Following is a brief description of some least toxic botanical and mineral pesticides as well as biological controls available for managing insect pests, including insecticidal soaps, pyrethrum/pyrethrins/pyrethroids, rotenone, ryania, sabadilla dust, nicotine sulfate, superior horticultural oil, ladybird beetles, lacewings, predatory mites, trichogramma wasps, and Bacillus thuringiensis (Bt).
These are broad-spectrum insecticides. Pyrethrum powders are made directly from the flowers of a species of chrysanthemum, and pyrethrins are the active compounds from the pyrethrum flower. Pyrethroids are synthesized pyrethrins. These materials disrupt the nervous system of insects and cause paralysis. They are fast-acting and often used for their "knock-down" effects to quickly reduce large insect pest populations. They are moderately toxic to humans and other mammals and break down quickly from sunlight, moisture, and oxygen, leaving no residues. They are often combined with rotenone and/or ryania to provide more effective and longer lasting results.
Rotenone is derived from the roots of several leguminous plants and is a broad-spectrum contact and stomach poison that affects insect nerve and muscle cells, causing the insects to stop feeding and die anywhere from a few hours to a few days after ingestion. It is most effective against leaf-eating caterpillars and beetles, can be applied as a spray or dust, and is available in a variety of strengths as well as in combination with pyrethrin and ryania. If rotenone is eaten by humans or other mammals it is broken down by the liver with no long term negative effects. It can be dangerous if large amounts are inhaled.
Caution: Rotenone is extremely toxic to fish! Keep out of water; special care should be taken near areas which contain fish populations.
Ryania is extracted from the stems of a woody South American plant and is a stomach poison that causes insects to stop feeding soon after ingestion. It is reported to be most effective when used in hot weather. Ryania is moderately toxic but considered to be relatively harmless to humans and other mammals.
Sabadilla is a broad spectrum insecticide that comes from the seeds of a lily indigenous to Central and South America. It affects the nerve cells of insects, causing paralysis and then death. It is primarily used for adult insects that are hard to control with other botanical insecticides. Although the dust is considered to be the least toxic of all registered botanical insecticides, the active alkaloids in its pure, extracted form are very toxic and can make a person sick if ingested or absorbed through the skin and mucous membranes. Sabadilla is highly toxic to honeybees and should only be used in the evening, after they have returned to their hives. It degrades rapidly in sunlight and air, leaving no harmful residues.
Nicotine sulafate is a contact poison derived from tobacco and is one of the most toxic botanical insecticides. It causes severe disruption and failure of the human nervous system, is easily absorbed through the eyes, skin, and mucous membranes, and is extremely fast-acting. Nicotine Sulfate should only be used as a last resort. Best results have been reported with diluted mixtures. It biodegrades rapidly with little residual effect.
Superior Horticultural Oil
Also called dormant oil, this is a highly refined mineral oil that kills insects and their eggs by suffocating them. It is applied in late winter or very early spring to kill scales, aphids, and other overwintering insects. It is also used in the fall to kill eggs.
Ladybug larvae and adults are predators of aphids, small worms, and other soft-bodied insects. Release at the rate of 7,000 per 5,000 square feet in the evening or early morning when they are calm and slow moving.
Lacewing larvae prey on aphids, immature scales, spider mite eggs and most other soft-bodied insects or eggs. It is the best all purpose biocontrol predator available. Release at the rate of 1,000 eggs per 200 square feet for aphid infestations and 1,000 eggs per 900 square feet as a preventive treatment. Three successive releases at 5-7 day intervals are recommended. For release into trees, small amounts can be placed in paper cups and stapled to the leaves or branches. The larvae feed on pests for 1-3 weeks until they become adults, which primarily eat nectar and honeydew. Adults will lay eggs to ensure a continued lacewing population.
Predatory mites are released to control the two-spotted spider mite and other pestiferous mite species. Predatory mites are most effective if they are released when no more than 10% of the infested plant's leaves have spider mites. Heavy infestations should first be treated with insecticidal soap followed by weekly releases of predators until under control. Release at the rate of 200 per 100 square feet.
Trichogramma wasps are tiny parasites (4 or 5 would fit on the head of a pin!) that lay their eggs into the eggs of over 200 species of moths and butterflies. The larvae then feed on the pest eggs. The best time to release them is in cool evenings and early mornings. A sequence of 3 releases at two week intervals is recommended.
Bacillus thuringiensis (Bt)
Bt is a bacterium used to control the larvae of moths, butterflies, mosquitos, and other insect pests. It is sprayed or dusted onto leaves and when target insects eat it they stop feeding, become paralyzed, and die. Different strains of Bt have been developed and each one is effective only for the specific pest or group of pests for which it is intended, including the larvae of spruce budworm, tent caterpillars, mosquitos, and many others.
Source: IPM Access - An Integrated Pest Management Online Service
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