Pest Management and Pesticide Use (Core)
Start with the pest, not the product
Every core question ultimately asks whether you can justify a treatment decision. Know the vocabulary cold: pest (any organism causing damage or nuisance), economic threshold (the pest density at which control cost equals the value of loss prevented), action threshold (the density triggering treatment, usually at or below the economic threshold), and integrated pest management (IPM) - a decision framework that combines monitoring, sanitation, cultural, mechanical, biological, and chemical tactics, using pesticides only when thresholds justify them.
Labels and modes of action
Understand that the label is the legal document, and that resistance management depends on rotating mode-of-action groups (IRAC/HRAC/WSSA group numbers), not just product names. Traps: two products with different brand names may share a group number; tank mixes of the same group do not count as rotation. Also know selectivity (narrow- vs. broad-spectrum), systemic vs. contact activity, residual length, and formulation differences (EC, WP, WDG, SC, bait) and how each affects mixing and phytotoxicity risk.
Pest biology drives timing
Questions often hinge on life stage: target larvae when small, treat weeds at the seedling stage, treat perennials when carbohydrate flow moves downward, and remember that dormant treatments and pre-emergent timing depend on pest and host phenology. Know the difference between contact, residual, fumigant, repellent, and growth-regulator actions and match the tactic to the target.
Worked rule of thumb
If a field has an average of 4 larvae per sample and the action threshold is 3, treatment is justified. If the same sampling shows 60% parasitized larvae, effective density is about 1.6 healthy larvae per sample - below threshold - so hold and re-scout. Always scout before spraying and re-scout after.
Common traps
Confusing economic with action threshold; assuming a spray kills all life stages; ignoring beneficials; treating on a calendar rather than on scouting data.