Pest control professionals and homeowners
are seeking effective options that are safer for people and the environment than some conventional
synthetic pesticides. There is also rising interest in organic gardening,
which relies on natural pesticides. Natural or biological pesticides, also called
biopesticides, can be used by themselves or in combination with conventional pesticide
programs as valuable rotation options, thus delaying or preventing onset of resistance
caused by repeated use of the same chemical controls. I’m Dr. DeBusk and in this video I’ll
describe natural products for use against insects. There is a general lack of knowledge about
natural or biological pesticides, including commercial availability and effective use. All pesticides, whether natural or synthetic,
carry inherent risks and require safe and responsible use by the applicator. Ideally, natural insecticides and fungicides
should reduce insect or disease problems, be specific to the pest, break down quickly,
have low mammalian toxicity, and have minimal impact on the environment. General traits of natural products include
the following. Most natural products degrade rapidly in sunlight,
air, or moisture, or when exposed to insect detoxification enzymes if ingested. Rapid breakdown means these products do not
persist long in the environment, which reduces risk to nontarget organisms. However, it also means precise timing and
more frequent applications may be necessary. Some natural products, such as soaps and oils,
kill insects upon contact. Ingestion of others (for example, Bacillus
thuringiensis and spinosad) causes pests to quickly stop feeding, although death may not
occur until hours or days later. Most of the natural products discussed here
have low to moderate acute mammalian toxicity. Growers should also be aware of potential
disadvantages of natural products. Vegetables and ornamental plants can be damaged
by insecticidal soaps, horticultural oils, plant oils, and sulfur, especially at higher
rates or application frequency. This is called phytotoxicity as seen in these
photos. The effects are likely more pronounced for
stressed plants and in hot, sunny conditions. Natural products, especially OMRI-approved
versions, are sometimes more expensive than conventional pesticides, and some are hard
to obtain. Many pesticides registered by the EPA can
be purchased online but are not registered for legal sale in certain states. Many natural ingredients used to make pesticides
are exempt from the rigorous review process usually required by the EPA. Data on pest control efficacy, long-term health
effects, and tolerances for residues on food crops have not been established. Citrus oils, which are extracted from oranges
and other citrus fruit peels, can be refined to make the compounds d-limonene and linalool,
which are used as insecticides. Limonene and linalool are contact poisons
(nerve toxins). A synergist (a substance that works with a
product to increase its effectiveness) such as piperonyl butoxide (PBO) can be used. The way it works is that PBO blocks insect
detoxification enzymes (the blue circles), so the insecticide (the yellow diamonds) can
bind to the sodium channels. Both limonene and linalool evaporate readily
from treated surfaces and have no residual activity. They have been registered for use against
fleas, aphids, and mites, but they also kill fire ants, several types of flies, paper wasps,
and house crickets. Commercial products (usually containing d-limonene)
are available as liquids, aerosols, shampoos, and dips for pets. Contact with skin or eyes can be irritating
to some animals, but symptoms are usually temporary. Use with caution to minimize phytotoxicity
to new or sensitive plants. Neem oil is extracted from seeds of the neem
tree which is native to India. Pure neem oil, often called cold pressed neem
oil, contains several insecticidal and fungicidal chemical compounds. For the most common type of product, an extraction
process removes the primary insecticide, azadirachtin, and related compounds, referred to as neem
oil. They function like insecticidal soap and other
horticultural oils, requiring direct contact and thorough coverage to effectively smother
and kill pests. Similarly, they work best against soft-bodied
pests, such as aphids, whiteflies, spider mites, and mealybug and scale nymphs. Certain neem oil products are also labeled
for prevention of several foliar plant diseases include powdery mildew and some rusts. Another type of neem product makes use of
concentrated azadirachtin after it is separated from the neem oil. Azadirachtin is used to control a wide range
of pests, including caterpillars, sawflies, flea beetles, weevils, aphids, and leafhoppers. Azadirachtin can control several insect groups
by acting as a feeding deterrent, deterrent to egg-laying, repellent, direct toxin, or
insect growth regulator. These products work well against the immature
stages of chewing insects. After ingesting a treated plant, the juvenile
insect may be unable to molt to its next life stage and die within a few days. Azadirachtin has some systemic activity when
applied to roots and is weakly systemic in leaves, allowing it to control leafminers. Some products may be labeled for use as a
soil drench for pests such as fungus gnats. Many products containing highly concentrated
plant oils besides citrus and neem are commercially available, and are often referred to as essential
oils. Many of these oils have bioactive components,
providing toxicity to pests beyond simply smothering them. They may be able to affect larger insects,
whereas other horticultural oils are more limited to small and soft-bodied insects. However, there is a lack of consistency among
products, as well as large natural variation among essential oil compositions. Since the oils may work well against certain
insects but not others, treatments should be observed for efficacy. The most common oils used in these products
are sesame, garlic, canola, and soybean. Some herbal extracts include oils from thyme,
rosemary, peppermint, cinnamon, and clove. Others—such as cedar, lavender, eucalyptus,
pennyroyal, and citronella—are commonly used as flea and mosquito repellents on pets
and humans, but their effectiveness varies depending on the plant compounds, concentration,
application method, and product formulation used. Horticultural oils (often called hort oils,
spray oils, or summer/dormant oils) are highly refined, lightweight oils that are most often
derived from petroleum. The oil is mixed with water and sprayed as
a fine mist onto plant foliage and bark. When used correctly, horticultural oils can
help manage many piercing-sucking insects and mites. They work best against small, soft-bodied
insects such as aphids, whitefly nymphs, mealybug nymphs, and scale insect nymphs. When sprayed onto insects, plant and petroleum
oils can block the insects’ breathing holes (spiracles) and cause them to suffocate. Oils can prevent gas exchange through egg
membranes, so eggs are also targets of control with oils. The fatty acids in plant oils may disrupt
cell membranes and interfere with insect or mite metabolism. Some oils may also have repellent or anti-feeding
properties, which can help reduce colonization by more mobile insects. Insecticidal soaps, containing potassium salts
of fatty acids, are made by adding potassium hydroxide to salts of fatty acids, which are
found in fats and oils of animals, such as lard and fish oil, and plants such as cottonseed,
olive, palm, or coconut. The resulting soap products are useful against
soft-bodied pests such as aphids, soft scales, psyllids, whiteflies, mealybugs, thrips, and
spider mites. While the mode of action is not fully understood,
insecticidal soaps are thought to work by penetrating and disrupting the insects’
cell membranes, removing protective waxes from the outer cuticle and causing dehydration,
and blocking breathing holes to cause suffocation. Like oils, soap sprays must contact the insect
directly to be effective, and residues that remain on plants after drying have no insecticidal
effect. Plants with hairy leaves or plants that are
suffering from drought stress may be more sensitive to soaps. In general, while other soaps found in the
home can kill insects, they are often not as effective and pose greater risk of injury
to the plant. Pyrethrins are highly concentrated compounds
extracted from the daisy-like flower of Tanacetum cinerariifolium, commercially grown in Kenya. When the flower is ground into a powder, the
product is called a pyrethrum. Pyrethrins may be used against a broad range
of pests, such as ants, roaches, fleas, flies, ticks, and garden pests. They are available in dusts, sprays, and aerosol
“bombs,” and are often mixed with synthetic pesticides or other natural products. Do not confuse the similar-sounding pyrethroids
(e.g., bifenthrin, cyfluthrin, permethrin, and others) with pyrethrins. Pyrethroids are relatively long-lasting synthetic
insecticides that have the same mode of action as pyrethrins but may pose greater risks to
predator and parasitoid insects. Many insect groups are susceptible to low
concentrations of pyrethrins. The toxins act rapidly on contact, quickly
reaching the insect’s nervous system to cause knockdown or paralysis; however, insects
may metabolize them and recover. To prevent recovery, a synergist such as PBO
or MGK 264 is often included in the mixture. Pyrethrins break down quickly, have short
residual activity, and have low mammalian toxicity, making them among the safest insecticides
in use. Pyrethrins are toxic to fish, so use caution
when applying these products near water sources. Diatomaceous earth (DE) is mined from the
fossilized silica shell remains of diatoms (single-celled aquatic algae). The particles have sharp edges that abrade
and absorb the water-protecting oils and waxes from an insect’s outer body, causing it
to dehydrate and eventually die. Products are usually designed for use against
indoor and structural pests, such as ants, fleas, bed bugs, and cockroaches. Evaluations show that it is not practical
for outdoor insects, and mollusks are generally not killed or repelled from feeding. One problem is that it must remain completely
dry to be effective. This makes it very difficult to use in Florida’s
humid climate. Insecticidal DE has very low mammalian toxicity,
but as a fine dust it can pose a mild inhalation hazard, so the use of a dust mask is suggested. This naturally occurring clay mineral (aluminum
silicate) is finely processed so that it can be mixed with water and sprayed evenly onto
leaves, stems, and fruit. It leaves a powdery white film that helps
prevent both insect damage and sun scorch from heat and intense sunlight. Kaolin clay can also help deter insects as
a mildly irritating physical barrier by repelling them from feeding and laying eggs, or by making
plants difficult to recognize. While kaolin is not toxic to humans, heavy
use may be harmful to beneficial insects that also need to live on the plants. Complete coverage of the plant and reapplication
after heavy rains are necessary for this treatment to be effective. Sulfur is thought to be the oldest known pesticide
in current use and dates back to the Roman era. It can be used as a dust, fumigant, wettable
powder, paste, or liquid. Sulfur is used primarily for disease control,
but it can also help with control of mites, psyllids, and thrips. However, natural enemies such as predatory
mites and parasitoids are susceptible as well. Most pesticidal sulfur is labeled for vegetables
and fruit crops, but some crops, such as cucurbits and raspberries, may not appear on a label
because they are easily damaged by sulfur. Sulfur is considered nontoxic to mammals,
but it may irritate skin or eyes. Sulfur has the potential to damage plants
in dry, hot weather (when temperatures are near or above 90°F one to two days after
application) and is incompatible with some other pesticides. One of the more familiar and commonly used
microbial products is spinosad, which is derived from a species of soil bacteria. Much like Bt, this bacterium produces an insecticidal
toxin during fermentation. Spinosad is relatively broad-spectrum and
controls a wider range of pests than other microbials, including caterpillars, leafminers,
flies, thrips, beetles, and spider mites. Spinosad attacks the nervous systems of insects
that come into contact with or ingest it. Feeding stops within minutes and death occurs
within two days. When used correctly, it has low to moderate
toxicity to beneficial organisms and very low toxicity to mammals and wildlife. It is highly toxic to bees when the spray
is wet, but dry residues have minimal effect. Therefore, applications should be made during
the early morning or late evening, or at night when pollinators are not actively foraging. Natural pesticides are generally less toxic
to nontarget organisms and the environment when used correctly, can be effective tools
for plant protection. These products are most effective when used
in an integrated pest management program along with sanitation, proper cultural practices,
mechanical control tactics, use of resistant plant varieties, and biological control. See the Organic Materials Review Institute
(OMRI) website for products that are acceptable in organic plant production.