Characteristics of Pesticides Basic concepts relating to the names, chemistry, mode-of-action and fate of pesticides Edited for general use by: Vincent Mannino, CED-Fort Bend

Pesticide Names There are three names associated with every pesticide: 1.Chemical name 2.Common name 3.Product/Trade 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 pesticide 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 4A

Caution --- Pronunciation of Names FORAY 4-AA PHORATE

Some quick definitions  Solution  Suspension  Emulsion  Invert Emulsion

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 Example

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

Some quick definitions Emulsion A suspension of small droplets of an oil- based or an ester pesticide in water

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 Formulations Liquids –Solutions –Emulsifiable Concentrates –Ultra Low Volume Concentrates –Low Volume Concentrates –Aerosols –Liquefied gas Solids –Dusts –Granules –Pellets –Soluble Powders –Wettable Powders –Flowables –Baits

Gross Classification of Pesticides by Chemistry Inorganic pesticides Organic pesticides Biological pesticides

Gross Classification of Pesticides by Chemistry Inorganics –Molecules that do not contain carbon Heavy metals – lead and arsenic Copper products Sulfur products

Gross Classification of Pesticides by Chemistry Organics –Molecules contain carbon May be chains or rings Carbon containing molecules are broken down by micro-organisms Organics included botanicals and man-made chemical formulations that include carbon compounds

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

Classification of Organic Herbicides by Chemistry Phenoxy herbicides – 2,4-D, 2,4-DP, 2,4,5-T – Behaves as an auxin causing hypertrophy (increase in cell size) – Sample structure

Classification of Organic Herbicides by Chemistry Triazines – Hexazinone – Have extreme soil mobility – Structure

Classification of Organic Herbicides by Chemistry Imidazolinone – Imazapyr – Structure

Classification of Organic Herbicides by Chemistry Sulfonylureas – Metsulfuron & sulfometuron methyl – Sample structure

Classification of Organic Insecticides by Chemistry Chlorinated hydrocarbons Organophosphates Carbamates Skip definitions

Classification of Organic Insecticides by Chemistry Chlorinated hydrocarbons – Dieldrin, aldrin, DDT, mirex, chlordane – Sample structure Return

Classification of Organic Insecticides by Chemistry Organophosphates – Malathion, azinphos-methyl, naled – Sample structure Return

Classification of Organic Insecticides by Chemistry 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 Return

Esters (General Characteristics) Oil based Oil soluble / can be emulsified in water Generally highly volatile Highly toxic to fish Used for bark & foliar applications

Characteristics Amine vs. Ester Organic salt –Water soluble –Low volatility –Low toxicity to fish –Injections & cut surface treatments Oil based –Oil soluble or can be emulsified in water –High volatility –High toxicity to fish –Bark or foliar applications

LD 50 s of field formulations Garlon 4 --LD 50 1,419 mg/kg

LD 50 s of various products Comparison of oral LD50 (values for common herbicides and consumer goods) HerbicideLD 50 Consumer goodsLD 50 Paraquat (Gramoxone)~100Nicotine9 Triclopyr630Caffeine192 2,4-D666Bleach192 Pendimethalin (Prowl)1,050Tylenol338 Atrazine3,090Household Ammonia350 Glyphosate4,900Codeine427 Imazaquin (Image)>5,000Table Salt3000 LD 50 is the lethal dose that will kill 50% of the test animals in milligrams of product to kilograms of test animals body weight

LD 50 s of field formulations Garlon 4 --LD 50 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: Mode of action Selectivity Soil activity and mobility Persistence and breakdown Toxicity to humans and wildlife Application timing Weaknesses or limitations

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 misapplied to include only foliar applied herbicides which move downward from the leaves to the roots Return

Contact Poisons Systemic Poisons Attractants –Phermones –Baits Repellents

Mode of Action: Contact Insecticide Pesticide which causes injury or death of insect through the touch rather than through inhalation or ingestion Return

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 – kills the eggs Larvicide – kills the immatures Adulticide – kills the adults

Mode of Action: Life Stage Affected Ovicide - Kills eggs

Mode of Action: Life Stage Affected Larvicide - Kills larval stage (immature) insects

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 Many newer products are more selective Application method also influences selectivity (soil applied vs. foliar applied)

Soil Activity Soil Active Herbicide: applied to the soil. These chemicals are readily absorbed by plant roots or underground plant shoots, and subsequently negatively affects the plant in some manner

Soil Activity Non-Soil Active Herbicide: applied to 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 & 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 (visible plant life) –Microbial populations –Macrobes (worms, nematodes, etc)

Persistence & 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

Off-site movement processes

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 flooding rain

Pesticide Movement & Degrade Leaching –Also called percolation – the process whereby pesticide is moved down through the soil profile

Pesticide Movement & Degrade Microbial Degradation –Breakdown of pesticides by fungi, bacteria and other microscopic organisms

Pesticide Movement & Degrade Physical Degradation –Hydrolysis -- Breakdown of a pesticide by water

Pesticide Movement & Degrade Physical Degradation –Photolysis – breakdown of a pesticide by sun or other light

Pesticide Movement & Degrade Physical Degradation –Pyrolysis – the breakdown of a pesticide by heat or fire

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 dependent More slope = more runoff More organic matter = more tie-up

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

Questions?