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 *
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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-2pyridinyloxyacetic 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 3,5,6trichloro-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 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 *
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 oilsoluble 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 oilbased 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
Dissolved –Does
not separate
Mixed –
can
separate
Oil droplets
in water
Water droplets
in oil
Emulsion
Invert emulsion
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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definitions
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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definitions
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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details
Amine
General 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

Water soluble

Oil soluble or can be
emulsified in water

Low volatility

High volatility

Low toxicity for fish

High toxicity for fish

Injection & cut-surface
treatments

Bark or foliar
applications
LD50s of field formulations
Triclopyr – LD50 630 mg/kg
Garlon 4 --LD50 1,419 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:
•
•
•
•
• Toxicity to humans and
Mode of action
wildlife
Selectivity
Soil activity and mobility • Application timing
• Weaknesses or
Persistence and
limitations
breakdown
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 xylemmobile
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