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Tomato Hornworms… They’re Back!

As if growing tomatoes wasn’t difficult enough in South Florida, enter the spectacular Tomato Hornworm.

photo of Tomato Hornworm larva

Tomato Hornworm Larva

I say this, because it is a most attractive caterpillar, with it’s pronounced legs, bright green color and of course the horn!  Full grown, Tomato Hornworm can become as big and fat as your pinkie. To become so juicy and plump it needs to eat a lot.  Its favorite food is a tomato plant, as well as other members of the Solanaceae family. These include many landscape plants such as Brugmansia sp. (Angel’s Trumpet), Brunsfelsia sp. (Yesterday, Today and Tomorrow), as well as peppers and eggplants.

Tomato Hornworm is the larva of a Sphinx Moth.

The Sphinx Moth is a very large moth and is also known as Hawk Moth, or Hummingbird Moth.  It has gotten this name because if you’ve ever been outside at dusk and heard a buzzing close by, it may have been one of these moths.  Their wings beating sound much like a hummingbird.  They also have a long proboscis and sip nectar like a hummingbird does.

Most moths fly at night and these are no exception.  You may wonder, how do they locate their host plant in the dark?  Most butterflies and moths find their host plants through their sense of smell, which is why many moth pollinated plants are very fragrant (easier to find in the dark).  It is also why many have white flowers (easier to see in dim light).

Be a Good Scout!

Once a mated female finds her plant, she will deposit dozens of eggs, mostly on the tender growing tips.  So, when you are scouting, check for eggs there.  All insects are easiest to control when they are small, and eggs are easily rubbed off, if you can find them.

I recently planted a cherry tomato and it was getting big and beautiful, with lots of blossoms.  I went away for a week, and upon my return, it looked like the whole top had been eaten clean.  Nothing but stalks remained.  Upon close observation, I found there to be dozens of Tomato Hornworm larvae in varying stages of growth, munching happily, as if I had set the table just for them!

Masters of Camouflage

For a week, I went to check on it daily, and each day, I kept finding more!  Many butterfly and moth larvae have a natural camouflage and these guys are masters at it.  They blend in so perfectly, that it’s almost impossible to see them all.  Scouting, which is an important part of IPM (Integrated Pest Management) can work, but you must be diligent.

Follow the Frass

Frass is the excrement of caterpillars.  Often, you will see their frass, so follow the frass trail and when you find the caterpillars, pluck them off!  You can drop them in a bucket of soapy water, or into your pond for a tasty fish treat.  That’s what I do.  They don’t bite, and their horn is nothing but a smokescreen for predators.

BT works best

If you really want to make life easier during tomato season, nip them literally in the bud.  Use a biological insecticide called BT (Bacillus thuringiensis) at the first sign of them.  Spray the whole plant, leaves and flowers.  When a caterpillar eats these parts, it will become sick and die.

BT should control any caterpillars you miss while scouting until the next time they show up, in which case you would have to re-apply.  Happy Scouting.

2 Comments on “Tomato Hornworms… They’re Back!

  1. Is this BT toxic to the human being?…Are these moths in any danger of decline in numbers?

    • These are good questions; thanks for asking! BT is considered OMRI safe, but it’s always a good idea to wash your veggies and fruits prior to eating. As for their status as endangered; not at all. When it comes to your tomatoes; it’s either you or them, and you have to do something, or else, your plants will be decimated in short order. Here is an article that will give more details: https://edis.ifas.ufl.edu/pdffiles/IN/IN19700.pdf
      Hope this is helpful.

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