Posted on 17 June 2011 by urbangardencasual.com

A Tale of Two Species: The Tomato Hornworm and the Gardener

By Mindy McIntosh-Shetter

Every year I seem to get the odd looking caterpillar called the tomato hornworm on my tomatoes.

These little beasts always seem to appear over night with devastating affects.

Stripped stems poke upward and before I know it my tomatoes are stripped of all vegetation but is the organic gardener to do.

The first step is to recognize the pest. Some individuals feel it is deer damage or some other grazing type of animal consuming their crop.

But a telltale sign that it is a tomato hornworm is the fact that the vegetation will be missing from the top of the plant and will move downward. Also, this damage will start around midsummer and continue until the end of the growing season.

Next, the most obvious sign that tomato hornworms are present are the worms themselves. They are large, segmented, green worms that are between 3- to 3 ½-inches long. They have eight v-shaped markings on each side and a straight black hornlike structure at the end of their body.

Once the caterpillars are seen a lot of damage has occurred. But before you pull out the chemical spray to treat this problem try some organic approaches to the problem

Prevention

Preventing the problem before it occurs is an easy way of reducing the chances of inviting the tomato hornworm into the garden. One technique is to rotate crops in the garden. Tomatoes should not be planted in the same area for longer than 2 years and nothing in the nightshade family (Solanacous) should be planted in those areas either. Plants that fit this bill include eggplants, peppers, and tomatoes.

Another approach is to till the garden in the fall and spring. This will destroy any pupae that are in the ground.

During the Growing Season

The easiest approach to use once the tomato hornworm is spotted is to pick the caterpillars off by hand. After they are removed from the tomato plants, place in a bucket of warm water and dispose of down the drain or in the trash.

Or release parasitic braconid wasp (Cotesia congregatus) into the environment. This type of wasp will lay its eggs on top of the tomato hornworm. The eggs will hatch and feed on the caterpillar. They will then pupate on top of the tomato hornworm creating small, white cocoons that appear on the back and sides of the caterpillar. Once they have reached this stage, the caterpillar is paralyzed and can no longer harm the plant. If left on the plant, the white cocoons with hatch and release more parasitic wasp into the environment. These new wasps will then affect more tomato hornworms.

Another natural predator of the tomato hornworm is the common wasp (Polistes). This little insect kills and feeds on the larvae of this caterpillar.

Repel Them

The last approach is to repel the caterpillars away from the tomato plants. This is done by creating a spray that not only smells but also tastes terrible. Many different recipes exist but the one that I have found the most success with is the following.

Spearmint Hot Pepper Horseradish Spray

Ingredients

¼ cup of hot peppers
½ gallon of water
¼ cup fresh spearmint
¼ cup horseradish, both the roots and leaves
1 Tablespoon liquid detergent
¼ cup green onion tops

Directions

Mix hot peppers, spearmint, horseradish, and green onion tops in a blender with enough water to cover. After it is blended, place the solution in a plastic bowl and let set for 24 hours. Then, strain the mixture and mix with ½ gallon of water and add 1 tablespoon of detergent. Place in a sprayer and apply. If any of the solution is left, store in a cool place for a few days. Reapply after it rains.

So if your tomato plants get a visit from the hummingbird moth this summer, no need to worry, just try one of these techniques to control and conquer them their offspring, the tomato hornworm.

So until we blog again, organic control is all ways the best way to go. With a little effort and some time, we can create a better environment on a dime.

Check out out our sister site Tomato Casual for more tomato info.

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