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General Information

Insecticides have more potential for abuse and hazardous consequences of any garden chemicals. There are some considerations one should undertake to minimize undesirable outcomes. First don't use one unless it is absolutely indicated. You also must also identify the insect and the plant on which it is located and make sure both are  listed on the insecticide label. There is no one insecticide which is labeled for all insects and all plants.

Consider what the toxicity may be to humans, pets, wildlife and beneficial insects. Determine how long it persists in the environment and whether it spreads to groundwater.

Insecticides are classified according to their mode of action, and there are many classes. In recent years there has been a general retreat from the usage of the more harsh synthetic chemicals such as the organophosphates and a greater emphasis on more "biorational" insecticides. These are preparations that effectively controls pests and are derived from biological or natural origins.

The chemical categories and examples of the most used insecticides by homeowners in the US are listed in the table below

Types of Insecticides

Insecticide category

Example

Comment

Organophosphate

malathion, acephate

Moderately long persistence and potential toxicity to mammals and beneficial insects

Carbamate

carbaryl (Sevin)

Less persistent, broad spectrum effect on many insects, including beneficials, potentially toxic to mammals

Pyrethrum

pyrethrum

Extracted from a type of chrysanthemum, very brief duration and low toxicity to mammals and other animals

Pyrethroids

pyrethrum
derivatives such as biphenthrin, cyfluthrin

Longer duration of activity than pyrethrum, which varies by preparation. Broad spectrum insecticidal effect. Widely used in agriculture.

Neonicotinoids

imidacloprid, acetamiprid

Absorbed by plants as drench or spray for extended systemic effect on many insects. Low mammalian toxicity. They may have an adverse effect on honey bees and are banned in Europe

Microbial insecticides

Bt, or Bacillus thuringiensis

Several varieties of Bt are available, specific for different insects. They attack the insects intestinal tract. One variety effective for true caterpillars another is effective for mosquitoes and fungus gnats. virtually non-toxic.

Microbial derived insecticides

spinosad

Effective against leaf chewing insects, thrips and some others. Low toxicity to humans and non-target insects

Horticultural oils,
petroleum based

Highly refined oils

Kill insects by smothering them. Effective at different concentrations for both over-wintering insects such as scale and aphids and a host of others in summer.

Horticultural oils, vegetable based

neem oil, citrus oil extracts and several others

In addition to having an oil effect as above, Neem oil may have additional insecticidal and antifungal effects. Very low toxicity. Neem is a good choice.

Insecticidal soaps

fatty acid salts

Effective for small soft bodied insects such as aphids, thrips, juvenile scale, spider mites and others. Must come in contact with insect where it disrupts membranes. No residual, no toxicity to people, wildlife or good insects. Can be phytotoxic to some plants listed on label.

Miscellaneous

Botanicals-rotenone, azadarachtin (neem product)
Growth regulators—several                     
Minerals and related-sulphur, boric acid

 Non-Insecticide strategies

The single best insect control measure is to purchase plants resistant to the pests commonly found. It is not always possible, but always consider this when selecting new plants. Many of the pests and their eggs over-winter in trash, such as squash vines, left from the previous growing season. Weed near the garden are a refuge for pests such as spider mites which may over-winter in the weed Henbit. Sanitation, with careful clean-up at season’s end and elimination of weeds can be a very effective pest control.

A jet of water will remove many of these pests. Depending on the situation, the larger ones may be removed by hand. Barriers are useful. Paper barriers around some vegetables will prevent cutworms.  Row covers over other vegetables will block out flying insects.

Useful Organic insecticides

Always try to use environmentally friendly organic insecticides first. This group includes insecticidal soap, horticultural oils, insecticidal bacteria, Neem products, Pyrethrin and others. Many of these products are sold with labeling for vegetables, as well.

          Insecticidal soap

Insecticidal soap is useful for soft bodied pests such as aphids, scale crawlers, white flies, spider mites. They work by contact and damages the insect’s outer covering. The downside is the short duration of activity requiring application every 4-7 days. They may damage some plants (phytotoxicity); sensitive plants are listed on the label. Household detergents are also insecticidal, but they tend to damage plants more than the commercial product.

          Horticultural oils

Horticultural oils have a long history of effective usage. Oils are produced from both petroleum and vegetable sources. Newer refined oils may be used both on dormant plants in winter and growing plants in summer, albeit in different concentrations. They are very safe around pets and children. Some plants, which will be listed on the label, are intolerant of oils.

Oils are effective for pests such as scale, aphids, whiteflies, spider mites and others, but generally are safe for flying insects such as bees. Oils smother insects and their eggs. Used in late winter, they may kill overwintering pests and their eggs along with some fungal spores. Oils may be the best insecticide for spider mites on vegetables (especially tomatoes) if used early and used regularly, according to the label.

          Neem Products

Products made from seeds of the neem tree in India are useful and very safe for insect control. Neem oil preparations have the same usage and implications as horticultural oil described above. Neem seed oil has another chemical Azadirachtin, which is not found in the purified neem oil and is sold as a separate product. It must be eaten by insects and causes to cease feeding. It is useful for a wide spectrum of insect control.

          Bacillus thuringiensis

Bacillus thuringiensis (Bt) is a bacterium toxic only to insects. It must be eaten by the insects in which it fatally infects their intestinal tracts. There now are at least 7 versions of Bt, each with its spectrum insect sensitivity. The type most available, Bt kurstaki, is effective for almost all of the caterpillars in the lawn and garden. It is safe for all animals and fish. A separate version, usually available, is effective for mosquito larvae.

It is slow to have an effect and some users will conclude it is not productive. Bt degrades easily and must be reapplied often. It is widely used in production of food crops.

Systemic Insecticides

          Imidacloprid

This insecticide is used as a soil drench or a spray and is helpful for control of many insects. It is absorbed by the plant and has a long duration of effect. It's effects on metablolism in insects is not shared with other animals, so toxicity is very low. It is safe enough to animals, that it is given in small doses orally to pets for flea control. Insects must feed on the plant for it to be effective.   

Because of the systemic effect, imidacloprid is useful for many of the borers of plants which are difficult to treat otherwise. Usually a drench applied to a tree or shrub, according to labeled directions, is useful for the entire growing season.
         
          Acephate

Acephate is found in the commercial brand of Orthene. It is another systemic but doesn’t last beyond 10-15 days. It has a wide range of effectiveness and low toxicity.

Synthetic Chemical Insecticides

There are many synthetic chemical insecticides. Most are absorbed by contact or insect feeding. They tend to have a long duration of activity and often are harmful to the beneficial insects. They may be very toxic to other animals, including humans.

These insecticides serve a very important function, both in agriculture and in our landscape. They are so diverse in their mechanisms of action and indications for usage, that they cannot be covered individually in this document. In your decision making, for pest control, always consider these products only after the other more environmentally friendly insecticides have been considered.

It is extremely important to read and follow the directions on the labels of all insecticides; it is especially true for this group. They should never be used on any insect or any plant unless specifically labeled for th