11 Ways To Prevent & Control Tomato Hornworms This Season
Have you experienced tomato hornworms taking over your garden? It's not a fun experience! Luckily there are many different ways you can prevent this from happening. In this article, gardening expert Merideth Corhs walks through her favorite ways to prevent and control tomato hornworms in your garden this season.
Tomato hornworms have to be one of my least favorite tomato pests of all time. Don’t get me wrong… I hate aphids, spider mites, beetles, and stink bugs too, but hornworms really gross me out. They cause huge amounts of damage in very short amounts of time, they’re difficult to see, and they love to eat many of the veggies I love to plant.
So, we know that hornworms are a big threat to our gardens. What can we do about them? In this article, you’ll learn all about tomato hornworms. You’ll also learn 11 different ways you can prevent them from becoming a problem in your garden.
Tomato Hornworms: What Are They?
Tomato hornworms are truly unforgettable tomato pests. They’re big, green, and their long horn gives them a sinister aura. Beyond their distinct look, hornworms are possibly the most destructive tomato pest there is.
These large caterpillars will eat non stop and can quickly defoliate an entire tomato (or peppers, eggplant, and potatoes) plant. They are very well camouflaged against the leaves and stems and can be quite hard to see while still small.
A telltale sign that you’re dealing with a hornworm is seeing a branch or portion of a branch with no leaves in the morning. As they get larger, hornworms are easier to see, but they will have already done quite a bit of damage. Carefully look along stems, lifting leaves to find the hornworms underneath.
Tomato hornworms are incredibly destructive and are very common throughout North America and Australia. The hornworm is the caterpillar of the five-spotted hawkmoth, but don’t confuse this with other butterfly/moth species you want to help propagate. They don’t need the help…
Once you know what you’re looking for, you’ll find the tomato hornworm fairly easy to spot.
Mature caterpillars can grow to between 3-5 inches long and have a long black or brown horn sticking out of their rear. The body has v-shaped white markings with rows of white and black spots.
After the caterpillars have eaten their fill – often the foliage of your ENTIRE plant – the hornworm will burrow into the soil. Resulting pupae are large (3-4 inches) and reddish-brown. Pupae can overwinter in the soil if it’s late enough in the season, which makes them a very long-lasting threat.
The final stage of their life cycle is a large gray moth known as the five-spotted hawk moth. Moths will emerge from the soil in the summer and go on to lay as many as 2000 eggs on the undersides of leaves.
They do this mainly at night so their activity is difficult to see. You can find eggs the next day and scrape them off. Eggs appear light green or white and appear in clusters.
11 Ways of Prevention & Control
Control and prevention of the tomato hornworm often require a multi-pronged approach. Manual removal paired with practical gardening practices is often the most effective methodology. But if you’re dealing with a major infestation, there are several OMRI-approved chemical options you can use.
The best way to get rid of hornworms is to pick them off by hand. I hate hornworms and am a little squeamish around them. If you’re anything like me, plan to use gloves while handling them.
The caterpillar will wiggle and attach itself strongly to the stem they’re on. If you’re lucky enough to have chickens, they love eating hornworms. Otherwise, you can squish them or put them in a jar of soapy water.
Hornworms are notoriously difficult to see, especially when they’re small. You’ll need to look at every stem and branch to see if there are caterpillars about.
I recently saw a gardening friend use a blacklight at night in her garden. I’m still not sure why this is, but those hornworms stand out brilliantly under a black light. You’ll have a little homing beacon for every one of them! If you’re dealing with a lot of these pests, this is a great way to easily find them.
Tomato hornworms are native to North America and in a healthy ecosystem, they are kept in check by natural predators. This includes bugs like ladybugs and lacewings – which eat eggs and young larvae – as well as parasitic wasps.
So far, there is no real evidence that companion planting your tomatoes with a particular flower, herb, or veggie has any effect on deterring hornworms on its own. With that said, there are a number of plants that attract the kind of predatory insects we just referenced.
You can invite predatory insects into your garden naturally through purposeful companion planting, or purchase them for release into your garden.
Just remember that if you do release predatory insects into your garden, you’ll want to have their preferred flowers and herbs around to keep them there. Otherwise, your purchased insects will fly off to more accommodating locations.
Wasps often bring to mind large, predatory paper wasps. While those prey on hornworms as well, a tiny parasitic wasp called trichogramma may pose an even better opportunity for pest control.
Rather than killing a hornworm outright, female trichogramma wasps inject them with eggs and fly away. Eggs soon release little wasp larvae, which feed on the hornworm until they’re ready to pupate. These larvae are very visible to us and look a bit bizarre.
At this stage, the hornworm is still alive and walking around, but it will have stopped eating. If you happen to see a hornworm in this state, leave it alone and let the new wasps hatch and spread in your garden.
Trichogramma wasps are quite effective at stopping an infestation in its tracks before too much damage is done. The best plants to attract and support these wasps are buckwheat and sweet alyssums.
Ladybugs and lacewings can also help you control tomato hornworm populations by munching on eggs and larvae. There are quite a few plants that attract these beneficial insects. Try planting sweet alyssum, butterfly weed, garlic, marigolds, calendula, queen anne’s lace, parsley, cilantro, or dill.
As we mentioned earlier in this article, tomato hornworms overwinter in the soil as reddish-brown pupae. They emerge in the following summer as moths who will then lay eggs on your tomato plant. Once those eggs hatch into caterpillars, the destructive process begins all over again.
If you can interrupt this overwintering stage, you can help prevent adult moths from emerging the next year.
One of the most effective ways of doing this is by tilling the soil both at the beginning and end of the gardening season. This will bury lingering hornworm pupae (and other overwintering pests) deep within the soil, preventing them from emerging as moths.
In fact, if you see these rather gross looking pupae in your soil, pick them out and destroy them immediately.
Mulch is incredibly important in your garden but is often overlooked or skipped altogether. Mulch provides protection against excessive heat, aids with moisture retention in the soil, prevents water splash back (which can spread fungal diseases from the soil), and discourages weeds.
Beyond these key benefits, a thick layer of mulch can also prevent the adult moth from emerging from the soil and laying eggs on your tomato plants. The more layers of dirt and mulch you put in between those larvae and your plants the better!
You can use a lot of things as mulch including organic material you may have laying around in your yard. Straw, wood chips, crushed leaves, and even crushed eggshells can offer the soil that extra layer of protection.
Your local nursery or garden center will also have plenty of mulch options available. I personally love using coconut coir, which is sustainably produced and great for your garden. But no matter the type of mulch you choose, aim to apply a layer 2-3” thick for maximum benefit.
If you know you’re dealing with repeat issues with overwintering pests like the tomato hornworm, using black plastic in your garden may be a great option. Black plastic is often used by gardeners who live in a cooler climate and want to keep soil temperatures nice and warm for their plants.
In this case, black plastic acts as a solid barrier that prevents adult moths from surfacing. This will cause the moths to die below the surface of the soil and save your tomatoes from their destruction.
Floating row covers can also be a great tool when it comes to pest prevention. Pests cannot eat and infest your plants if they cannot find them! If you have chosen to plant determinate – or bushing – tomatoes this season this may be an option for you.
You’ll have a much more difficult time using a row cover for sprawling indeterminate varieties.
If you do choose to use row covers, remember that you’ll have to help your plants out with pollination. Tomato and pepper plants will need a little shake if they’re not experiencing natural wind.
While row covers will prevent moths from laying eggs on your plants, they won’t prevent overwintering moths from emerging from the soil underneath the row covers. So if you do choose this option, be sure to pair it with other options like tilling and mulching.
Crop rotation is always a good idea when it comes to vegetables in the nightshade family. Certain diseases and pests like to attack these plants year after year.
If you plant them in a different area of your garden, they won’t be susceptible to those issues. It’s a good idea to leave 1-3 years in between plantings if your space supports this.
Before resorting to chemical – even organic options – solutions, you may want to try some homemade cayenne pepper spray. This is one of those solutions that floats around gardening groups because it can be very effective. The only caveat is that you need to reapply fairly often since rain will wash it off and wind will dry it out quickly.
This works pretty well because the capsaicin in the cayenne pepper repels the hornworms (and a lot of other pests as well). You can spray leaves, branches, and the ground with the solution.
One of my favorite recipes uses fresh hot peppers like habaneros along with cayenne pepper for an extra powerful punch. This gets mixed with garlic, dish soap, and water. When making something like this be sure to wear gloves so you don’t inadvertently wipe your eyes with peppery fingers!
Neem is an excellent tool for any organic gardener to have close at hand. Neem acts as a natural insecticide for many pests that plague tomatoes including aphids, whiteflies, and hornworms.
Neem oil creates a light coating on the leaves and stems of your tomato plant. This can stop new eggs from hatching and also makes the leaves less appealing to eat. If the oil is sprayed on the bugs themselves, it can suffocate them.
You do need to be cautious when spraying neem oil since it can kill beneficial insects as well. We recommend using this sparingly and only if other methods are failing you. Especially if you’ve worked hard to introduce good bugs into your space, you don’t want to create a hostile environment for them.
If you’re dealing with a really bad infestation of tomato hornworms and the other methods we’ve discussed just aren’t cutting it, you may need to turn to a harsher control method. Botanical BT is a good option in this case.
Bt (Bacillus thuringiensis) is a natural bacteria often found in the soil. Just like with Neem oil, Bt will coat the leaves and branches of your tomato plant. When hornworms eat the leaves, the Bt paralyzes their digestive system and will cause them to die. Unlike Neem, Bt won’t bother pollinators.
Different strains of Bt work on different kinds of pests. For tomato hornworms, look for Bt kurstaki. Always look for an OMRI-certified product.
Diatomaceous earth is a natural substance made of microscopic aquatic organisms. When seen up close, it looks a lot like broken glass. In addition to desiccating hornworms (drying them out), the small sharp bits also damage the soft undersides of the caterpillars. This solution is most effective when dealing with younger hornworms.
DE can be equally as harmful to beneficial insects and pollinators, so be judicious in its use.
When it comes to trying to control or prevent a pest like tomato hornworms, your best bet is to use as many control methods as possible. This kind of integrated pest management approach will ensure you have the best chance in protecting your prized veggies this season. Happy planting!