What is a characteristic of systemic pesticides?

Systemic pesticides are distinct in their ability to be absorbed by plants and then translocate throughout the entire plant. This characteristic allows them to treat not only the pests that are directly on the plant's surface but also those that may be feeding on different parts, including the roots, leaves, and stems. The absorption process means that once the pesticide enters the plant’s vascular system, it can provide protection and control against a broader range of pests over time.

The other options imply functions and characteristics that do not align with the fundamental nature of systemic pesticides. For instance, discussing only surface-level effects or exclusive uses for weeds misrepresents the broader applicability and effectiveness of systemic formulations against various pests, including insects and some diseases. Additionally, while some systemic pesticides may require reapplication based on specific pest pressures or environmental conditions, this is not universally true for all systemic products, nor is it a defining characteristic of this type of pesticide.