🐛 Fungicides and Bactericides

This lesson builds core elective concepts in BSc Agriculture with practical applications and exam-oriented clarity.

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Fungicides and Bactericides

Fungicides are chemical compounds used to prevent, cure, or eradicate fungal infections in crops. Bactericides target bacterial pathogens causing diseases like bacterial blight, wilt, and canker.

Classification of Fungicides

By Mode of Action

Type	Action	Examples
Protectant (contact)	Prevent spore germination on plant surface	Mancozeb, Copper oxychloride, Chlorothalonil
Systemic (curative)	Absorbed and translocated within plant	Carbendazim, Propiconazole, Azoxystrobin
Eradicant	Kill established fungal infections	Hexaconazole, Tebuconazole
Translaminar	Move across leaf tissue	Trifloxystrobin, Pyraclostrobin

By Chemical Group

• Dithiocarbamates — multi-site action, protectant (Mancozeb, Zineb, Thiram)
• Benzimidazoles — tubulin assembly inhibition (Carbendazim, Thiophanate-methyl)
• Triazoles (DMIs) — ergosterol biosynthesis inhibition (Propiconazole, Hexaconazole, Tebuconazole)
• Strobilurins (QoIs) — mitochondrial respiration inhibition (Azoxystrobin, Trifloxystrobin)
• Copper-based — multi-site protectant (Bordeaux mixture, Copper hydroxide, Copper oxychloride)
• Phenylamides — RNA polymerase inhibition (Metalaxyl, Metalaxyl-M)
• SDHIs — succinate dehydrogenase inhibition (Fluxapyroxad, Boscalid)

FRAC Classification

The Fungicide Resistance Action Committee (FRAC) groups fungicides by mode of action:

• Multi-site (M) — low resistance risk (dithiocarbamates, copper)
• Single-site — higher resistance risk (triazoles, strobilurins, benzimidazoles)
• Alternation and tank-mixing of different FRAC groups is recommended

Bactericides

Bacterial diseases are harder to control chemically. Key bactericides include:

• Streptomycin sulphate (Streptocycline) — antibiotic used at 500 ppm for bacterial blight and soft rot
• Copper oxychloride — effective against both fungal and bacterial pathogens
• Kasugamycin — used for rice blast and bacterial diseases
• Bordeaux mixture — lime and copper sulphate combination, one of the oldest and most effective

Application Methods

• Foliar spraying — most common method for contact and systemic fungicides
• Seed treatment — Thiram, Carboxin, or Trichoderma-based products for seed-borne pathogens
• Soil drenching — Metalaxyl or Carbendazim for soil-borne diseases (damping off, root rot)
• Trunk injection — for perennial crops with vascular infections

Key Considerations

• Apply protectant fungicides before disease onset for best results
• Systemic fungicides are effective even after initial infection
• Avoid repeated use of single-site fungicides to prevent resistance buildup
• Integrate fungicide use with cultural practices and resistant varieties

Rational use of fungicides and bactericides, guided by disease forecasting and FRAC guidelines, ensures effective disease management while minimizing environmental impact.

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Summary Cheat Sheet

Topic	Key takeaway
Main focus	Fungicides and Bactericides — classification, mode of action, systemic and contact fungicides, and usage in crop protection.
Section context	Revise this lesson with the rest of Synthetic Pesticides for stronger conceptual continuity.