Least Toxic and Organic Pesticides for Gardeners

Least toxic pesticides that are labeled as natural or organic are not necessarily harmless to humans or the environment. Many are quite safe to use. Some have hazards associated with them. Always read the label very carefully and follow label directions. Wear protective clothing whenever you use any pesticide. Even those products that are nontoxic can be irritating to skin, eyes and mucous membranes.

These descriptions are not recommendations for use. For current OSU recommendations, consult the most recent Pacific Northwest Plant Disease Management, Insect Management and Weed Management Handbooks.

The products listed for each active pesticide are examples only. The lists do not include all products that may be currently available.

Insecticides

Botanical insecticides

  • Rotenone
    • Source: derived from the roots of several tropical legumes
    • Mode of action: broad spectrum contact and stomach poison, inhibits cell respiration, causes cessation of feeding and death
    • Uses: broad spectrum, particularly effective against leaf-feeding beetles and certain caterpillars Toxicity: most formulations have low mammalian toxicity, emulsifiable concentrate is highly toxic (and restricted use), extremely toxic to fish, keep away from water
    • Notes: often found in combination with pyrethrins for general pest control, degrades quickly under warm, sunny conditions
  • Pyrethrum and pyrethrins
    • Source: derived from Chrysanthemum cinerariaefolium, pyrethrum is crude flower dust itself, pyrethrins are insecticidal compounds that occur naturally in the crude material
    • Mode of action: contact poison, causes an immediate "knockdown" paralysis in insects
    • Uses: often formulated with other botanicals for general garden use, on pets and livestock for flea, fly and mosquito control, against indoor insect pests
    • Toxicity: low mammalian toxicity, toxic to bees and aquatic life, can cause an allergic reaction in humans and cats
    • Notes: degrades rapidly in sunlight, often formulated with synergist, PBO, which is not allowed in certified organic programs PBO= It is a synthetic synergist that gives the basic insecticide more killing power by blocking the animal’s power to detox the primary poison.
  • Neem (azadirachtin)
    • Source: neem tree (Azadirachta indica), grows in arid tropical and subtropical regions
    • Mode of action: contains 25 active compounds that act as feeding deterrents, repellants, growth regulators, toxins and sterilants, has both contact and systemic action in plants, blocks hormones that control metamorphosis
    • Uses: broad spectrum against many garden and household pests, may be useful against hard-to-control leaf-feeders like cucumber beetle and adult root weevil, may require repeat applications
    • Toxicity: low to very low mammalian toxicity, most beneficials unaffected because neem must be directly ingested
    • Products: Bioneem, Neemix, Neem Away
  • Ryania (ryanodine)
    • Source: woody stems of Ryania speciosa, a South American shrub
    • Mode of action: slow-acting stomach poison, insect stops feeding soon after ingesting
    • Uses: effective against some caterpillars, used mostly for codling moth, Oriental fruit moth, and corn earworm
    • Toxicity: low to moderate mammalian toxicity
    • Products: Ryan 50
    • Notes: most effective in hot weather, sometimes mixed with diatomaceous earth, persists for approximately 1 week
  • Sabadilla
    • Source: ripe seeds of Schoenocaulon officinale, a tropical lily from Central and South America
    • Mode of action: broad spectrum contact poison, some activity as a stomach poison
    • Uses: Effective against some true bugs, i.e. stink bugs, squash bugs, also cucumber beetles, leafhoppers, loopers
    • Toxicity: Low mammalian toxicity, toxic to bees
    • Products: Red Devil Dust, Natural Guard
    • Notes: degrades rapidly in air and sunlight, highly toxic to honeybees, do not use on blooming plants or when honeybees are active
  • Nicotine
    • Source: simple alkaloid derived from tobacco, Nicotiana tabacum
    • Mode of action: fast-acting nerve toxin, contact poison and fumigant activity Uses: effective against sucking pests such as aphids, thrips, mites
    • Toxicity: High mammalian toxicity!
    • Products: Black Leaf 40
    • Notes: degrades in 24 hours
  • Citrus oil (limonene)
    • Source: citrus peels and citrus peel oil
    • Mode of action: contact poison
    • Uses: combine with soap against fleas, ticks, mites, and aphids Toxicity: low mammalian toxicity, mild irritant to skin, nose, eyes Products: Orange Guard, Bug Ban, Duel, Sharpshooter
    • Notes: evaporates quickly after application, also used in solvents and cleaning products

Inorganic insecticides

  • Sulfur
    • Notes: abrasive to metal, use plastic spray equipment, can burn plants at temperatures above 90 degrees F., no not use within one month of oil spray, also acts as a fungicide
    • Toxicity: very low mammalian toxicity, can be irritating to eyes, ears and nose
    • Uses: most effective as a miticide, also useful against aphids and thrips, on fruits, vegetables, flowers, ornamentals
    • Mode of action: disrupts mite and insect metabolism
    • Source: elemental sulfur, naturally occurring mineral
  • Kaolin clay
    • Source: naturally occurring mineral
    • Mode of action: particle film acts as a physical barrier between pest and plant, also irritates and repels insect feeding and egg-laying
    • Uses: used primarily on orchard crops and berries as a broad spectrum crop protectant, used against codling moth, apple maggot and spider mite
    • Toxicity: no mammalian toxicity, also used as a food additive Products: Surround
    • Notes: full coverage important, repeat applications necessary, also protects fruit against sunburn and heat stress
  • Iron phosphate
    • Source: naturally occurring mineral
    • Mode of action: stomach poison for slugs and snails Uses: against slugs and snails throughout the garden and landscape
    • Toxicity: very low mammalian toxicity (used as nutritional supplement), safe for wildlife, including earthworms and ground beetles
    • Products: Sluggo, Escar-Go, WorryFree
    • Notes: applied as a pellet whose inert ingredients serve as bait for slugs and snails, remains effective even in rain
  • Boric acid
    • Source: naturally occurring mineral
    • Mode of action: stomach poison, also desiccation due to abrasion of exoskeleton, causes death in 3-10 days
    • Uses: used indoors against cockroaches, ants, silverfish, termites, fleas, some weevils and beetles
    • Toxicity: low mammalian toxicity, may act as an irritant by inhalation Products: Roach Kill, Flea Stoppers, Drax Ant Bait, Boracare
    • Notes: long residual life if kept dry, use away from continual human contact

Insecticidal dusts

  • Diatomaceous earth
    • Source: mined from fossilized shell remains of diatoms
    • Mode of action: absorbs waxy cuticle layer on surface of insect skins, causes insect to desiccate, also abrades and ruptures cuticle
    • Uses: dust on plants as a nonselective insecticide, use as a thick border for ants, slugs, snails (1/4" deep, 2" wide) and indoors for crawling insects
    • Toxicity: very low mammalian toxicity, irritating to eyes, lungs
    • Products: DE, Dia-Secticide, Insect Stop
    • Notes: rain and irrigation water substantially decreases effectiveness, keep as dry as possible, use goggles and dust mask when applying, use only natural grade, not chemically treated swimming pool grade, sometimes formulated with selected baits and/or pyrethrins

Biological Insecticides

  • Bt (Bacillus thuringiensis)
    • Source: naturally occurring bacterium produced en masse in the lab
    • Mode of action: bacterial stomach poison that must be ingested by insect to be toxic, initial poisoning causes cessation of eating, insect dies in a few days
    • Uses: Bt kurstaki used against plant-eating caterpillars, Bt israelensis used against mosquitoes and fungus gnats, Bt san diego used against elm leaf beetle and Colorado potato beetle
    • Toxicity: mammalian toxicity varies from low to very low toxicity depending on product
    • Products: Caterpillar Killer, Dipel, Gnatrol, Bactimos, Potato Shield
    • Notes: biodegrades quickly in sunlight, spray late in day or on a cloudy day, need full plant coverage, Bt kurstaki works best when caterpillars are still small
  • Beauveria bassiana
    • Source: common soilborne fungus
    • Mode of action: fungus infects through contact with insect, does not need to be ingested, kills in 3-7 days
    • Uses: used against a wide range of foliar-feeding insects including whiteflies, aphids, thrips, mealybugs, beetles, weevils, mites and caterpillars, indoor and outdoors throughout garden and landscape
    • Toxicity: nontoxic to humans and wildlife, may be harmful to bees, avoid spraying when bees are present
    • Products: Naturalis, Mycotrol, Botanigard
    • Notes: thorough coverage needed, repeat applications may be necessary, do not apply fungicides within 24 hours, works best under moist, humid conditions
  • Spinosad
    • Source: fermentation product of soil-dwelling actinomycete, Saccharopolyspora spinosa
    • Mode of action: kills insect mainly by ingestion, some contact, kills by excitation of insect nervous system, insects die 1-2 days after ingestion
    • Uses: effective against a broad range of insects including fruit flies, caterpillars, leafminers, thrips, sawflies, leaf beetles
    • Toxicity: low mammalian toxicity, conserves most beneficial insects, use care on blooming plants, can affect bees
    • Products: Garden Insect Spray, Conserve, Entrust, Bulls-Eye
    • Notes: useful against insects that have been traditionally hard to control without commercial pesticides such as fruit flies, leafminers, and corn earworm
  • Entomopathogenic nematodes
    • Source: naturally occurring, reared en masse in the laboratory
    • Mode of action: juvenile stage of nematode infects through insect body openings, multiplies, kills host by infecting with symbiotic bacteria
    • Uses: against soil-dwelling larvae and pupae of a variety of insects, most effective at or near soil surface, useful in western Oregon in late summer against root weevil larvae
    • Toxicity: very low mammalian toxicity
    • Notes: will not survive dry conditions - soil should be moist, soil temperature must be above 55 degrees F. If conditions are favorable, nematodes will complete their life cycle in host, then new juveniles will migrate out in search of a new host. Two species, Steinernema carpocapsae and Heterorhabditis sp., are used, depending on host preference.

Miscellaneous

  • Insecticidal soaps
    • Source: potassium salts of fatty acids
    • Mode of action: contact insecticide that includes physical disruption of insect cuticle, smothers and desiccates insects
    • Uses: against soft-bodied insects such as aphids, thrips, whitefly, mites and other slow-moving, flightless insects Toxicity: low mammalian toxicity
    • Products: many
    • Notes: requires excellent coverage, may require repeat applications, biodegrades rapidly, only effective until it dries, may kill immature beneficials, use according to label directions - can be phytotoxic
  • Horticultural oils
    • Source: may be petroleum based, vegetable based (mint, rosemary), fish
    • Mode of action: smothers insect and mite eggs, blocks breathing apparatus of immature and adult insects and mites
    • Uses: against broad spectrum of insects and mites, especially aphids, mites, caterpillars and other soft-bodied insects
    • Toxicity: low to very low mammalian toxicity, may irritate eyes and skin
    • Products: many
    • Notes: degrades rapidly, dormant oils are generally heavier and used on woody plants during the dormant season, lighter oils can be used on most plants during the growing season, avoid spraying in the heat of the day, do not use on drought-stressed plants
  • Garlic
    • Source: garlic bulbs
    • Mode of action: primarily a repellant
    • Uses: as a preventative treatment against leaf-feeding and sucking insects, also has fungicidal properties Toxicity: non-toxic
    • Products: Garlic Barrier
    • Notes: repeat sprays on a weekly basis, odorless shortly after application, use oil as a sticker-spreader and additional insecticide, nonselective
  • Hot pepper wax (capsaicin)
    • Source: hot peppers
    • Mode of action: contact and repellent, metabolic stimulant for soft- bodied insects
    • Uses: used as a general purpose insecticide/repellant for soft- bodied insects on wide variety of garden plants
    • Toxicity: nontoxic
    • Notes: formulated with paraffin wax, watch for leaf damage, requires repeat applications, nonselective

Fungicides

  • Copper (basic copper sulfate, copper hydroxide, tribasic copper sulfate)
    • Uses: as a broad spectrum protectant fungicide and bactericide in fruits, vegetables and ornamentals against mildew, brown rot, leaf spots, blights, scab, anthracnose and rusts, primarily used with spreader/sticker during dormant season
    • Mode of action: kills spores by disrupting function of enzymes
    • Products: Microcop and others
    • Toxicity: highly toxic to humans through ingestion and inhalation, and eyes, highly toxic to fish and other aquatic organisms Notes: discoloration of flowers and foliage can occur
  • Lime sulfur (calcium polysulfide)
    • Uses: as a broad spectrum protectant fungicide and insecticide against peach leaf curl, brown rot, leaf spot, powdery mildew, scab, anthracnose, and overwintering mites, scales and aphids, use as dormant or delayed dormant spray on fruit trees and many ornamentals
    • Mode of action: contact poison
    • Products: Polysul
    • Toxicity: low mammalian toxicity, significant irritant to skin, eyes, lungs
    • Notes: do not mix with other pesticides, can mix with oil, very alkaline, will react with acids to produce toxic gas
  • Sulfur
    • Uses: broad-spectrum fungicide/miticide used on fruits, vegetables, and ornamentals against rusts, leaf spots, powdery mildew, scab, mites
    • Mode of action: prevents germination of spores, contact poison
    • Products: Garden Fungicide
    • Toxicity: Low mammalian toxicity, toxic to fish, irritating to skin, eyes, nose and throat
    • Notes: do not use within two weeks of an oil spray, some plants sensitive to sulfur, check product label
  • Horticultural oil (petroleum based, mineral, fish, jojoba, mint)
    • Uses: as a protectant and sometimes eradicant against certain ectoparasitic fungi, especially powdery mildew, on wide variety of garden plants
    • Mode of action: physical disruption of fungi, interferes with attachment to host, destroys fungal cell walls Products: many (Sunspray Ultra-fine Oil, E-Rase, Fungastop, JMS Stylet etc.)
    • Toxicity: very low
    • Notes: use superior or summer weight oils during growing season, do not use on drought-stressed plants, need excellent coverage for adequate control, helps control viruses by controlling aphid vectors
  • Potassium bicarbonate
    • Uses: as a protectant fungicide used against powdery mildew in a wide variety of vegetable crops (particularly cucurbits) and ornamental plants
    • Mode of action: bicarbonate ion inhibits growth in some fungi and bacteria
    • Products: Kaligreen, Remedy, FirstStep
    • Toxicity: very low
    • Notes: does not protect against black spot on roses, direct contact with fungus necessary, including oil as a sticker/spreader greatly increases effectiveness, use every 7-10 days for season-long protection, will provide some K fertilization
  • Neem oil (azadirachtin)
    • Uses: preventative broad spectrum fungicide on ornamentals, vegetables, fruits and nuts, and landscape plants both indoors and out for mildew, scab, rusts, and black spot
    • Mode of action: prevents adhesion of fungal spores to plant surface
    • Products: Shield-All II, Garden Safe Fungicide 3, Bioneem irritating to skin
    • Toxicity: low to very low
    • Notes: thorough coverage necessary, do not apply to drought-stressed plants, also acts as a broad spectrum insecticide/miticide
  • Antitranspirants
    • Uses: to prevent fungal diseases such as powdery mildew, gray mold, and blackspot on a variety of garden and landscape plants
    • Mode of action: waxes, silicones and other plastic coatings increase thickness and integrity of leaf cuticle, results in significant physical barrier to fungal penetration of leaf, also repels water needed for fungal spore germination Products: Wilt Pruf, Vapor Gard
    • Toxicity: low toxicity, biodegradable
    • Notes: reapply regularly to protect new growth

Biological

  • Gliocladium virens GL-21
    • Uses: naturally occurring soil fungus used to suppress soil-borne plant pathogens such as Pythium, Rhizoctonia, Sclerotinia and Fusarium that cause damping-off and root rots in greenhouse ornamentals and food crops
    • Mode of action: fungus parasitizes, competes with, and excludes plant pathogens
    • Products: Soil Gard
    • Toxicity: nontoxic, nonpathogenic, noninfective
    • Notes: can be used in soil or in soilless potting mixes
  • Streptomyces griseoviridis K61
    • Uses: soil bacterium that prevents certain plant pathogenic fungi from infecting plants, helps prevent seed rot, root rot, damping off and wilt, used on greenhouse ornamentals, herbs and vegetables
    • Mode of action: several modes of action including earlier colonization of plant roots and production of chemicals that may actively attack harmful fungi
    • Products: Mycostop
    • Toxicity: nontoxic, may cause irritation to eyes, skin and lungs
    • Notes: use at seeding or transplanting, do not mix with pesticides or fertilizers

Herbicides

Note: (Because a product is listed here does not necessarily mean that it has scientifically been proven to be effective through research based credible experimentation. Vinegar products and corn gluten fall into the “not proven to be effective” category).

  • Vinegar (acetic acid)
    • Uses: 5-20% concentration of acetic acid will kill selected annual weeds and tops of certain perennial weeds
    • Mode of action: contact, acetic acid damages plant cells, plant dries out
    • Products: Burn-Out
    • Toxicity: non-toxic, biodegradable, acetic acid concentrations of this level can cause dermatitis and serious eye damage if splashed in eyes
    • Notes: spray young actively growing weeds in spring, weeds should dry out in 6-24 hours, will not kill underground portion of plant, homemade vinegar solutions not registered as pesticides - do not recommend
  • Herbicidal soap (potassium salts of fatty acids)
    • Uses: used to control annual weeds, aerial portions of perennial weeds, moss, and algae Mode of action: soap penetrates waxy cuticle, plant dries out
    • Products: Superfast Weed and Grass Killer, Weed-Aside
    • Toxicity: very low mammalian toxicity, biodegradable
    • Notes: non-selective, keep off of desirable vegetation, apply in spring when plants are small and actively growing, less effective on grasses and older weeds
  • Corn gluten meal
    • Uses: prevents growth of certain weed seedlings, used primarily in turf plantings, but can be used anywhere Mode of action: inhibits root formation of germinating seeds
    • Products: WOW!, Bio-Weed, Weed Prevention Plus, WeedBan
    • Toxicity: nontoxic, biodegradable
    • Notes: time application to coincide with seed germination, also effective as a fertilizer due to 10% nitrogen content

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