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

The correct choice is microinjection, which refers to the method of delivering pesticides directly into a plant or tree through a small opening, such as a drilled hole. This technique allows the pesticide to be introduced directly into the vascular system of the tree, ensuring it is effectively absorbed and distributed throughout the plant tissues. Microinjection is advantageous in that it minimizes the exposure of the pesticide to the environment and targets the specific area where pest control is needed.

Systemic application, while it involves delivering pesticides that are absorbed into the plant and transported throughout its tissues, typically includes methods like foliar sprays or soil applications that lead to uptake through roots or leaves. Soil drench involves applying pesticides to the soil to be absorbed by the roots, while granular application refers to the distribution of pesticide granules on the surface of the soil or plant, where they dissolve slowly.

Each of these other methods differs significantly in their approach to pesticide application compared to microinjection, making microinjection the distinct choice for delivering pesticide through a drilled hole in a tree.