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Growing Wisdom

How to identify and control tomato hornworm and other garden insects

I'm going to write this blog about vegetable gardens, but before you think this won't help you because you don't grow your own food, keep reading. Many of the same issues those of us who grow vegetables show up in the other parts of the garden.

Aphids for example can colonize on the tips of basil, but also love the the new growth of rose bushes. Some of the soil born pathogens we find in the vegetable garden can also harm plants in our flower borders.

Japanese beetles can shred the leaves of your favorite ornamentals and show up on the leaves of corn.

There is one pest that is found mostly in the vegetable garden and this is the tomato hornworm. The hornworm is a very large green caterpillar and due to its size can do a lot of damage seemingly overnight.

The image below shows what an adult hornworm looks like. The worms are a bright green that very closely resembles the same shade of green as a tomato plant's leaves. This makes these pests quite difficult to detect.

Sometimes a parasitic wasp will lay eggs in these worms and you'll notice rice like growths coming out of the back of the wasp. The larvae of the wasp basically eats the insides of the worm and kills it. The braconid wasp is a beneficial insect in the garden so if you kill the horn work with the wasp larvae then

Another way to find where the pest is hiding is to search for the poop. This is called black frass. Sometimes I see the damage from the hornworm, but I can't find the worm itself. However, I can often find the poop at the base of the plant or on the leaves just under where I will ultimately find the caterpillar.

When the caterpillar becomes an adult it turns into a sphinx moth. This moth is also known as a hummingbird moth because the speed of its winds make it appear like it's a small hummingbird. There are more than one type of hornworm and therefore multiple kinds of sphinx or hawk moths. Another famous one is the tobacco hornworm. The worm, unlike other insects can eat the leaves without the harmful effects of the nicotine.

Controlling Insects
I really like to use organic controls whenever possible in the garden and even then sparingly. Remember, an organic product that will kill a hornworm will also kill a monarch butterfly caterpillar. That said, if you find it necessary to use something on your garden try products with Bacillus Thuringiensis or Spinosad. Also Neem oil can be an effective ingredient.

Photo Credits:

Tobacco hornworm: Stephen Younge

Tomato hornworm: Paul M. Choate, University of Florida

Hornworm with frass: Oklahoma State University

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