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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.


Pesticide Names

There are three names associated with every pesticide:

  • Chemical name *
  • Common name *
  • Product name *

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.


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.


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 Book Summary 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 – 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
  • Suspension – Finely divided solid particles or liquid droplets dispersed (but not dissolved) in another solid, a liquid or a gas
  • Emulsion – A suspension of small droplets of an oil-based or an ester pesticide in water
  • Invert Emulsion – A suspension of small droplets of water in an oil. Some chemicals are now produced as invert emulsions
    Generally the formation of an invert emulsion is undesirable. Without special precautions during mixing and use they commonly form resulting in a sludge of the approximate consistentcy of mayonnaise that clogs hoses and nozzles and creates a major problem of clean-up

Solution – Dissolved - Does not separate Suspension – Mixed - Can separate
Emulsion – Oil droplets in water Invert Emulsion – Water droplets in oil

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 *

Inorganics

  • Molecules do not contain carbon
    • Heavy metals – lead and arsenic
    • Copper products
    • Sulfur products

Organics

  • Molecules contain carbon
  • May be chains or rings

Biologicals

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

Classification of Organic Herbicides by Chemistry

  • Phenoxy herbicides *
  • Triazines *
  • Imidazolinone *
  • Sulfonylureas *


Phenoxy herbicides

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



Triazines

  • Hexazinone
  • Have extreme soil mobility
  • Structure



Imidazolinone

  • Imazapyr
  • Structure



Sulfonylureas

  • Metsulfuron & sulfometuron methyl
  • Sample structure


Classification of Organic Insecticides by Chemistry

  • Chlorinated hydrocarbons *
  • Organophosphates *
  • Carbamates *

Chlorinated hydrocarbons

  • Dieldrin, aldrin, DDT, mirex, chlordane
  • Sample structure

Organophosphates

  • Malathion, azinphos-methyl, naled
  • Sample structure

Carbamates

  • Carbaryl (Sevin)
  • Structure

2 Basic Chemical Groups for Herbicides

  • Amines *
  • Esters *

Amine
(General Characteristics)

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

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

  • Organic salt
    • Water soluble
    • Low volatility
    • Low toxicity for fish
    • Injection & cut-surface treatments

Ester

  • Oil based
    • Oil soluble or can be emulsified in water
    • High volatility
    • High toxicity for fish
    • Bark or foliar applications


LD50s of field formulations


Triclopyr – LD50 630 mg/kg



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 limitationsc

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

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.


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 mis-restricted to mean a foliar applied herbicide which moves downward from the leaves to the roots.


Mode of Action: Animal Poisons (incl. Insecticides)

  • Contact poison *
  • Systemic poison *
  • Attractants *
    • Pheromones
    • Baits
  • Repellants

Mode of Action: Contact Insecticide

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


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 .


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…)

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 *

Ovicide

  • Kills eggs
 

Larvicide

  • Kills larval stage (immature) insects
 

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.


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 and
  • Toxicological/health concerns
  • Also lists formulation specific concerns such as flammability, and
  • 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 *


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

Leaching

  • Also called percolation – the process whereby pesticide is moved down through the soil profile


Microbial Degradation

  • Breakdown of pesticides by fungi, bacteria and other microscopic organisms



Physical Degradation

  • Hydrolysis - Breakdown of a pesticide by water
  • Photolysis – breakdown of a pesticide by sun or other light
  • Pyrolysis – the breakdown of a pesticide by heat or fire
  • 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
  • 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

[  Contents  ]

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The University of Georgia - Warnell School of Forestry and Natural Resources and
College of Agricultural and Environmental Sciences - Dept. of Entomology
Last updated on Wednesday, November 06, 2002 at 09:58 AM
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