What does "systemic" indicate when referring to a pesticide?

When the term "systemic" is used in relation to a pesticide, it specifically refers to its ability to be absorbed by a plant or organism and then move throughout its tissues. This means that after the pesticide enters the plant, it can distribute itself within the vascular system, effectively reaching locations where pests may not be able to make contact with it directly, such as the interior of leaves or stems. This characteristic allows systemic pesticides to provide more comprehensive protection against pests that feed on the plant, as they can affect pests that consume any part of the treated plant, even those that do not come into direct contact with the pesticide at the time of application.

In contrast, other options do not accurately describe systemic properties. Immediate effectiveness pertains to contact herbicides which act quickly upon application but do not necessarily have systemic movement. Residual properties refer to how long a pesticide remains effective after application in the environment, which does not relate to its ability to move within a plant. Similarly, stability in varying weather conditions addresses the physical and chemical attributes of the pesticide itself, not its internal movement within a biological system.