ED-STEEP: Education Solutions to Environmental
and Economic Problems
Pesticide Fact Sheet
Pests are organisms that are in the wrong place at the wrong
time. They interfere with humans because they compete for
crops or stored food, can cause or vector diseases, and cause
damage to buildings. Pesticides are designed to kill or deter
pests from causing problems
Types of Pesticides – by Target Organism
Pesticide
Target Organism
Herbicide
Fungicide
Insecticide
Acaricide
Nematicide
Avicide
Rodenticide
Bactericide
“weeds”
fungi
insects
mites
nematodes
birds
rodents/mammals
bacteria
Types of Pesticides – by Chemical Group
Kinds of Pesticides
 Inorganic compounds (mostly used as fungicides)
o Copper compounds
o Arsenicals
o Mercurials
 Naturally-occurring organic compounds
o Pyrethrins (from Chrysanthemums spp.)
o Rotenone (from Derris spp.)
o Nicotine (from Nicotinus spp.)
 Synthetic organic compounds
o Organochlorines or chlorinated hydrocarbons
 DDT, dieldrin, chlordane, lindane (insecticides)
 2,4-D, 2,4,5,-T (phenoxy herbicides)
o Carbamates
 Aldicarb, carbofuran (insecticides)
o Organophosphates
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 Fenitrotion, phosphamidon, diazinon (insecticides)
 Glyphosate (herbicide)
o Triazines
 Atrizine, metrabuzin (herbicides)
o Amides
 Alachlor (herbicide)
o Thiocarbamates
 Butylate (herbicide)
o Dinitroaniline
 Trifluralin (herbicide)
Biological pesticides
o Bacteria
o Fungi
o Protozoa
o Viruses
Insecticides that Affect the Nervous System
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Pyrethroids
o synthetic chemicals similar to pyrethrins found naturally in flower heads of certain
Composites (e.g., chrysanthemums)
o bind to sodium-channel proteins in nerve fibers, preventing them from “closing” and
causing continuous nerve stimulation
Carbamates
o bind to acetylcholinesterase in nerve synapses, causing continuous nerve stimulation.
Organophosphates
o bind to acetylcholinesterase (neurotransmitter) in nerve synapses, causing continuous
nerve stimulation.
Avermectins (and other macrolactones)
o derived from a fungus
o bind to gamma amino butyric acid (GABA)-gated chloride channels in nerve fibers,
causing continuous nerve stimulation.
Chloronicotinyls
o mimics the action of the neurotransmitter, acetylcholine, causing excessive nerve
stimulation
o more effective against insect nervous systems than mammalians systems
Phynylpyrazoles
o affect GABA-gated chloride channels
Insecticides that Affect Energy Production
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Amidinohydrazone (hydramethylnon)
o Binds to cytochrome proteins in the electron transport system in mitochondria,
blocking the production of ATP
Sulphonamides (sulfluramid)
o Converted into toxic metabolites by enzymes in the body
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Inorganic Fumigants (sulfluryl fluoride)
o Binds to cytochrome proteins in the electron transport system in mitochondria,
blocking the production of ATP
o Used mainly for killing termites
Insecticides that Affect Endocrine Systems
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Juvenile Hormone Analogs and Mimics (Hydroprene, Methoprene, Fenoxycarb,
Pyriproxyfen)
o Insect growth regulators (IGRs)
o Specific for insects
o Mimic insect juvenile hormone, causing the insect to remain in the juvenile stage
o Causes of slow death by inhibiting development
Insecticides that Affect Chitin Production
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Benzoylphenyl Urea (Diflubenzuron, Lufenuron, Hemaflumuron)
o Chitin synthesis inhibitors (CSIs); chitin is a major part of an insect’s exoskeleton
o Prevents insects from molting
Insecticides that Affect Water Balance
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Inorganics (borates, silica aerogels, diatomaceous earth)
o Silica aerogels and diatomaceous earth absorb oils and protective waxes on the
insect’s cuticle, causing rapid water loss
o Mode of action of borates not known
Herbicides that Affect Plant Growth (growth regulators)
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phenoxy acetic acids (2,4-D, MCPA)
benzoic acids (Dicamba)
pyridines (Clopyralid, Picloram, Triclopyr)
probably act at multiple sites in a plant to disrupt hormone balance and protein synthesis,
causing several plant growth abnormalities (stem twisting, callus tissue formation, leaf
rolling and other deformations, stalk bending)
selectively kill broadleaf weeds, but can affect grasses
can move in both the xylem and the phloem
uptake is primarily through the foliage but root uptake is possible
Herbicides that Inhibit Amino Acid Synthesis
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sulfonylureas (Chlorimuron, Chlorsulfuron, Primisulfuron, Thifensulfuron, Triasulfuron,
Nicosulfuron, Metsulfuron, Tribenuron)
imidazolinones (Imazamathabenz, Imazaquin, Imazethapyr)
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sulfonamide (DE-498)
amino acid derivatives (Glyposate)
sulfonylurea, imidazolinone, and sulfonamide herbicides prevent the production of three
amino acids by inhibiting the enzyme, acetolactate synthase.
amino acid derivative herbicides inhibit the production of three essential aromatic amino
acids by inhibiting the enzyme, 5-enolpyruvyl-shikimate-3 phosphate synthase
cause stunting, discoloration, slow growth, and plant death
sulfonylurea, imidazolinone, and sulfonamide families can move in both the xylem and
phloem
amino acid derivative herbicides are nonselective, move into the plant through foliage, and
are transported through the phloem
Herbicides that Inhibit Lipid Synthesis
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Aryloxyphenoxypropionates (Diclofop, Fluazifop, Fenoxaprop, Quizalofop)
Cyclohexanediones (Sethoxydim, Clethodim)
prevent the formation of fatty acids by inhibiting the enzyme, acetyl-CoA carboxylase,
needed plant lipid formation
Causes discoloration and abnormal growth of leaves,
Taken up by the foliage and move in the phloem to areas of new growth
Herbicides that Inhibit Seedling Growth
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Dinitroanilines (benefin, ethalfluralin, pendimethalin, trifluralin)
o root inhibitors
Acetanilides (alachlor, acetochlor, metolachlor, propachlor)
o shoot inhibitors
Thiocarbamates (EPTC, butylate, triallate)
o shoot inhibitors
Root inhibitors interfere with tubulin protein production during cell division
Root inhibitors cause stunting of plants, failure of plant emergence, thick lateral roots,
deformed hypocotyls
Shoot inhibitors probably have multiple sites of action
Shoot inhibitors cause stunting of shoots, failure of plant emergence, deformed leaves
Applied to the soil and only effective against seedlings
Move through the xylem to areas of new growth
Herbicides that Inhibit Photosynthesis
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Triazines (ametryn, atrazine, cyanazine, simazine, metribuzin, hexazinone)
Phenylureas (linuron, tebuthiuron)
Uracils (terbacil)
Benzothiadiazoles (bentazon)
Nitriles (bromoxynil)
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shut down photosynthesis by binding to D-1 quinone-binding proteins of photosynthetic
electron transport within the plant’s chloroplast
cause a slow starvation of the plant, yellowing and death of leaf tissue
triazines, phenylureas, and uracils are taken up into the plant via the roots or foliage and
move in the xylem to plant leaves
The nitrile and benzothiadiazole herbicide families are not mobile in plants and are not taken
up from the soil. They are “contact” herbicides that must cover the plant’s foliage to work
Herbicides that Disrupt Cell Membranes
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Diphenylether (acifluorfen, lactofen, fomesafen)
Bipyridylium (paraquat, difenzoquat)
When exposed to sunlight, they form oxygen compounds (e.g., hydrogen peroxide) that
destroy plant tissue by rupturing plant cell membranes
Cause plant tissue necrosis
Because they are contact herbicides, they have very little activity in the soil
Bipyridyliums are activated by photosystem I (PSI)
Diphenylether inhibit protoporphyrinogen oxidase (Protox)
Herbicides that Inhibit Plant Pigmentation
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Isoxazolidinones (clomazone)
o Turn plants white by preventing the formation of photosynthetic pigments
o Site of action unknown
Pyridazinones (norflurazon)
o Turn plants white by preventing the formation of photosynthetic pigments
o Phytoene and phytofluene enzymes of the terpenoid pathway
Fungicides
Fungicides affect fungi in several ways:
 Inhibit the formation of cell walls
 Affect the permeability of the cell wall, causing a loss of cytoplasm
 May interfere with the function of essential metals in the cell (e.g., bind with metalcontaining enzymes involved in ATP synthesis)
 Inhibit respiration
 Inhibit nuclear division
 Break dormancy of spores
 Inhibit germination of spores
References
Valles, S.M. and P.G. Koehler. School IPM. Integrated Pest Management in Schools
Weed Research and Information Center, University of California Cooperative Extension