📈 Fungicide Application Methods and Resistance Management

Effective fungicide use depends not only on selecting the right chemical but also on how and when it is applied. Equally critical is the management of fungicide resistance, which threatens the longevity of these valuable tools.

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Application Methods

Seed Treatment

• Dry seed treatment — fungicide powder dusted onto seeds (e.g., thiram at 2-3 g/kg seed)
• Slurry treatment — fungicide mixed with a small volume of water to coat seeds
• Pelleting — seed coated with a polymer containing fungicide, insecticide, and nutrients
• Protects against seed-borne and soil-borne pathogens during germination

Foliar Spraying

The most common method. Fungicide is diluted in water and applied using:

Equipment	Scale	Coverage
Knapsack sprayer	Small farms	Low to moderate
Power sprayer	Medium farms	Good
Boom sprayer	Large farms	Uniform
Aerial spraying	Plantation crops	Extensive

Spray timing is guided by disease forecasting models, growth stage, and weather conditions. Proper nozzle selection, spray volume, and droplet size ensure adequate coverage.

Soil Drenching

Fungicide solution is poured at the base of plants to control root and collar rot pathogens. Common for nursery beds and high-value crops. Examples include carbendazim drench for Fusarium wilt and metalaxyl for Pythium damping-off.

Other Methods

• Trunk injection — for systemic management of vascular wilts in trees
• Post-harvest dipping — fruits dipped in fungicide solutions to prevent storage rots
• Fumigation — enclosed spaces treated with volatile fungicides (e.g., formaldehyde for soil sterilization)

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Fungicide Resistance

How Resistance Develops

• Single-site fungicides exert strong selection pressure on pathogen populations
• Resistant mutants that survive treatment reproduce and dominate the population
• High-risk groups include benzimidazoles (point mutation in beta-tubulin), QoIs (G143A mutation in cytochrome b), and phenylamides

Anti-Resistance Strategies

• Rotate fungicides with different FRAC codes — never apply the same mode of action consecutively
• Tank-mix a single-site fungicide with a multi-site protectant (e.g., azoxystrobin + mancozeb)
• Limit the number of applications per season for high-risk fungicides (typically 2-3 sprays)
• Use fungicides only when necessary — threshold-based application reduces selection pressure
• Monitor populations for resistance using bioassays or molecular diagnostics

Resistance Management in Practice

Strategy	Implementation
Alternation	Spray triazole in first application, strobilurin in second
Mixture	Combine SDHI + multi-site in a single spray
Restriction	Maximum two QoI applications per crop season
Integration	Combine with resistant varieties and cultural control

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Principles of Rational Fungicide Use in IPDM

• Fungicides are a supplement, not a substitute, for other management practices
• Apply at the correct growth stage and disease development phase
• Follow label recommendations for dosage and pre-harvest interval
• Choose formulations with minimal environmental impact
• Maintain records of fungicide use for resistance monitoring

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Summary Cheat Sheet

Application Methods

Method	Best Use Case
Seed treatment	Early protection from seed and soil-borne pathogens
Foliar spray	Aerial disease management during crop growth
Soil drench	Root-zone and collar infections
Post-harvest dip	Storage rot reduction

Resistance Essentials

• Rotate FRAC groups and avoid repeated single-mode sprays.
• Use mixtures with a multi-site partner where appropriate.
• Apply only on need-based thresholds to reduce selection pressure.

Exam Traps

• Right fungicide with wrong timing can still fail.
• Repeated use of one high-risk chemistry speeds resistance.
• Resistance management is weak without seasonal spray records.

References

2 sources • [1] [2]

[1]

FRAC fungicide resistance management guidelines

Website

[2]

ICAR crop protection recommendations

Official