Natural Pesticides for Vegetable Gardens

Pesticides made from natural ingredients are approved for use on organic gardens. Although in some cases they may not work as well as more toxic chemical pesticides, they are generally safer to use. The most widely used natural pesticides range from useful bacteria to soaps and active ingredients extracted from plants.

While preparing and applying any pesticide, wear protective clothing, including a long-sleeved shirt, long pants, socks, shoes, protective eyewear and chemical-resistant gloves. Wash the gloves before removing them from your hands. 

If you get pesticide on your skin, wash your skin with soap and water. If you get it in your eyes, flush your eyes with water.    

Do not apply any pesticide when bees are in the vicinity of plants. 

Do not apply pesticide on a windy day because it drifts. 

Do not breathe or ingest any pesticide. If you do, call a physician or the National Poison Control Center 24/7 hotline at 1-800-222-1222.

Do not store a pesticide near heat or an open flame.

Bacillus thuringiensis, also referred to by the initials Bt, is a spore-forming bacterium that creates a hole in an insect's stomach, spilling the contents into the body cavity. The insect stops eating and dies in a few days.

Different varieties of the 20 subspecies of Bt are effective for killing beetles, butterfly larvae, which feed on leaves, and the larvae of flies, gnats and mosquitoes. Match the type of Bt you use with the insect that you want to control.

A Bt formulation often contains a surfactant to help it cling to leaves. The label of one Bt product -- formulated to kill insects such as cabbage loopers, red-humped caterpillars and leaf rollers -- calls for mixing 1/2 to 4 teaspoons of the product with 1 gallon of water. Apply that solution with a mist blower, pressurized sprayer or sprayer at the end of a hose, spray the solution directly on the target insects on vegetable plants. Cover the tops and bottoms of the leaves with the solution, but don't use enough to make it run off the plants.

Bt deteriorates in two to three days. So you may have to repeat the application once each week as needed.

Stay out of your garden for four hours after applying Bt. You can harvest and clean your vegetables with no waiting period afterward.

Commercial insecticidal soaps, which are highly refined versions of liquid dish soap, are made by combining alkali with plant or animal fatty acids. Additives in dry detergents formulated to wash clothes or dishes make them too harsh to use on plants.

Insecticidal soaps work best on aphids, mealybugs, scale crawlers, spider mites, thrips and other soft-bodied insects.

Some plants are sensitive to insecticidal soap. They include the tomato plant (Lycopersicon lycopersicum), which is usually grown as an annual.

Insecticidal soaps are typically available in concentrated forms that need to be mixed with water to create a 1 to 2 percent solution. Mix 2 1/2 to 5 tablespoons of a concentrated insecticidal soap with 1 gallon of water in a backpack sprayer. Apply the solution when you see signs of insect infestation, spraying it in early morning or late afternoon on the tops and bottoms of leaves. Do not apply it in full or direct sunlight or when the temperature is above 90 degrees Fahrenheit.

There are no garden re-entry or harvest wait restrictions for insecticidal soap. It can be reapplied in four to seven days if necessary.

Before you use an insecticidal soap in your garden, test the sensitivity of your vegetables to it. Spray it on a small portion of your vegetables, and wait one day to see whether or not they were harmed.

Neem oil is most effective on caterpillars, which are the larval stages of butterflies and moths, and on the larval stages of aphids, mites, cucumber beetles and Colorado potato beetles.

Neem oil contains the toxin azadirachtin, derived from the neem tree (Azadirachta indica), which is native to Central America, Madagascar and Africa and hardy in U.S. Department of Agriculture plant hardiness zones 10 through 12.

Neem oil typically is made by using alcohol or water to extract azadirachtin from crushed neem leaves. Concentrated commercial formulations are mixed with water for spraying on plant foliage.

Mix a neem oil formulation with water before using it. Mix 2 tablespoons of 70 percent neem oil with 1 gallon water that is warmer than 45 degrees Fahrenheit. Spray all surfaces of the affected plant, including the bottoms of leaves, until they are thoroughly wet. The solution can be reapplied every seven to 14 days.

Stay clear of your vegetables for four hours after applying a neem oil solution to it. You can harvest the vegetables after that time.

A byproduct of fermentation, spinosad is used to control the larva of butterflies and moths, including gypsy moth and codling moth, plus Colorado potato beetle larva and armyworms, borers, gall midges, fruit flies, leafminers, squash vine borers and thrips that feed on treated foliage. It kills within one to two days and does not significantly harm beneficial green lacewings, minute pirate bugs, predatory mites and lady bugs.

Commercial product that is 0.5 percent spinosad

Tablespoon not used for food

Hose sprayer

Shake the container of a commercial product that is 0.5 percent Spinosad, mixing the container's ingredients well.

Mix 4 tablespoons of the spinosad product with 1 gallon of water in the reservoir of a hose sprayer.

Spray the mixture on both sides of vegetable plant leaves until it runs off. Don't apply more than 3 gallons of the mixture per 1,000 square feet.

Stay out of your garden four hours after the application. Wait one day before harvesting vegetables. The spinosad-water mixture can be reapplied in three to 10 days, depending on the vegetable and pest being treated; check your spinosad product's label for its specific reapplication information.

Naturally occurring sulfur is less often used to control chiggers, mites and thrips than it is to prevent and control black spot, leaf spot, rust and powdery mildew on vegetables and other plants. It is sold as a dust to sprinkle on vegetables and as a powder to mix with water and spray on vegetables.

Apply it when you first see signs of insects. Repeat the application every seven to 10 days throughout the growing season. Do not apply it when the temperature is above 85 degrees Fahrenheit.

Dust wettable sulfur thoroughly on all parts of vegetable plants. Mix 4 tablespoons of it with 1 gallon of water to apply it from a hose or backpack sprayer, and wet vegetables thoroughly with the solution. Stay out of the treated area for 24 hours. You can safely use sulfur up to 24 hours before harvesting vegetables.

For more suggestions, see "Homemade Pesticides for Vegetable Gardens."

Use a plastic sprayers for sulfur because it erodes some metals. Don’t let it get in your nose or eyes. Also avoid getting it on your skin, which it may irritate.