Insect Management

Botanicals

Plants have evolved their own chemical defenses against insects. When extracted from plants, these chemicals are referred to collectively as 'botanicals.' Generally botanicals degrade more rapidly than most conventional pesticides, and so are considered relatively environmentally benign and less likely to kill beneficials than insecticides with longer residual activity. Because they generally degrade within a few days, and sometimes within a few hours, these insecticides must be applied more often, however. More frequent application, plus higher costs of production usually makes botanicals more expensive to use than synthetic insecticides. Although a 'natural' product, botanicals are not labelled for all crops and not all are allowed by organic certification standards. Toxicity to other organisms is variable, although as a group, they tend to be less toxic to mammals (with the exception of nicotine) than non-botanicals.

Pyrethrum

Pyrethrum is the dried flower of Chrysanthemum cinerariaefolium which grows chiefly in Kenya and Tanzania. Pyrethrins are insecticidal chemicals extracted from the pyrethrum flower. Pyrethrins are nerve poisons that cause immediate paralysis to most insects. Human allergic reactions are common, and cats are susceptible to pyrethrins.

Many insects eventually recover from pyrethrum paralysis so piperonyl butoxide (PBO) is added to most commercial products to increase toxicity. Both highly alkaline and highly acid conditions speed up degradation so pyrethrins should not be mixed with lime or soap solutions. Liquid formulations are stable in storage but powders may lose up to 20 percent of their effectiveness in one year. Pyrethrins break down very quickly in sunlight. Pyrethroids are synthetic insecticides, chemically similar to pyrethrins but more toxic and longer lasting. They are not allowed in certified organic programs.

Rotenone

Rotenone is extracted from the roots of several tropical legumes such as the Cube plant grown in Peru. Originally used as a fish poison by the Indians, it is highly toxic to fish and moderately toxic to humans. A broad spectrum poison mainly used to control leaf-eating beetles and caterpillars, rotenone breaks down quickly in sunlight or when mixed with soaps or lime.

Toxicity of Botanical Insecticides

*LD50 - Lethal dose that kills 50% of the organisms exposed to it in tests, expressed in mg chemical per kg of body weight.

**Not an insecticide but increases efficacy of insecticides such as pyrethrins, by making them more lethal.

Sabadilla

Sabadilla is an alkaloid derived from the seeds of a tropical American lily. It is most effective against true bugs such as harlequin bugs and squash bugs. Sabadilla degrades quickly. The purified form is highly toxic to mammals. The dust is moderately toxic to mammals, but is highly toxic to honey bees.

Ryania

Ryania is an alkaloid derived from the stems of a South American shrub. A slow-acting stomach poison with moderate toxicity to mammals, it has longer residual activity than most botanicals. Toxicity to mammals is moderate.

Nicotine

Nicotine, derived from tobacco, is extremely toxic and fast-acting on mammals. Most organic certification programs do not allow the use of nicotine. The most common use is in greenhouses and to control soft bodied insects such as aphids and mites.

Neem

Neem, derived from the neem tree of arid tropical regions, contains many active compounds that act as feeding deterrents and as growth regulators. The main active ingredient is azadirachtin, which is said to be effective on 200 types of insects, mites and nematodes. It has low toxicity to mammals. Two trade names in are Margosan-OŽ (Grace) and BioNeemŽ (Ringer). Use is restricted to a few states where it has been registered to control whiteflies, thrips, and caterpillars on ornamentals. A neem solution cannot be exposed to direct sunlight and is effective for only eight hours after preparation. The water used in preparation should be 50 to 95 degrees F. It is most effective under humid conditions or when the plants and insects are damp.

Piperonyl Butoxide (synergist)

Piperonyl butoxide (PBO) is derived from sesame. Because it enhances the effect of many botanicals, PBO is more appropriately described as a synergist than as an insecticide. PBO inactivates enzymes on the bodies of insects (and mammals) that break down toxins. Using PBO reduces the amount of insecticide needed and increases the likelihood that insects will be killed rather than just temporarily paralyzed. Chronic exposure of humans to PBO can damage the nervous system.

SOAPS AND OILS

Soaps

Commercially available insecticidal soaps contain potassium or sodium salts of fatty acids. Soaps are effective in drying up soft-bodied insects only while the soapy liquid is in direct contact with the waxy cuticle of insects such as aphids and whiteflies. Commercial soap formulations such as M-PedeŽ are formulated to reduce damage the plant, but in some cases plant injury can still occur. Since there is no insecticidal effect of these soaps once they dry, growers sometimes rinse off the soapy residues.

This not only helps the plant, but the rinsing removes additional pests by physically washing them away. None of the soaps are very toxic to animals. Effects of the soapy liquid on beneficials vary, but since soap residues are harmless, soaps used before beneficials are introduced will not affect future emergence of beneficials from parasitized pests. Dishwashing soaps and detergents can also be effective against soft-bodied insects but have not been formally evaluated as pesticides and may damage the plant by breaking down the waxy layer protecting the leaf surface.

Horticultural Oils

Horticultural oils act by suffocating insects and eggs, disrupting insect metabolism, and repelling insects. They can control aphids, spider mites, scale, plant bugs, and lacebugs for up to a week after application. Horticultural oils are typically applied as a 2 percent solution in water. Although ultra-fine oils such as SunSprayŽ are generally considered safe for use on vegetables, they should still be tested on a small scale to detect possible plant injury on each cultivar prior to large-scale use. Plants in bloom and water-stressed plants are more susceptible to oil damage than nonflowering or unstressed plants. Oils and fungicides should not be tank-mixed or used within two weeks of each other to avoid toxic effects on the foliage. To avoid 'boiling' the plant in oil, horticultural oils should not be used when temperatures are above 90 degrees F.

By controlling aphids and thrips, oils have the potential to control virus spread. Oil sprays have been found to slow the spread of virus by delaying primary infection. Once 10 to 20 percent of plants are infected, however, oil may not be very effective in controlling further spread.

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