Classification by Mobility: Contact vs Systemic Fungicides
Fungicides are fundamentally divided based on whether they remain on the plant exterior or penetrate internal vascular tissues.
- Contact (Protective) Fungicides: Form a protective chemical shield on the plant surface, preventing fungal spore germination; examples include Mancozeb, Copper Oxychloride, and Sulphur.
- Systemic (Curative) Fungicides: Absorbed through foliage and translocated acropetally or basipetally via the xylem or phloem to halt established infections; examples include Hexaconazole, Carbendazim, and Metalaxyl.
- Translaminar Fungicides: Penetrate through the leaf cuticle to protect both upper and lower leaf surfaces; examples include Azoxystrobin, Pyraclostrobin, and Cymoxanil.
- Combination Formulations: Premixes of contact and systemic actives (e.g., Metalaxyl + Mancozeb, Iprovalicarb + Propineb) that provide simultaneous external protection and internal curative action.
Major Chemical Classes and Scientific Examples
Understanding key chemical families enables farmers and agronomists to rotate modes of action and manage fungicide resistance.
- Dithiocarbamates (FRAC M03): Broad-spectrum multi-site contact inhibitors; prominent examples include Mancozeb, Propineb, and Zineb.
- Triazoles / DMIs (FRAC 3): Ergosterol biosynthesis inhibitors; widely used examples include Tebuconazole, Hexaconazole, Difenoconazole, and Propiconazole.
- Strobilurins / QoIs (FRAC 11): Mitochondrial respiration inhibitors; major examples include Azoxystrobin, Pyraclostrobin, and Trifloxystrobin.
- SDHIs (FRAC 7): Succinate dehydrogenase inhibitors; high-potency examples include Fluxapyroxad, Boscalid, and Fluopyram.
- Phenylamides (FRAC 4): Specific anti-oomycete agents targeting RNA polymerase; classic example is Metalaxyl.
- Biological Fungicides: Formulated with antagonistic living microorganisms; prominent examples include Trichoderma viride and Bacillus subtilis.
Application Best Practices and Resistance Management
Over-reliance on single-site systemic fungicides promotes the rapid selection of resistant fungal strains.
- FRAC Rotation Protocol: Never apply fungicides from the same FRAC mode-of-action group for more than two consecutive rounds in a single cropping cycle.
- Incorporate Multi-Site Actives: Tank-mix or alternate single-site systemic actives with multi-site contact protectants like copper or mancozeb.
- Preventive Application: Initiate treatments preventively or at the earliest economic threshold level before widespread sporulation occurs.
- Statutory Compliance: Follow all dosage guidelines, pre-harvest waiting periods, and PPE instructions mandated on registered CIBRC container labels.
Official source
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Central Insecticides Board & Registration Committee (CIBRC) ↗Related on KisanPe
Common questions
What is the difference between contact and systemic fungicides?
Contact fungicides remain on the outer leaf surface to prevent spore germination, whereas systemic fungicides penetrate into plant tissues to halt established infections.
What are some common examples of systemic fungicides?
Common systemic fungicides include Hexaconazole, Tebuconazole, Azoxystrobin, Carbendazim, Difenoconazole, and Metalaxyl.
Why is Mancozeb considered ideal for fungicide resistance management?
Mancozeb is a multi-site contact inhibitor that disrupts multiple fungal metabolic pathways simultaneously, making it virtually impossible for fungi to develop single-gene resistance.
General guidance, not personal advice. For your farm, ask your local Krishi Vigyan Kendra or agriculture officer.
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