Systemic fungicides are chemical compounds that protect plants from fungal diseases by working from within. Unlike treatments that remain on the surface, these fungicides are absorbed by the plant and move throughout its internal systems. This allows them to offer a more thorough and lasting defense against various fungal infections.
Internal Action within Plants
Systemic fungicides enter plants through roots, leaves, or seeds. Once absorbed, they are transported throughout the plant via its vascular system. This movement primarily occurs through the xylem, which carries water and nutrients upwards from the roots, and sometimes through the phloem, which distributes sugars and other organic compounds, including to new growth.
This translocation allows them to reach newly formed leaves, stems, and other parts not directly sprayed, providing protection as the plant grows. Once inside, systemic fungicides interfere with the invading fungi’s biological processes. Their mechanisms vary, often disrupting fungal cell wall synthesis, inhibiting respiration, or interfering with enzyme activities needed for fungal growth and reproduction. For example, some target ergosterol biosynthesis, unique to fungal cell membranes, while others inhibit nucleic acid metabolism or protein synthesis within fungal cells.
Advantages of Systemic Protection
The internal distribution of systemic fungicides offers several advantages for plant protection. A primary benefit is the protection of new, untreated growth, as the fungicide moves into developing tissues, ensuring continuous defense. This internal presence also means the fungicide is less susceptible to being washed off by rain or irrigation, offering more consistent disease control.
Systemic fungicides also offer prolonged residual activity compared to surface-acting treatments. This extended protection reduces application frequency, saving time and resources. Their ability to move within the plant provides thorough protection, even reaching areas difficult to cover with external applications.
Responsible Application and Environmental Considerations
Proper application of systemic fungicides is essential for both effectiveness and environmental safety. Following label instructions for dosage and timing ensures the fungicide works as intended and minimizes the risk of fungicide resistance development in fungal populations. Applying the correct amount at the right time helps achieve optimal disease control while avoiding overuse.
Fungicide resistance is a concern, as fungi can evolve mechanisms to overcome chemical effects. To mitigate this, strategies like rotating different active ingredients are employed. This involves alternating fungicides with different modes of action to prevent widespread resistance to a single chemical type. Environmental impacts also require consideration; improper use can affect non-target organisms like beneficial insects or soil microbes. Runoff into water sources is another concern, emphasizing the need for proper disposal of unused fungicides and their containers to prevent contamination.
Systemic vs. Contact Fungicides
Systemic fungicides differ from contact fungicides in their mode of action and how they protect plants. Contact fungicides, also known as protective fungicides, remain on the plant surface where applied. They form a barrier that prevents fungal spores from germinating or penetrating plant tissue, with protection limited to directly covered areas.
In contrast, systemic fungicides are absorbed and translocated internally, providing protection throughout the plant’s vascular system. This internal movement allows them to protect new growth and offer some curative action against existing infections, which contact fungicides generally cannot. Contact fungicides are typically preventive, requiring reapplication as new growth emerges or after heavy rain, while systemic fungicides offer a more enduring internal defense.