How do protectant fungicides differ from systemic fungicides?

In the context of plant pathology, protectant and systemic fungicides differ primarily in how they interact with plant tissues and provide defense against pathogens.

Protectant Fungicides

Protectant fungicides function by creating a chemical barrier on the surface of the plant. They are not absorbed or translocated through plant tissues, meaning they only protect the specific areas to which they are applied. Because they remain on the surface, they are susceptible to being removed by environmental factors such as wind, rain, or irrigation, and they can be broken down by sunlight. Furthermore, as a plant grows, new, untreated foliage remains vulnerable to infection, often necessitating repeated applications.1

Systemic Fungicides

In contrast, systemic fungicides are absorbed by the plant and distributed throughout its tissues. This allows them to provide internal protection for the plant, including for new growth that develops after the initial application. Beyond acting as a preventative measure, systemic fungicides can also function as chemotherapeutants, meaning they are capable of eradicating existing infections within the plant.12