying pesticides done beneath the bark of trees is tree injection. This technique involves injecting a pesticide directly into the tree's vascular system, allowing the chemical to be transported throughout the tree. This method is particularly effective for controlling pests that live within the tree or for addressing diseases affecting the trunk and branches.

Tree injection minimizes the chemical's exposure to non-target organisms and reduces environmental contamination, as it provides a targeted approach to pest management. It enables the active ingredient to be distributed efficiently within the tree structure, ensuring that the treatment reaches areas where pests may reside.

The other methods mentioned, such as soil application and foliar application, involve treating the soil or the leaves, respectively, and do not target the inner bark specifically. Spot treatment usually refers to localized applications on a targeted area but does not involve injecting into the tree itself. Hence, tree injection is the most appropriate method for this specific application scenario.