Formulations, Modes of Action and Resistance Management
A formulation is the active ingredient plus carriers and adjuvants. Know the trade-offs:
- Emulsifiable concentrate (EC): solvent-based, mixes to a milky emulsion, good coverage, but solvents can cause phytotoxicity and damage rubber or plastic, and are more irritating and flammable.
- Wettable powder (WP): clay-carried powder; needs constant agitation, leaves visible residue, clogs filters, and the dust is a mixing hazard.
- Water-dispersible granule (WDG) / soluble powder (SP): much less dust, easier to measure, still needs agitation.
- Suspension concentrate / flowable (SC): pre-ground particles, less solvent, needs agitation.
- Dusts, granules, baits: dry and ready to use; granules need moisture to release; bait placement matters more than coverage.
- Microencapsulated: slow release; hazardous to bees, which collect capsules like pollen.
- Fumigants: gases requiring sealing, buffer zones and specialized certification.
Mode of action classification (IRAC for insecticides, FRAC for fungicides, HRAC for herbicides) groups products by the site where they act. Resistance management is built on MoA rotation: alternate different groups across generations, use full label rates, tank-mix partners with different MoA, and add non-chemical tactics. Higher rates accelerate resistance.
Traps: rotating between two products that are both Group 3 pyrethroids - same MoA, no benefit; and raising the rate to beat a failing product.
Worked example: greenhouse whiteflies survive repeated Group 4 (neonicotinoid) and Group 3 (pyrethroid) sprays. The correct response is to switch to a different MoA group plus biological and cultural controls - not to raise the rate or add another pyrethroid.