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The Warning Sign That Could Spell The End Of Your Tomato Plants (Unless You Act Quickly)

Written by Author Tracey Besemer Published on August 13, 2024

Hoo boy. I get asked this question all the time by Rural Sprout readers. One minute, your tomatoes are doing fine, and then, within a day or two, you have skeletal tomato plants. Seriously, that’s all the time this common tomato nemesis needs to shut down your tomato season completely.

And the worst part is you’re probably looking right at it and don’t even know it.

Or, you’ve found this pest’s, ahem, “grenades,” and you’re wondering what on earth is going on with your tomato.

Tiny hornworm poop on tomato branch
It usually starts when you notice tiny barrel-shaped poop in the crook of a tomato stem.

In either case, what you’re dealing with is tomato hornworms.

These very hungry caterpillars make Eric Carle’s caterpillar look like it’s on a diet. Or, who knows, maybe the book was inspired by these same pests. All I know is they eat a lot, and they eat fast.

Tomato hornworms, also known as tobacco hornworms, are the larva stage of the five-spotted hawk moth, a truly beautiful moth, were it not for their penchant to eat your entire tomato plant.

The Five-Spotted Hawk Moth is so large it’s often mistaken for a hummingbird visiting flowers.

After snacking on your tomatoes, they poop everywhere, leaving their charming explosive-shaped excrement all over your garden while you work maddeningly to find the caterpillars and get rid of them.

Tomato hornworm “bombs.”

Unfortunately, by the time their excrement is large enough for you to notice, that also means you’ve got finger-sized caterpillars lurking among your tomato plants.

Hand holding a hornworm
Here’s a tiny little guy. They’re actually pretty cute if you ignore their destructive behavior. I found this guy easily with my tried-and-true hornworm spotting method. (Keep reading.)

I used to spray my plants with Bt (Bacillus thuringiensis) when I had a tomato hornworm infestation, but the problem with Bt is that it works best when the caterpillars are smaller than 2”.

At that size, they’re darn near impossible to see, and they haven’t made their handiwork noticeable yet. So, in theory, you need to spray before you even know they are there.

Even though Bt is a naturally occurring bacteria, I’m still not chuffed about the idea of spraying my plants with stuff if I don’t need to. (Mainly because that’s more work for me in an already busy time of year.)

But I don’t worry about tomato hornworms anymore.

I have found the easiest way to deal with them, and it’s so effective that I can find them and eradicate them (that means feed them to the chickens) before they’re even half an inch long. Want to know my secret?

Hands Down the BEST Way to Deal with Tomato Hornworms

You’re going to laugh when I tell you the solution. Or you’ll think it’s gimmicky (I did when I first heard of it), but you have to hear me out.

Get yourself a cheap UV flashlight on Amazon.

uv flashlight

Yup.  

That’s all you need.

Head out to your garden in the dark with your trusty UV flashlight and turn it on. You’ll notice that the tomato leaves look red in this light. And if you have any pesky tomato hornworms, you’ll notice that they fluoresce bright green under UV light.

hornworm at night lit up by uv flashlight
Oh, hi there, destroyer of tomato leaves. Yup, that’s the little guy pictured earlier in the article.

Bring a jar of soapy water with you and pluck them off your plants and into the soapy water. (Don’t worry, that big stinger-looking thing on the end is just for show. It’s 100% harmless. They can’t sting or bite you.) You can wear gloves if they give you the heebie-jeebies.

Don’t forget to check under the leaves, being careful not to shine the light in your eyes.

Important: UV light is extremely dangerous to your eyes. Under no circumstances should you shine a UV flashlight in someone’s face. You can do permanent damage to the eyes.

I usually start checking my tomatoes in July, as that’s when these larvae start to show up in my area. You’ll want to check with your local ag extension office to find out when they’re active near you. I do a routine evening check once a week throughout the rest of the growing season, and that’s frequent enough to find them before they can do any real damage.

This little guy would be impossible to see in the daylight, but all .5″ of him stood out as bright as day with my UV light. (Excuse the shakey photo, I was holding the flashlight and trying to take a picture at the same time.)

There are a couple of other garden pests that glow in the dark, too. You can read more about using a UV flashlight to patrol your garden for pests here and more about tomato hornworms in general here.

The Downside

There is one downside to this method for dealing with tomato hornworms. The chickens are rather upset with me. They used to enjoy fat, juicy caterpillars as big as my thumb. Now, all they get are a couple of teensy hornworms so small they have to scratch in the dirt to find them.

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Tracey Besemer

Hey there, my name is Tracey. I’m the editor-in-chief here at Rural Sprout.

Many of our readers already know me from our popular Sunday newsletters. (You are signed up for our newsletters, right?) Each Sunday, I send a friendly missive from my neck of the woods in Pennsylvania. It’s a bit like sitting on the front porch with a friend, discussing our gardens over a cup of tea.

Originally from upstate NY, I’m now an honorary Pennsylvanian, having lived here for the past 18 years.

I grew up spending weekends on my dad’s off-the-grid homestead, where I spent much of my childhood roaming the woods and getting my hands dirty.

I learned how to do things most little kids haven’t done in over a century.

Whether it was pressing apples in the fall for homemade cider, trudging through the early spring snows of upstate NY to tap trees for maple syrup, or canning everything that grew in the garden in the summer - there were always new adventures with each season.

As an adult, I continue to draw on the skills I learned as a kid. I love my Wi-Fi and knowing pizza is only a phone call away. And I’m okay with never revisiting the adventure that is using an outhouse in the middle of January.

These days, I tend to be almost a homesteader.

I take an eclectic approach to homesteading, utilizing modern convenience where I want and choosing the rustic ways of my childhood as they suit me.

I’m a firm believer in self-sufficiency, no matter where you live, and the power and pride that comes from doing something for yourself.

I’ve always had a garden, even when the only space available was the roof of my apartment building. I’ve been knitting since age seven, and I spin and dye my own wool as well. If you can ferment it, it’s probably in my pantry or on my kitchen counter. And I can’t go more than a few days without a trip into the woods looking for mushrooms, edible plants, or the sound of the wind in the trees.

You can follow my personal (crazy) homesteading adventures on Almost a Homesteader and Instagram as @aahomesteader.

Peace, love, and dirt under your nails,

Tracey
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