Monday, December 23, 2013

Natural Insect Repellents For Gardens

Natural insecticides provide effective control of aphids.

Natural insect repellents are largely derived from plants and minerals. Generally, natural pesticides do not accumulate in soil or in the tissues of humans or animals. Though derived from natural sources, they can still be toxic to mammals and beneficial insects. The use of natural insecticides and repellents should be a last resort after preventive, cultural and other organic practices have been implemented.

Botanical Pesticides

Ladybugs provide natural pest control.

Nicotine sulphate, an extract of tobacco, controls sucking insects on most vegetables, fruits, flowering plants, shrubs and trees. Do not use nicotine sulphate on roses. Nicotine sulphate is toxic to warm-blooded animals and is readily absorbed through the skin. Wear protective clothing to avoid skin absorption. Nicotine sulphate is sold under trade names Black Leaf 40 and Tender Leaf Insect Spray.

Rotenone is derived from the roots of several tropical plants. It is a widely used, natural insecticide and is effective against caterpillars, aphids and a number of beetles. In emulsified concentrated or powder form, Rotenone can be toxic to humans and fish; take precautions when using this insecticide. Trade names include Rotenone and Rotenone ME.

Mineral-based Pesticides

Snails are deterred by copper stripping.

Sulfur controls populations of spider mites, psyllids and thrips on most vegetable and fruit plants. Do not apply sulfur to plants when temperatures are over 90 degrees Fahrenheit; plant injury will result. Phototoxicity may occur if sulfur is applied where other pesticides have been applied within 20 to 30 days. The interaction between pesticides makes the plant more sensitive to sunlight. Leaves of the plant can become sunburned. Contact with sulfur may cause eye and skin irritation. When mixing or applying sulfur, wear protective eyeglasses and clothing. Trade names for sulfur include Cosan, Crisazufre and Hexasul.

Bordeaux mixture is produced by a reaction to copper sulfate and calcium hydroxide. Though naturally derived, Bordeaux is not approved for use in certified organic gardens. Bordeaux is an effective snail and slug repellent. Bordeaux trade names include Bordeaux Mixture, Bor-Dax and Copper Hydro Bordo.

Kaolin clay is a common mineral and is generally regarded as safe by the U.S. Food and Drug Administration. Kaolin clay is reported to be effective against apple maggot, white apple leafhopper, pear psylla and other fruit-tree pests. Surround WP is the primary trade name of kaolin clay.

Insecticidal Soaps

Insecticidal soaps are salts derived from fatty acids. Insecticidal soaps are effective against aphid, mealybug, whitefly, mite and other soft-bodied species when sprayed directly on the pest. Ammonium-based soaps should not be sprayed on edible portions of the plant. Insecticidal soaps have low toxicity to mammals. Cucumbers and some ornamental plants may be sensitive to phytotoxic effects of insecticidal soaps. Trade names of insecticidal soaps include Safer Insecticidal Soap, M-pede or Concern Insect Killing Soap™.

Horticultural and Vegetable Oils

Horticultural oils are plant- or petroleum-based oils. Horticultural oils smother soft-bodied insects on contact.

Neem is a horticultural oil derived from the neem tree in southern Asia. Neem provides effective control of gypsy moths, leaf miners, sweet potato whiteflies, western flower thrips, loopers, caterpillars and mealybugs. Neem has low toxicity to mammals. Neem oil is the active ingredient in the products labeled as Trilogy for food crops and Triact for greenhouse and ornamental plants.

Vegetable oils are derived from oil-seed crops such as canola and soybean. Vegetable oils smother soft-bodied insects on contact. Organic gardeners can make their own vegetable oil mixture for pest control.

As they have little residual effect, horticultural and vegetable oils have limited effects on beneficial insects.

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