Characteristics of Pesticides

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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
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Pesticide Names
There are three names associated with every
pesticide

• Chemical name

Common name
Product name
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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

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Names in the R8 Label Book Summary Sheets

• Common names
• Brand names
• (If the chemical name is needed see the label
  not the summary sheet)

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Another Caution ---Pronunciation of Names

• FORAY
• 4-AA
• PHORATE

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Some quick definitions
Solution Suspension - Emulsion - Invert
Emulsion
Bypass definitions
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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
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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
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Some quick definitions
Solution Suspension Emulsion Invert
emulsion
Mixed can separate
Dissolved Does not separate
Oil droplets in water
Water droplets in oil
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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

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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

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Classification of Organic Herbicides by Chemistry

• Phenoxy herbicides
• Triazines
• Imidazolinone
• Sulfonylureas

Bypass details
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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

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Classification of Organic Insecticides by
Chemistry

• Chlorinated hydrocarbons
• Organophosphates
• Carbamates

Skip definitions
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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

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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

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Amine Ester

• Organic salt

• Oil based

• Water soluble

• Oil soluble or can be emulsified in water

• Low volatility

• High volatility

• Low toxicity for fish

• High toxicity for fish

• Bark or foliar applications

• Injection cut-surface treatments

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LD50s of field formulations
Triclopyr LD50 630 mg/kg
Garlon 4 --LD50 1,419 mg/kg
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LD50s of field formulations
Garlon 4 --LD50 1,419 mg/kg
Streamline uses a 17 solution of Garlon 4 gt
1,419 / 0.17 8,347 mg/kg Foliar spray is
normally done as a 3 solution gt 1,419 / 0.03
47,300 mg/kg
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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

• Toxicity to humans and wildlife
• Application timing
• Weaknesses or limitations

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

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The following slides discuss these and several
other properties of pesticides in
generalDiscussion in the R-8 Label Book
section (later this week) presents chemical
specific information
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Mode of Action Herbicides

• Movement in the plant
• Contact
• Translocated
• Action in the plant
• Inhibit protein synthesis, photosynthesis, or
  growth

Bypass definitions
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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
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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

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Mode of Action Life Stage Affected

• Ovicide
• Larvicide
• Adulticide

Bypass Definitions
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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

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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

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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

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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

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Soil Mobility

• A major contributor to offsite movement
• Leaching vs. lateral movement
• Affected by the soils
• Sand content
• Clay content
• Organic matter content
• Affects chemical half-life but not the degradation

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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)

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Persistence/Degradation Process Drivers

• Temperature
• Relative humidity / Rainfall
• pH
• Insolation
• Soil or water biota
• Macrophytes
• Microbial populations
• Worms and microfauna

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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

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Toxicity to Humans and Wildlife

• Varies by chemical
• Based on the target biochemistry of the product
• Much more later in this session

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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

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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

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Weaknesses and Limitations

• Repeats environmental concerns
• Toxicological/health concerns
• Lists formulation specific concerns such as
  flammability
• Lists use restrictions

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Environmental behavior More thoughts not in
specific categories in the label book
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Off-site movement
Lots of differing processes involved
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Pesticide Movement Degrade

• Runoff
• Leaching
• Degradation
• Microbial
• Physical
• Hydrolysis
• Photolysis
• Pyrolysis
• Volatilization

Bypass definitions
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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

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Breakdown generalizations

• Hotter temperature faster breakdown
• Higher relative humidity faster breakdown
• More microbes faster breakdown
• pH effect chemical dependant
• More slope more runoff

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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