Posted on 28 November 2010 by

The Tomato Hornworm Beauty in Nature\’s Design

tomato_hornwormBy Mindy McIntosh-Shetter

This summer has been a unique one for any tomato gardener.

The cool and wet spring, dry summer temperatures and lack of rain along with insect infestations has been the norm it seems for the 2010 tomato season.

And the list does not stop there but for my dad the tomato season blues seemed to be never-ending.

First, as a seasoned tomato gardener, my dad decided to plant his tomatoes in planters. Two of these planters were near the house while the third was in the middle of the backyard. He staked his tomatoes in this third container and wrapped fishing line around the tomatoes to deter the deer.

But within a week his tomatoes in the third planter began to show signs of what my dad thought was deer damage. The vegetation that hung outside the fishing line as being stripped of both leaves and stems at an alarming rate but there existed no other signs of deer. A few weeks later the planters near the house began to show the same signs as the third planter. My dad could not believe the deer were coming that close to the house but…

Nature is a wonderful mechanism that if allowed to work without human interference can create the most beautiful and wonderful things. But sometimes the beauty of nature can be a pain to a human and that is where my dad’s tomatoes started being that is a pain.

So as my dad contemplated pulling up his tomatoes I decided to get to the root of the problem. As I headed to the third planter I saw the telltale sign gleaming in the sun. The whole problem was not deer but an ingenious design of nature that can be as big as a hummingbird, as small as a caterpillar, and a food source for an insect. What could this be? The simple answer to my dad’s gigantic problem was the invasion of the tomato horn caterpillar.

The tomato hornworm is the larva of a hummingbird size moth called five-spotted hawkmoth. This beautiful moth is gray-brown in color with yellow spots along the sides of the body. As soon as the five-spotted hawkmoth hatches it mates and lays eggs on the underside of tomato, pepper, eggplant, and potato leaves. The larva will appear on the plants in late June to August. These little mechanisms of plant destruction will consume leaves, stems, and sometimes even fruit.

If life is good for the larva it will wonder around the garden after 3-4 weeks feeding in search of the most perfect place to call home. When this is found they dig themselves in where they will turn into a pupa. This pupa will overwinter and hatch in the spring. Come spring the five-spotted hawkmoth will hatch and the process starts again. Two generations of tomato hornworms can be produced per year and for the tomato gardener that can spell disaster. But what can be done.

There does exists biological controls that can help control the tomato hornworm that is the Bt spray (Bacillus thuringiensis). This spray is applied to the top and bottom of the tomato leaves and is repeated every 5 to 7 days until you no longer se tomato hornworms. This spray is safe for animals, people and the environment but paralyzes the tomato hornworm so it starves to death. Another approach is the use of an insecticide soap that is simply sprayed on the underside of the tomato leaves when the moths first appear.

Another approach is what I call utilizing natures beautiful design. The first way is simply using a hard spray of water on the underside of the leaves. This heavy spray of water will simply dislodge the eggs and not allow them to hatch. Planting marigolds around the tomato garden is another approach. The olfactory protection that marigolds present keeps many different types of pests at bay. Also becoming one with the tomato plant is another way of organically controlling this pest.

Knowing your tomato plants and removing by hand pest can save the environment and help you develop your own plant diagnostic skills but… the tomato hornworm can be a curse and a good luck charm all in the same pest. Parasitic wasps (Braconid and Trichogramma) love to lay their eggs in the tomato hornworm and feed on the inside of the larva while paralyzing the tomato hornworm. They continue to use the tomato hornworms body until they hatch.

These parasitic wasps form a haven in the tomato hornworm, which turns out to be a positive omen that the garden spirits are keeping things in Zen balance. To keep this balance when the tomato hornworm is picked off keep the ones covered with white eggs. Place in a jar and feed fresh leaves daily. When eggs hatch release the parasitic wasp back into the environment to help keep the natural balance in order without destroying it.

Understanding nature and how the tomato garden fits in the larger scheme of things is crucial to the success of any garden and gardener. And as far as my dad’s garden that was a very valuable lesson that we all learned this summer. While the tomato hornworm did take a toll on my dad’s tomato crop it was only part of nature’s plan. So next time a pest invades the garden think about the overall scheme of it all not only how it affects you the gardener right now.

So until we blog again, may parasitic wasps police your garden and improve the Zen of the environment you look over.

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