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Pesticide resistance — the inherited ability of a pest population to survive doses that previously were lethal — is one of the greatest threats to sustainable crop protection. Understanding resistance mechanisms and applying sound management principles is essential for maintaining the long-term viability of chemical pest control.
Resistance is an evolutionary phenomenon. When a pesticide is applied:
Key insight: Resistance exists in the population before the pesticide is applied — the pesticide selects for it, not creates it.
| Mechanism | How It Works | Example |
|---|---|---|
| Metabolic | Enzymes detoxify the pesticide faster | Pyrethroid resistance in fall armyworm |
| Target-site | The target protein is altered | ACCase resistance in ryegrass |
| Penetration | Thicker cuticle or waxy layer | Some organophosphate resistance |
| Behavioural | Pests avoid treated areas | Some insecticide resistance |
International resistance management committees classify pesticide modes of action into numbered groups:
The golden rule: Never apply two consecutive sprays from the same mode-of-action group.
Plan your spray programme to alternate between different groups each application. Never use the same group more than twice consecutively.
Sub-lethal doses do not kill susceptible individuals efficiently and allow partially resistant individuals to survive. Always apply the full label rate.
Only apply pesticides when pest populations exceed economic thresholds. Unnecessary applications accelerate resistance selection.
Be alert to signs of reduced efficacy:
