How to Kill Tomato Hornworms Organically + Prevention Tips
on Jul 14, 2021, Updated Oct 28, 2023
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If you’re wondering how to kill tomato hornworms, this post is for you! Here are six different ways you can kill them, plus tips and tricks to break the cycle to try to keep them from returning next year.
How to Kill Tomato Hornworms Organically + Prevention Tips
Hornworms are nasty looking HUGE green worms. They can get up to 4 inches long and look vicious! Don’t worry though – they aren’t likely to bite or sting you, but they will hurt your tomatoes and other nightshade plants.
- How to Kill Tomato Hornworms Organically + Prevention Tips
- The Life Cycle Of The Tomato & Tobacco Hornworm
- What Damage Do Tomato & Tobacco Hornworms Cause?
- How To Kill Tobacco or Tomato Hornworms
- How To Break The Lifecycle of The Tomato Hornworm
- How To Control Hornworms In The Future
Welcome to the HOW TO KILL GARDEN PESTS SERIES!
Who knew gardeners could take such pleasure in murdering annoying garden pests. If you garden, you’ll want to check out on the posts in this HOW TO KILL series. I’m adding new posts to this series each week, so subscribe to my newsletter if you want to know when they’re ready!
- How to Kill Cucumber Beetles
- How to Kill Potato Beetles
- Murdering Japanese Beetles
- How to Kill Cabbage Worms
- How to Kill Tomato Hornworms
- Controlling and Preventing Squash Bugs
- How to Get Rid of Squash Vine Borers
What Is The Difference between Tomato & Tobacco Hornworms?
There are actually two hornworms that attack tomatoes:
- Tomato hornworm, Manduca quinquemaculata
- Tobacco hornworm, Manduca sexta
They look pretty similar. They’re both huge, nasty beasts that cause utter destruction to plants in the nightshade family: tomatoes, potatoes, eggplants, and peppers. The easiest way to tell them apart is by their horn.
What are Tomato Hornworms?
Tomato hornworms have a black horn and v-shaped white markings on their abdomen. They are supposed to be more common in the Northern United States.
What are Tobacco Hornworms?
Tobacco hornworms have a red horn and white stripes – diagonal lines – on their abdomens. That means, most of the hornworms I have in my garden are actually tobacco hornworms and not tomato hornworms, even though tobacco hornworms are supposed to be more common in southern states.
Honestly, it doesn’t much matter which type you have. If you find these huge green caterpillars, you need to get rid of tomato hornworms before they completely defoliate your plants. Hornworms of all types are a terrible garden pest.
The Life Cycle Of The Tomato & Tobacco Hornworm
The adult forms of hornworms are known as sphinx moths or hawk moths, types of hummingbirds moths.
These large moths emerge toward the end of spring where they mate and lay up to 2000 hornworm eggs at night on plant leaves over the next 20 to 30 days.
The eggs will hatch in less than a week and begin eating tomato leaves. If tomato leaves are not available or they have been consumed, the hornworms will eat related veggies for up to one month.
The hornworm will then pupate after burrowing into the soil for another week where it will emerge ready to mate and lay more eggs. Multiple generations per season are common.
Hornworm grubs are big, brown, and look a bit like a cigar. I find some every year in my garden and I am quick to feed them to the chickens!
What Damage Do Tomato & Tobacco Hornworms Cause?
The Tomato Hornworm causes complete and utter destruction. It will strip leaves overnight off any nightshade plant. An infestation can defoliate entire rows killing the plants.
Companion Plants to Help with Hornworms
Companion plants are always good to have in the garden to help deter harmful pests and attract good ones.
Dill, basil and marigolds are excellent companion plants for hornworm deterrent to help hide tomato plants from eggs being laid. That said, I have these plants around my tomato plants every year and I still get hornworms.
Using Trap Crops for Hornworms
Tomato hornworms see everything as their favorite food. If you want to try a trap crop, you could plant a tomato you have no interest in along the edges of the garden in the hopes that the moths will lay their eggs on the trap crop. Honestly, as in life, there’s no guarantee that will actually happen.
How To Kill Tobacco or Tomato Hornworms
Hand Picking Hornworms
Hand picking the hornworms and dropping them into soapy water is the fastest treatment. If you see any eggs – squash them with or without gloves on, or remove the leaves you see the eggs hatching on.
Personally, I don’t like to touch hornworms, so I break/cut the leaf off and drop it into a pail of soapy water or save them for my chickens.
Hornworms hide very well among the leaves so it is always easier to spray the leaves with a foliar spray or water first. They’ll start to move around making it easier to find and hand pick them.
Handpicking hornworms is my best tip for killing these vile creations. I take sick delight in watching my chickens fight over them!
Using UV Lights to Find Hornworms
A lot of people have mentioned using UV flashlights to find hornworms at night – apparently they glow! I’ve never tried this because UV lights used to be quite expensive.
Now that they’re affordable I might give it a shot! But honestly, with slow diligence, it’s not hard to find hornworms during the day.
One way to more easily find hornworms is to look for their poop. This green / black pellet poop is quite large and obvious. When you see it, you know there’s a hornworm nearby.
bT Spray for Hornworms
Spraying the leaves and soil with Bt Spray as soon as you notice the caterpillars is also a good bet at beating them.
Use Bt and spray the leaves and soil and help kill the hornworms off. BT (Bacillus Thuringiensis) is a bacteria that infects and kills caterpillars. It’s approved for organic gardening and I use it primarily to kill cabbage worms when they get out of control on my brassicas.
Bt spray is quick to handle caterpillar issues as the bacteria keeps on going. An added benefit is it is nontoxic to mammals and bees. However, Bt WILL kill ALL caterpillars (including Monarchs) so be careful when spraying it. If you have the space you can support monarchs by creating a safe space for them far away from any overspray.
Following packaging directions, I mix a small amount into a spray bottle and spray it on leaves. You can also syringe some up and stick it directly into any spots that show where one has bored into your plants.
Soapy Water Spray
You can also mix up your own soapy water spray. Add a bit of cayenne pepper to really make those caterpillars die.
Using Diatomaceous Earth to Kill Hornworms
If you want to use DE to kill pests, you’ll need the food grade version. Food Grade Diatomaceous Earth is helpful for a lot of pests. It’s nontoxic and works best in dry conditions.
To use DE to kill hornworms, sprinkle the DE around the plant – keep it out of blooms if possible. When the hornwoms walk through it, it will enter their body and start to dry them out.
DE has pros and cons. The pros are it’s effective at killing bugs. The cons are – it can harm bees. Another con is that you really need to wear a dust mask when applying it to keep your lungs safe.
How To Break The Lifecycle of The Tomato Hornworm
Not only is know how to kill tomato hornworms important, but figuring out how to break the lifecycle so you can prevent them in the future is also helpful. Here are a few things you can try to break the hornworm life cycle so they leave your garden alone.
Drench the soil with nematodes to kill the pupating larvae during summer or the overwintering pupa. As it enters the soil will attack and kill them to prevent them from coming back out. I have been using beneficial nematodes in my garden for a couple years now and am seeing good results with them.
A good garden practice is to rotate crops to help keep pests at bay. A good recommendation is that you should only plant the same crops in the same area once every three years.
That said, I don’t usually follow this guidance because I let volunteers grow. Feeding with good compost helps replenish nutrients when crops are regrown in an area.
However, rotating crops helps disrupt pest life cycle by interrupting their food supply. A good rotation for tomatoes is to plant nitrogen fixing beans there the next year.
Tilling the Soil
If you had a huge infestation last year, you can try tilling the soil. It has been shown to kill the overwintering pupae. I don’t really like to till my soil so I haven’t tried this myself.
How To Control Hornworms In The Future
Attract beneficial insects to help control hornworms in your vegetable garden. Beneficial insects include:
- Parasitic wasps
- Green lacewings
Plant a beneficial nursery of flowers and herbs that beneficial insects like to ehlp attract them to your garden.
Parasitic wasps are really cool. They lay eggs under the skin of the hornworms where the wasps consume the hornworm from the inside out.
Parasitic wasps are crazy to watch – I almost feel sorry for hornworms when I see them infected with parasitic wasps. Almost. LOL
Remember never kill the hornworm with white cocoons on it! You want these wasps to hatch and lay more eggs on more hornworms.
And that’s what I know about how to kill tomato hornworms! Gardening means we’re always learning and trying new things! Including learning how to effectively deal with pests.
Have you had Tomato Hornworms in your garden? How do you deal with them?