What distinguishes truly systemic fungicides?

Truly systemic fungicides are defined by their ability to move throughout the entire plant, including both the xylem and phloem. This characteristic allows these fungicides to be absorbed by plant tissues and distributed internally, providing comprehensive protection against fungal pathogens that may affect various parts of the plant. This systemic action means that even if the disease symptoms are not visible at the time of application, the fungicide can still work effectively by circulating through the plant and addressing any latent infections.

Additionally, systemic fungicides can provide longer-lasting protection compared to surface-active fungicides, which tend to remain on the surface where they are applied and may wash away or degrade quickly. The movement through the vascular system (xylem and phloem) ensures that the fungicide can reach areas that are otherwise inaccessible, thus enhancing its efficacy in managing disease.

The other options refer to attributes that do not apply to systemic fungicides: some may act quickly on the surface but are typically contact fungicides rather than systemic, while others may require frequent applications due to their shorter duration of effectiveness. Moreover, the reference to only working against bacteria is inaccurate since fungicides are specifically designed to combat fungal infections, not bacterial diseases.