Characteristics of Pesticides

Basic concepts relating to the names, chemistry, behavior and fate of Pesticides including a review of the R8 Label Book summary pages

Pesticide Names

Chemical name *

Common name *

Product name *

There are three names associated with every pesticide

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definitions

Pesticide Names:Chemical Name

The systematic Name of a Chemical Compound according to the rules of nomenclature of the International Union of Pure and Applied Chemistry as adapted for indexing in Chemical Abstracts

For example: 3,5,6-trichloro-2-pyridinyloxyacetic acid.. is a chemical name

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Pesticide Names:Common Name

A generic name for a chemical compound (see the Weed Science Society of America list of herbicide nomenclature)

For example: The common name for 3,5,6-trichloro-2-pyridinoxyacetic acid.. is triclopyr

The common name is the name generally used in discussing pesticidal toxicology and environmental behavior and fate

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Pesticide Names:Product Name

The trade name of a pesticide; that is the name on the container you purchase. It is also the name to which the EPA registration number is applied at the time of registration

Triclopyr alone is sold as: Garlon 3A or Garlon 4

Names in the R8 Label BookSummary Sheets

• Common names

• Brand names

• (If the chemical name is needed – see the label not the summary sheet)

Another Caution ---Pronunciation of Names

FORAY

4-AA

PHORATE

Some quick definitions

Solution *

Suspension *

- Emulsion *

- Invert Emulsion *

Bypass definitions

Some quick definitions

Solution

A liquid or solid chemical which is dispersed completely (not suspended) in water or another fluid. For our purposes this includes water solutions and ester or other oil-soluble chemical dissolved in oil

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Some quick definitions

Suspension

Finely divided solid particles or liquid droplets dispersed (but not dissolved) in another solid, a liquid or a gas.

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Some quick definitions

Emulsion

A suspension of small droplets of an oil-based or an ester pesticide in water

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Some quick definitions

Invert Emulsion

A suspension of small droplets of water in an oil. Some chemicals are now produced as invert emulsions

Some quick definitions

Invert Emulsion

Generally the formation of an invert emulsions is undesirable. Without special precautions during mixing and use they commonly form resulting, in a sludge of the approximate consistency of mayonnaise that clogs hoses and nozzles and creates a major problem of clean-up

Some quick definitions

Solution Suspension

Emulsion Invert emulsion

Oil droplets in water

Water droplets in oil

Dissolved –Does not separate

Mixed – can

separate

Types of Product Formulation

• Liquids– Solutions– Emulsifiable

concentrates– Ultra Low Volume

Concentrates– Low Volume

Concentrates– Aerosols– Liquified gas

• Solids– Dusts– Granules– Pellets– Soluble Powders– Wettable Powders– Flowables– Baits

Gross Classification of Pesticides by Chemistry

• Inorganic pesticides *

• Organic pesticides *

• Biological pesticides *

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Gross Classification of Pesticides by Chemistry

• Inorganics – Molecules do not contain carbon

• Heavy metals – lead and arsenic• Copper products• Sulfur products

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Gross Classification of Pesticides by Chemistry

• Organics – Molecules contain carbon

• May be chains or rings

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Gross Classification of Pesticides by Chemistry

• Biologicals– Viruses, bacteria, fungi, and plants– Nematodes, insects and other parasites or

predators

Classification of Organic Herbicides by Chemistry

• Phenoxy herbicides *

• Triazines *

• Imidazolinone *

• Sulfonylureas *

Bypass details

Classification of Organic Herbicides by Chemistry

• Phenoxy herbicides – 2,4-D, 2,4-DP, 2,4,5-T– Behaves as an auxin causing hypertrophy– Sample structure

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Classification of Organic Herbicides by Chemistry

• Triazines – Hexazinone– Have extreme soil

mobility– Structure

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Classification of Organic Herbicides by Chemistry

• Imidazolinone – Imazapyr

– Structure

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Classification of Organic Herbicides by Chemistry

• Sulfonylureas – Metsulfuron & sulfometuron methyl– Sample structure

Classification of Organic Insecticides by Chemistry

• Chlorinated hydrocarbons *

• Organophosphates *

• Carbamates *

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Classification of Organic Insecticides by Chemistry

• Chlorinated hydrocarbons – Dieldrin, aldrin, DDT, mirex, chlordane– Sample structure

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Classification of Organic Insecticides by Chemistry

• Organophosphates – Malathion, azinphos-methyl, naled– Sample structure

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Classification of Organic Insecticides by Chemistry

• Carbamates – Carbaryl (Sevin)– Structure

2 Basic Chemical Groups for Herbicides

Amines *

Esters *

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AmineGeneral Characteristics

• Organic salt• Water soluble• Low volatility• Low in its toxicity to fish• Used for injection & cut-surface

treatments

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Esters(General Characteristics)

• Oil based

• Oil soluble / can be emulsified in water

• Generally highly volatile

• Highly toxic to fish

• Used for bark & foliar applications

Amine Ester

• Organic salt • Oil based

Injection & cut-surface treatments

Low toxicity for fish

Low volatility

Water soluble

Bark or foliar applications

High toxicity for fish

High volatility

Oil soluble or can be emulsified in water

LD50s of field formulations

Garlon 4 --LD50 1,419 mg/kg

Triclopyr – LD50 630 mg/kg

LD50s of field formulations

Garlon 4 --LD50 1,419 mg/kg

Streamline uses a 17% solution of Garlon 4 => 1,419 / 0.17 = 8,347 mg/kg

Foliar spray is normally done as a 3% solution => 1,419 / 0.03 = 47,300 mg/kg

Environmental behavior:Several categories of environmental

behavior are included in the summaries which precede each chemical presented in the Region-8 Label Book

Information includes:

• Mode of action• Selectivity• Soil activity and mobility• Persistence and

breakdown

• Toxicity to humans and wildlife

• Application timing• Weaknesses or

limitations

The following slides discuss these and several other properties of pesticides in general

Discussion in the “R-8 Label Book” section (later this week) presents chemical specific information

Mode of Action:Herbicides

• Movement in the plant– Contact *– Translocated *

• Action in the plant– Inhibit protein synthesis, photosynthesis, or growth

Bypass definitions

Mode of Action:Contact Herbicide

One which causes injury to only the plant tissue to which it is applied, or one which is not appreciably translocated within a plant

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Mode of Action:Translocated Herbicide

One which is moved within a plant from the point of application to the point of action; may be either phloem-mobile or xylem-mobile

The term is often misapplied to include only foliar applied herbicides which move downward from the leaves to the roots

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Mode of Action: Animal Poisons (incl. Insecticides)

Contact poison *

Systemic poison *

Attractants * Pheromones Baits

Repellants * Bypass definitions

Mode of Action:Contact Insecticide

Pesticide which causes injury or death of insect through the touch rather than

through inhalation or ingestion

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Mode of Action:Systemic Insecticide

Pesticide which is moved within a plant from the point of application to the point where the insect will contact or ingest it

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Mode of Action:Attractants

Pesticide which lures animals to a predetermined spot– Pheromones are biochemicals either released by

the animal or synthesized which are sex attractants – Baits are chemicals which entice animals for

reasons other than sex (smells like food)

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Mode of Action:Repellants

Pesticide which discourages animals from coming to a specific area

– Many chemicals unrelated to sexual activity (due to smell or other physical characteristic) are repellant to animals

– Pheromones in low concentration are attractive to animals but, often, in high concentration become repellant

Mode of Action:Life Stage Affected

Ovicide *

Larvicide *

Adulticide *

Bypass

Definitions

Mode of Action:Life Stage Affected

Ovicide

– Kills eggs

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Mode of Action:Life Stage Affected

Larvicide

– Kills larval stage (immature) insects

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Mode of Action:Life Stage Affected

Adulticide

– Kills adult insects

Mode of Action:Selectivity

• Many products express a degree of selectivity – Extremely variable from product to product– Biologicals often more selective than chemicals

• Despite claims, selectivity is generally limited– Often based on rate

• Many newer products are more selective• Application method also influences selectivity

Soil Activity

Soil Active Herbicide: applied to or present in the soil, these chemicals are readily absorbed by plant roots and subsequently negatively affects the plant in some manner

Soil Activity

Non Soil Active Herbicide: applied to or present in the soil, these chemicals are bound to soil particles or organic matter and are essentially unavailable to affect plants

Soil Mobility

• A major contributor to offsite movement• Leaching vs. lateral movement• Affected by the soil’s

– Sand content– Clay content– Organic matter content

• Affects chemical half-life but not the degradation

Persistence and Degradation

• Persistence – The resistance of a herbicide to metabolic or environmental degradation or removal; a measure of the duration of retention of activity by a pesticide in the environment

Degradation – The breakdown of a substance into simpler molecular or atomic components through chemical reaction(s) either in a plant or animal (metabolic degradation) or in the environment (environmental degradation)

Persistence/Degradation:Process Drivers

• Temperature• Relative humidity / Rainfall• pH• Insolation• Soil or water biota

– Macrophytes– Microbial populations– Worms and microfauna

Persistence and Degradation: Half-Life

The time required for half the amount of a substance (such as a herbicide) present in or introduced into a system (living or ecological)

to be eliminated, whether by excretion, metabolic degradation, off-site transport, or

other natural process

Toxicity to Humans and Wildlife

• Varies by chemical

• Based on the target biochemistry of the product

• Much more later in this session

Primary Forestry Uses

• Discussion of silvicultural and other uses

• And, of methods of application

• Appropriate for the formulation(s) of the pesticide available for use

• Much more later

Application timing

• Product specific

• May also relate to formulation

• Gives a measure of selectivity

• Discussed for each pesticide and formulation

• Summarized in the Label Book in a comparative table for all herbicides

Weaknesses and Limitations

• Repeats environmental concerns

• Toxicological/health concerns

• Lists formulation specific concerns such as flammability

• Lists use restrictions

Environmental behavior:

More thoughts not in specific categories in the label book

Off-site movement

Lots of differing processes involved

Pesticide Movement & Degrade

• Runoff *• Leaching *• Degradation

– Microbial *– Physical

– Hydrolysis *– Photolysis *– Pyrolysis *

• Volatilization *Bypass

definitions

Pesticide Movement & Degrade

• Runoff – movement of pesticide aboveground in water –

generally occurs downslope but can also occur on flat or even slightly uphill ground after a flloding rain

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Pesticide Movement & Degrade

• Leaching– Also called percolation – the process whereby pesticide is

moved down through the soil profile

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Pesticide Movement & Degrade

• Microbial Degradation– Breakdown of pesticides by fungi, bacteria and other

microscopic organisms

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Pesticide Movement & Degrade

• Physical Degradation– Hydrolysis -- Breakdown of a

pesticide by water

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Pesticide Movement & Degrade

• Physical Degradation– Photolysis – breakdown of a pesticide by

sun or other light

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Pesticide Movement & Degrade

• Physical Degradation– Pyrolysis – the breakdown

of a pesticide by heat or fire

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Pesticide Movement & Degrade

• Volatilization – evaporation of a heated pesticide

Breakdown generalizations

• Hotter temperature = faster breakdown

• Higher relative humidity = faster breakdown

• More microbes = faster breakdown

• pH effect = chemical dependant

• More slope = more runoff

Off-site movement generalizations

• More clay and organics = less leaching• Higher temperature = more volatilization• Lower relative humidity = more volatilization• Higher wind speed = more volatilization and

drift• Nearer to moving water = higher probability of

contamination and off-site movement• Finer droplets = more movement