What type of pesticide delivery system is represented by introducing pesticide into the tree through a boron drill hole?

The option representing the introduction of pesticide into a tree through a boron drill hole is microinjection. This method involves using specialized equipment to directly inject a pesticide solution into the tree’s vascular system. By doing so, the pesticide is quickly distributed throughout the plant's tissues, providing effective control of pests and diseases that may be present.

Microinjection is particularly beneficial as it allows for precise application, minimizing the amount of pesticide needed and reducing the risk of environmental exposure. This method can effectively target specific areas within the tree, ensuring that the pesticide reaches the intended site of action.

In contrast, systemic application involves applying pesticides in a way that allows the plant to uptake the chemical through its roots or leaves but does not typically involve a drilling method. Soil drench involves applying pesticides to the soil so that they can be absorbed through the plant roots, while granular application disperses pesticides in solid form over the soil surface, relying on water or soil disturbance to activate the pesticide. Each of these methods differs significantly from microinjection, which is designed for direct delivery into the plant's tissue.