HPIPM:Pesticide Characteristics

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Authors: Whitney S. Cranshaw & Frank B. Peairs[1]

A pesticide is any substance sold to kill, retard, repel or attract a pest species. Pesticides can be classified according to their target, according to their function, or according to their chemistry.

Target Classification

Pesticide Type	Target
Bactericide (sanitizers or disinfectants)	bacteria
Defoliant	crop foliage
Desiccant	promote crop drying as a harvest aid
Fungicide	fungi
Herbicide	plants
Insecticide	insects
Miticide (or acaricide)	mites and ticks
Molluscicide	slugs and snails
Nematicide	nematodes
Plant growth regulator	growth processes of crop plants
Plant incorporated protectant (PIP)	transgenic event for insecticidal protein
Rodenticide	rodents
Wood preservative	wood destroying organisms

Functional Classification

Type	Function
Contact	kill by contact with pest
Eradicant	effective after infection by pathogen
Fumigants	enter pest in gas state
Nonselective	poisonous to both crop and weed
Post‑emergence	effective when applied after crop or weed emergence
Pre‑emergence	effective when applied after planting and before crop or weed emergence
Preplant	effective when applied prior to planting
Protectants	effective when applied before pathogen infects plant
Selective	poisonous only to weed
Soil sterilant	poisonous to all vegetation
Stomach poison	kills animal pests after ingestion
Systemic	absorbed and moved through crop or pest

Chemical Classification

Pesticides can be either organic (contain carbon) or inorganic. Most of today's pesticides are organic chemicals.

Commonly used inorganic pesticides include copper fungicides, lime‑sulfur used to control fungi and mites, boric acid used for cockroach control, and ammonium sulfamate herbicides.

Organic insecticide can either be natural (often extracted from plants or bacteria) or synthetic. Most pesticides used today are synthetic organic chemicals. They can be grouped into chemical families based on their structure and mode of action in the pest. Important chemical families of fungicides and insecticides are presented here.

Chemical Families Of Insecticides and Miticides

Chlorinated hydrocarbon insecticides (including dicofol, endosulfan, lindane and methoxychlor) were used widely after World War II, but mostly they have been discontinued due to environmental and health concerns.

Organophosphate insecticides (including parathion, disulfoton, phorate, and chlorpyrifos) are another older family that is still widely used. This group includes both contact and systemic insecticides. They are not as persistent as chlorinated hydrocarbon products but tend to be more toxic to applicators and wildlife. The organophosphate insecticides are nerve poisons and have been involved in most serious human pesticide poisonings.

Carbamate insecticides (including aldicarb, carbofuran, carbaryl, and methomyl) are nerve poisons with effects similar to those of organophosphate insecticides, but their effects are more readily reversible. Carbamates tend to be quite soluble in water and some are systemic in plants.

Pyrethroid insecticides (including bifenthrin, cyfluthrin, esfenvalerate, and permethrin) are related to pyrethrins, a naturally occurring insecticide. They are typically used at rates of active ingredient that are several times lower than organophosphate and carbamate insecticides. They generally exhibit low mammalian toxicity but are highly toxic to fish and other cold blooded organisms.

Neonicotinoids (including imidacloprid, thiamethoxam and clothianidin) were developed more recently and are modeled after nicotine. Use rates are similar to those of pyrethroid insecticides. They have low mammalian toxicity, have low to moderate environmental persistence, and are toxic and repellent to birds.

Chemical Families of Fungicides

Organic sulfur compounds (including ferbam, meteram, and thiram) are the most important family of fungicides in current use. The organic sulfur fungicides are all protectants.

Benzene fungicides (including chlorothalonil and PCNB) also are used as protectants.

Benzimidazole fungicides (including benomyl, thiabendazole, and thiophanate methyl) have been the most important group of eradicant fungicides. They also are used to prevent post‑harvest rots and as soil‑drench treatments.

Sterol inhibitor fungicides (including bayleton and banol) are a newer family. They are systemic in the plant and have eradicant activity.

Antibiotics

Antibiotics are substances such as streptomycin, tetracyclines, and avermectins, produced by one organism that are toxic to another organism. Most antibiotics in current use are product of bacteria‑like soil organisms known as actinomycetes. Antibiotics are used in medicine as well as in pest management.

Pesticide Formulations

Pesticides are formulated (combined with inert or non‑pesticidal ingredients) in various ways to improve such characteristics as handling, persistence on foliage, safety, ease of application, and ability to mix with water. There are many different formulation types. Some of those commonly used are described below.

Emulsifiable concentrates (EC or E) use emulsifiers to allow insoluble pesticides to be applied in water. Emulsifiable concentrates penetrate skin more readily than other formulations, and many of the inert ingredients are harmful to the eyes. These formulations are easily damaged in storage by exposure to extreme temperatures.

Wettable powders are pesticides formulated on dry particles that will suspend in water. These formulations require continuous agitation during application. They may cause increased wear on spraying equipment. They may also pose increased hazard during mixing because they can be easily inhaled during mixing.

Dry flowables or water dispersible granules are replacing many wettable powders due to increased ease of handling and reduced hazard during mixing. They also suspend in water, but require less agitation than wettable powders and are less abrasive. Flowable formulations are used with pesticides that can be produced only in solid or semi‑solid form. They are often ground into a fine powder and suspended into a liquid.

Soluble powders are dry formulations of pesticides that dissolve in water. Few pesticides are water soluble. They may also be formulated as liquids.

Dusts are pesticides formulated on particles designed for dry application. Dust formulations have lost popularity because of equipment difficulties, excessive drift, hazards to honeybees, and applicator inhalation hazard.

Granules are pesticides formulated on large particles of various materials. They are generally less hazardous than liquids and dusts, and have few drift problems.

Microencapsulated pesticides are impregnated into tiny, slow release plastic beads and mixed into a liquid. This formulation reduces dermal toxicity and increase residual efficacy.

Adjuvants Adjuvants are added ingredients that increase the effectiveness of the active ingredient and make application easier. These include:

Wetting agents or surfactants are used to improve spread of a spray mixture on foliage. Surfactants are most commonly used to apply pesticides on plants that have waxy or hairy leaves.

Stickers improve the weatherability of a spray deposit, particularly from washing by rainfall or irrigation.

Synergists increase the activity of insecticides by blocking the ability of the insect to break down the insecticide.

Penetrants increase uptake of herbicides into a plant.

Buffers decrease breakdown of pesticides in alkaline water.

Mixtures of Pesticides

Pesticides can be mixed with other pesticides or with fertilizers if the resulting mixture does not reduce safety or effectiveness. Incompatible mixtures can increase the toxicity or hazard of the pesticides to the applicator, the crop, or the environment for physical or chemical reasons. Undesirable physical changes may cause materials to precipitate as a solids, formation of separate layers, or other visible effects. Undesirable chemical changes may result in new compounds that increase environmental hazards, reduce the amounts of active ingredients, or cause plant injury.

Pesticide Safety

Since pesticides are poisons designed to destroy pest species, there are many hazards associated with their use. Pesticides can harm humans in different ways. Exposure to pesticides can be through the skin, mouth, eyes or lungs. Hazards to nontarget organisms and environmental contamination also are important concerns.

All pesticides should be handled with care to avoid unnecessary exposure.
The label is designed to ensure safe use, so be sure to always read understand and follow all label instructions.
Use pesticides only when they are necessary.
Use the protective equipment indicated on the label and make sure that this equipment is clean and in proper working order.
Make sure that application equipment is properly calibrated and in good working order.
Take precautions to avoid unnecessary drift during application.
Use pesticides that have low volatility.
Use formulations that resist drift and volatility.
Use low pressures during spraying.
Use nozzles which reduce formation of small spray particles.
Use high water volumes during application.
Apply pesticides close to the crop or soil surface.
Avoid applying pesticides when the temperature is high.
Avoid applying pesticides during windy conditions.
Use drift‑reducing adjuvants.
Take precautions to avoid contamination of surface and groundwater.
Store pesticides properly, in accordance with federal, state and local pesticide laws and regulations.
Dispose of empty pesticide containers promptly, safely, and according to the label.
Know the proper procedures for controlling, containing, and cleaning up accidental pesticide spills.
Know the symptoms of pesticide poisoning.
Seek medical attention immediately if poisoning is suspected. Take the pesticide label to the physician.
Know first aid procedures for pesticide poisoning and keep a first aid kit available.

For more information, see:

Marer, P., M. Flint, & M. Stimman. 1988. The safe and effective use of pesticides. University of California Publication 3324.

Managing Pesticide Resistance

By: Frank B. Peairs

Resistance is a naturally existing characteristic that can be inherited, that increases a pest’s ability to withstand the effects of the pesticide. Pesticide resistance is a growing problem. Nearly 450 species of insects and mites have developed resistance to one or more insecticides, including carbamates and organophosphates. More than 55 resistant weed species have been reported in the United States. Many systemic and some contact fungicides are prone to resistance because they attack fungi with a specific mode of action. Among the fungicides considered candidates for resistance are: bensimidaoles (Benlate, Tersan, Topsin M), phenylamides (Ridomil), dicarboximides (Rovral, Ronilan), and sterol inhibitors (Rubigan Bayleton, Tilt).

Rotate the mode of action of pesticides used in the field.
Use pesticides only when necessary.
Scout for resistance.
Utilize integrated pest management.