Ch.3: About Pesticides

2. Types of pesticides (by what they control / mechanism)

3. Four ways to group pesticides

A. EPA pesticide groups (three broad categories):

1. Conventional — synthetic (manufactured) chemicals other than antimicrobials/biopesticides; also include attractants, repellents, plant-growth regulators, defoliants; most commonly used.
2. Antimicrobial — destroy/suppress harmful microorganisms (bacteria, viruses, fungi) on inanimate, non-living objects/surfaces. A fungicide on a living crop is not antimicrobial — it's applied to a living surface.
3. Biopesticides — derived from natural materials (plants, bacteria, fungi, certain minerals). EPA subcategories: Biochemical, Microbial, Plant-Incorporated Protectants.

B. Regulatory category (from Ch.1): RUPs, General Use (unclassified), Minimum risk (25b).

C. Chemical family — members share a similar chemical structure → often similar properties (toxicity, persistence). But slight structural differences can change properties.

D. Mode of action — the specific way a pesticide affects a pest (e.g., disrupts nervous system vs. interferes with hormones). Important for managing pesticide resistance (Ch.11).

Most common grouping overall: by the types of pests they manage.

4. Pesticide properties

Most properties are inherent to the molecule's chemistry/structure and can't be changed — though certain adjuvants can increase or decrease some.

Selectivity — how broad or narrow a range of organisms a pesticide controls.

• Broad-spectrum (nonselective) — affects a wide range of species; useful against several pests at once (e.g., carbaryl, glyphosate). Downside: can harm nontarget species.
• Narrow-spectrum (selective) — controls only a few, usually related pests without harming others; may target a life stage (larva vs. adult) or feeding habit (chewing vs. piercing-sucking). Upside: may spare beneficials like bees.

Route of entry — contact or systemic (some do both).

• Contact — controls a pest when it physically touches it (direct spray, or crossing a treated surface). A contact herbicide kills a weed by covering enough surface to stop photosynthesis.
• Systemic — applied to one area, then moves (translocates) through the plant/animal to harm the pest. Can also protect (e.g., a topical flea/tick product absorbed into a pet).

Persistence (= residual activity) — how long it stays active.

• Highly persistent → controls pests weeks, months, or years; nonresidual → breaks down quickly into nontoxic by-products.
• Long persistence risk: more time to move off-target, enter the food supply, contaminate ground/surface water, or harm nontarget organisms.
• Depends on: the chemical's rate of degradation + environmental factors (temperature, pH, moisture).

Volatility — tendency to turn into a gas/vapor; increases with higher temperatures. Volatile products may carry label limits: downwind buffer zones, or no application above a set temperature/wind speed.

Solubility — ability to dissolve in a liquid (usually water).

• Upside: highly soluble products generally don't need agitation in the tank.
• Risk: more likely to move with surface runoff (→ streams, lakes) or leach downward through soil (→ groundwater).

Sorption — one substance becomes attached to or mixed in with another; covers absorption and adsorption (AB vs. AD).

• Absorption — movement of the chemical into plants, animals, soil, or wood (paper towel soaking up water).
• Adsorption — the pesticide binds to soil particles (paper clips to a magnet). Strongly adsorbed → less runoff/leaching, but also less available to control pests.

Key Vocabulary