What is that giant green thing on my tomato plant?

What is that giant green thing on my tomato plant?

Last summer I was in my tomato patch, admiring the ripening tomatoes and pruning off excess growth, when something caught my eye. Now I should pause and explain that I grow a lot of tomatoes; 17 plants last season, in fact. And they aren’t little tomato plants—I love to grow heirloom tomatoes, many of which get to be more than 8’ in height. So I should probably have said that I was wandering through my tomato forest, when something caught my eye.

It was an unusual white stripe on the leaves of one of my tomato trees, right at eye level. The sun was high and bright, casting harsh shadows, so I couldn’t quite make out what I was looking at.

Manduca sexta tobacco hornworm under a tomato leaf

 

I peered in for a closer look…eek! That was no leaf, that was a tomato gardener’s nemesis—the tomato or tobacco hornworm!

Manduca sexta tobacco hornworm under a tomato leaf

These huge caterpillars have a correspondingly large appetite, and can defoliate a tomato plant (i.e. eat all of its leaves) if left unchecked.

Manduca sexta tobacco hornworm on a trowel

I first thought this particular specimen was a tomato hornworm, but a bit of digging revealed that it was actually a tobacco hornworm. While different, their habits are similar enough—they both feed on plants in the Solanacaea family—tomatoes, potatoes, and tobacco. Tomato hornworms are marked with 8 white v’s, tobacco hornworms are marked with 7 white stripes down either side. Tomato hornworms have dark blue or black horns on their backs (sort of a tail) while tobacco hornworms have red horns. You can clearly see the red tail and white stripes, not v’s, in the above photo.

Both the tomato hornworm and tobacco hornworm can seriously damage or even kill a tomato plant. Fortunately, given their size, they’re easy to spot (even in a tomato forest) if you inspect your plants regularly. Also,  you’re not likely to have a large infestation of them–I’ve only ever found one or two in my garden during a season–and most years I don’t find any. Despite having multiple legs, hornworms don’t move quickly, so hand picking them and disposing of them is the best method of control (drowning in a pail of soapy water is recommended by some gardeners). You do not need to apply a spray or powder or get into any of that nasty stuff.

While I don’t like what these critters do to a tomato plant, I do find them quite fascinating to look at. Not only do they have white stripes but they also have circular white and black markings that look like eyes all the way down their sides—I presume this is to confuse predators. If allowed to carry out their life cycle they turn into large moths.

Manduca sexta tobacco hornworm on a trowel

Have you ever been surprised by a tomato or tobacco hornworm in your garden?

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