Organic Sprays for Killing Hornworms

Actually a Moth Larva

• Hornworms are a large green caterpillar with a horn located at its rear that makes it easy to identify this leaf-eating worm. The hornworm is the larval stage of a hummingbird moth or a sphinx moth. These moths lay their eggs on the underside of leaves in the spring. The eggs hatch in about a week, giving way to the larvae that chews on foliage and fruit of the infested plant. The hornworm's feeding creates ragged holes in the foliage and fruit of plants and -- in heavy infestations -- can defoliate the plant.

Organic Bt -- Hornworm Stomach Poison

• Bacillus thuringiensis -- also known as Bt -- is an organic insecticide containing a bacterium found naturally in the soil. These bacteria act as a stomach poison that prevents the hornworm from feeding. Within a few days of consuming the bacteria, the hornworm starves and dies. Bt doesn't contain harsh or toxic chemicals that pose a hazard to humans and mammals and is safe for use around beneficial insects. It is applied as a foliar spray to plants infested with hornworms and is available in ready-to-use and concentrate formulas. Each brand of Bt has application instructions. Generally, 1 to 3 teaspoons of the Bt are diluted with 1 gallon of water before spraying the entire plant with the solution.

Spinosad -- "Bee" Careful

• Spinosad is a broad-spectrum insecticide that can be used in organic gardening. It contains a fermented soil bacterium that controls a wide array of pests through contact or ingestion. It has a low toxicity level to beneficial insects but shouldn't be applied when bees are active. Spinosad is non-toxic to humans but can cause eye irritation. It is also non-toxic to wildlife, birds and fish. Spinosad insecticides are available in ready-to-use, concentrate and granular forms. For ready-to-spray spinosad, attach a garden hose to the bottle and adjust the sprayer setting to a dilution ratio of 2 fluid ounces of the insecticide per 1 gallon of water.

Pick and Prevent

• Pesticides are not the only way to control hornworms. Pick off hornworms and place them in soapy water. Introduce parasitic wasps that lay their eggs on the caterpillar. When the eggs hatch, the larvae feeds on the worm, killing it. The best defense against hornworms is to use organic insecticide sprays in conjunction with mechanical methods.