What happens to most systemic herbicides after application?

Most systemic herbicides are designed to be absorbed by the plant and then translocate throughout its tissues. Once applied, these herbicides penetrate the plant's cellular structure and move through the plant's vascular system, allowing them to affect areas that are not directly contacted during the application. This internal movement is essential for the herbicide to disrupt physiological processes, ultimately leading to the plant's death or impaired growth.

The effectiveness of systemic herbicides stems from their ability to reach the root systems or other vital parts of the plant, enabling a thorough treatment of the target species. This characteristic is particularly advantageous when controlling perennial weeds, which may have deep root systems or extensive rhizomes.

The other responses refer to behaviors that are not representative of systemic herbicides: staying on the surface of leaves would limit their effectiveness, quick evaporation would reduce their efficacy, and frequent reapplications are typically unnecessary when the herbicide is systemic and well-absorbed.