Tomato Horn Worms

If you missed the email with pictures of the tomato horn worm, here’s a link from Colorado State University with more pictures of horn worms in all stages of life.  If you visit this site and scroll about half way down the page, you’ll find an image of the horn worm egg on the underside of a leaf.  Obviously the best control would be to find the egg and destroy it before the caterpillar hatches.

I’m also including some images  of horn worms and their “frass”  found on my potato and tomato plants and some from the Y gardens.  Judging by the leafless stems on many of the tomato plants in the various plots, there are still a lot of horn worms on the loose.  Maybe we should offer a bounty for the most captured – should we post a “wanted – dead or alive” poster for this destructive guy?

The one shown on the dead leaf is about 2″ by .5″ diameter and is easy to see on the dead leaf.  However, on potato or tomato plants, they are really hard to spot. The images of what is known as insect “frass” (a scientific name for “poop”) are from a mature worm.    So if you see this on your plant leaves start hunting for the culprit.   When the worm first hatches, its “frass” will look like dirt on the leaves.  At that stage, the worm is less than 1/32″ in diameter.  In about 2 weeks it will grow to this big size shown and larger.  And guess what fuels that growth – your tomato plant leaves and tomatoes.  If you see stems on your plants that have been denuded, start looking for the “frass”.  It takes patience and some practice, but you can find the ravenous green monsters, lurking on a stem, under a leaf or even on a tomato.  If they have the eggs on their backs you should let them live so the beneficial parasitic wasps can hatch.  Otherwise, you can put it in a jar with some sacrificial leaves and wait for it to complete its life cycle.  It would be a great educational experience for your children.  Just make sure you release the moth a long way from the tomato and potato plants belonging to you and to your neighbors.  Or you can avenge yourself for the havoc wrought by squashing it.  I’ll warn you,  it’s messy!


2 responses to “Tomato Horn Worms

  1. Would you believe we are picking hornworms off our plants and we check each plant everyday.

    • I would believe it. It’s amazing how many we found and over weeks, maybe months. Now I’m finding squash bug eggs on tomato plant leaves from neighboring squash plants. I think I”ll be lucky to get a single squash from 4 plants. But at least I’m learning what to look for and hopefully I’ll have better luck next season.

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