Found in almost all of North America, the tomato hornworm is one of the most devastating garden pests. This creature consumes not only tomatoes, as the name implies, but also entire pepper, eggplant, potato, and even tobacco plants.
Known scientifically as Manduca quinquemaculata, this creature eats the leaves, fruits, and even stems of various plants. Even though the pest is relatively large, it can be difficult to find in a garden due to its camouflage coloring.
As a gardener, it’s important that you understand the unique characteristics of the tomato hornworm. Only then can you equip yourself with the skills and tools necessary to rid yourself of this destructive pest.
How to Identify the Tomato Hornworm
The tomato hornworm looks a lot, to the untrained eye, like a large caterpillar. About four inches long, this pest is green with seven white stripes. These stripes are diagonal.
Where does the name “hornworm” come from, you might ask? If you are lucky- or rather, unlucky! – enough to view one of these pests in your garden, you will note that it has a large red or black horn protruding from its rear.
The tomato hornworm is actually the juvenile state of a heavy-bodied moth. This month ends up having a five-inch wingspan and is known as a hawk moth. It can also be referred to as a sphinx moth. A quick-flying moth, this creature hovers in a manner like a hummingbird and has white stripes or brown spots.
It can be difficult to determine whether the tomato hornworm is the pest you are dealing with, as signs of an infestation are often similar to those from other pests. However, if you have a tomato hornworm problem, you will likely find larvae among the plants.
You may also see their black droppings on the leaves of your plants. Sometimes, you will be able to see the pests moving, as they have a tendency to thrash.
Tomato hornworms often come out at dusk, dawn, or during the night to feed. They will stay right out in the open as they feed, leaving behind black droppings. Otherwise, they are easily camouflaged by their color.
You can often convince them to come out during the daylight hours by spraying them with the intense blast of a garden hose, though!
Rather than boring through the plant entirely, tomato hornworms will eat superficially. They will leave behind large, open scars – or often a void where they have eaten with no plant matter left at all.
Hornworms need gardens to survive – in fact, they need broad leaves and soft soil just to survive. You won’t find them living in the forests but instead only in gardens. This is part of what makes this pest so difficult to eliminate. It isn’t going to give up easily, as it doesn’t have many other places to live.
Why Tomato Hornworms Are Unwanted in the Garden
If you’re reading this article and have never had to deal with tomato hornworms, you might be thinking, “Ok. So you have caterpillars in the garden. What’s the big deal? Can’t you just let them be?”
Unfortunately, you can’t. While tomato hornworms usually choose to inflict their damage on tomato plants, they have also been known to attack eggplant, potatoes, and peppers. There are many other weeds that can host these pests, too, including jimsonweed, nightshade, and horsnell.
These pests have two life cycles per year, and since they reproduce rapidly, it does not take long for them to overtake your garden. They can rapidly defoliate your plants and begin feeding on the upper portions of the plants – they are difficult to spot at first.
In fact, you might not even realize you have a problem with tomato hornworms until your plants are almost completely defoliated! As these pests feed, they will leave droppings everywhere. They can not only remove the leaves your plants need to be healthy, but they can destroy fruit, too.
The Life Cycle of a Tomato Hornworm
The tomato hornworm has a long life cycle compared to other pests of this nature. Tomato hornworms overwinter in the soil as brown pupae, with moths emerging in the late spring.
These adults will mate and then deposited eggs on the undersides of leaves. The eggs hatch in just five days, with the larvae passing through five or six distinct stages before they reach their full growth at four weeks. The larvae then burrow back into the soil.
There are usually two generations of tomato hornworms per year, with this cycle repeating itself.
You don’t need to worry about the moth version of the tomato hornworm, or the sphinx moth. Adults feed on nectar from flowering plants and won’t go after your vegetables.
How to Get Rid of Tomato Hornworms
There are several methods by which you can get rid of tomato hornworms.
Most gardeners opt for the simple handpicking method. To do this, you will need to be vigilant about your garden and make sure you walk through it repeatedly each week to check for the pests.
Once you remove the pests from the plants (which is easy enough to do, since they are so large), you should drop them into a bucket of hot, soapy water to kill them.
If you find that handpicking does not work well to control populations, you have several other options. For starters, you can use a short-lived pesticide to get rid of them.
You might want to consider spinosad or even Bacillus thuringiensis. Both of these are short-lived and natural. They tend to be highly effective on young caterpillars.
Bacillus thuringiensis, or BT, is particularly effective. BT is a natural bacterium that is found in soil. When hornworms consume the bacteria, it causes severe paralyze of the caterpillar’s digestive system. As a result, the pest will stop feeding and eventually die off.
BT is a desired method of treatment for many gardeners because it does not impact humans at all. It’s a natural substance that is super effective, particularly when the larvae are small.
If you don’t want to use chemicals in your garden, another way you can kill tomato hornworms in an organic way is to mix up a combination of liquid soap and water.
Spray the mixture on the plant foliage before adding some cayenne pepper – this will get rid of the bugs and then repel them into her true. Just keep in mind you will need to repeat this treatment after each rainstorm.
Once you have populations under control, it might be worth your time to release some beneficial insects. Consider releasing ladybugs or lacewings to the garden.
These bugs can be purchased online or at local garden stores and are effective because they eat the eggs. These bugs should e released when pest levels are low so that the beneficial insects have a chance to establish control.
Another predator to consider is the paper wasp. This common wasp feeds on a variety of caterpillars that may be causing issues in your garden. If you’re not 100% sure that it’s the tomato hornworm giving you grief, then the paper wasp might be the way to go.
There are other wasps and predatory species that can parasitized tomato hornworms, too. One of the most common is the braconid wasp.
This small wasp lays eggs on the hornworm and they then feed on the inside of the hornworm. The adult wasps will emerge from the hornworm eventually and destroy the hornworm as they do so.
If you see a hornworm covered with white egg sacs, leave it be. This is a sign that the tomato hornworm has been infested with its own invaders – parasitic wasps.
The egg sacs are those of the braconid wasp, a beneficial parasitic wasp that will eventually consume the tomato hornworms in your garden.
You can also sprinkle some diatomaceous earth around your garden. Diatomaceous earth is nontoxic and is instead made up of tiny aquatic organisms that were fossilized.
Under a microscope, diatomaceous earth looks just like broken glass. However, it’s not harmful to people or animals, since the pieces are so small. It kills the insects instantly as they walk over it, scoring their outer layers and causing extreme desiccation.
Finally, there are several chemical insecticides you can use to get rid of tomato hornworms. These easily control hornworms but may not be desirable for organic gardens.
That being said, options like Sevin Insecticides are nonsystemic, meaning they don’t penetrate plant tissues. You can wash them off after they have done their job.
Preventing Tomato Hornworms in the Future
If you find that your tomato hornworm problem keeps coming back, you may need to enact some more permanent preventative measures. Tilling after harvest is effective, as it will destroy the pupae that overwinter in the soil.
Since the pupae are so large, this method is effective – the pests aren’t buried deeply in the soil, which is the case with similar pests. You can usually kill up to 90% of the pests with this method.
Crop rotation can also be an effective method of preventing tomato hornworms. Since these pests only go after certain plant species, like tomatoes and peppers, you can reduce the frequency of infestations by cycling these plants out of your garden. You will, in essence, be removing their food source.
Weeding on a regular basis can also help keep populations of tomato hornworms down. This will remove the number of sites where the pests can overwinter and lay eggs. Tilling will destroy burrowing caterpillars, and weeding will eliminate their eggs.
Some people have used traps to reduce moth populations, which can be effective in limited cases. These traps are used to lure adult moths into blacklight.
Once the moths are inside the trap, they can be killed or released in another location. There is limited evidence that these work, but if you are trying to reduce populations of other kinds of moths, it might be worth a try.
When you find tomato hornworms in your garden, be careful of how you dispose of them. The best way is to kill them in a bucket of soapy water, as mentioned previously.
Some people argue that they can be composted, but it’s best to err on the side of caution here – you don’t want a couple to live and continue to breed, furthering the cycle of infestation.
Why You Need to Get Rid of Tomato Hornworms for Good
Left to their own devices, tomato hornworms have the potential to wreak some serious havoc on your garden. These pests have voracious appetites and will easily defoliate a plant in just a few days.
If detected early on, you can get rid of these pests -but left unfettered, you may have a serious infestation on your hands.
Luckily, tomato hornworms are large enough where manual elimination is possible. However, if you can’t get rid of these pests by handpicking, you may need to consider some of the methods described above.
As always, following best practices as a gardener and caring for your plants on a daily basis can help you stay on top of any problems with pests – before they even become problems.
Rebekah is a part-time homesteader. On her 22 acres, she raises chickens and bees, not to mention she grows a wide variety of veggies.