If you’ve noticed little tunnels winding through your tomatoes and fruit that is rotting from the inside-out, you probably have an infestation of tomato fruitworms.
These annoying pests are also called corn earworms and cotton bollworms because they also attack many agricultural crops, including cotton, corn, tobacco, legumes, grains, fruits, and vegetables. They can pose a huge problem in your garden with their voracious appetite.
Fruitworms do the most damage in their larva form when they burrow and tunnel through tomato fruits.
They can eat the entire interior of a tomato and leave behind a cavity filled with nasty droppings, liquid, and rotten remnants of fruit.
The tomato will decay and fall off the vine, rendering it completely inedible. Removing damaged or infested fruit is the first step of any control plan, but to truly get rid of tomato fruitworms, you’ll have to go on the offensive.
Tomato fruitworms can destroy a small garden planting of tomatoes fairly quickly. Thankfully, you don’t need any scary chemicals to get rid of these annoying worms.
A fruitworm infestation can be dealt with by applying simple organic control methods like Bt, parasitic wasps, and diatomaceous earth.
If you notice a bunch of tunneled rotting tomatoes, don’t panic! Try a few of these methods to get rid of tomato fruitworms and save your tomato crop.
What are Tomato Fruitworms?
Tomato fruitworms go by the Latin name Helicoverpa zea. The pesky cream, yellow, green, or brown worms are actually the larvae of the Helicoverpa zea moth. These moths are native to North America and widely distributed throughout the continent except for in Alaska and northern Canada.
Fruitworms belong to the Lepidoptera, or moth classification. The family is called Noctuidae because the adults tend to be nocturnal.
The adult stage is a light yellow to olive colored moth with one dark spot on each wing. They lay eggs on your tomato plants and when they hatch, the cream or white colored larvae (fruitworm caterpillars) begin their feeding rampage.
Where do Tomato Fruitworms Come From?
Fruitworms are found throughout the United States and Canada, but they are most problematic in mild regions.
They cannot overwinter successfully in cold northern states, however they routinely migrate up into the north during the growing season.
Fruitworm moths can migrate up to 250 miles (400 km) in a single night if they catch a downwind breeze.
Whether it is an overwintering or immigrant population, these pesky worms will wreak havoc on farms and gardens if they are left unchecked.
What do Tomato Fruitworms Eat?
In your garden, you will most often find them feeding on those early ripening tomatoes you worked so hard to tend.
They also eat peppers, corn, melons, peas, potatoes, pumpkins, and many other veggies.
The first sign of fruitworms will most likely be damaged tomatoes. Fruitworms feed on leaves and stems, but they love fruit the most.
They usually start with the green tomatoes and continue eating as fruits ripen. Unfortunately, once fruitworms have started feeding on your tomatoes they are no longer edible. The best way to deal with them is by killing existing worms and trying to save newer fruits.
Tomato Fruitworm Damage on Plants
Fruitworms begin by creating a tunnel about as large as a pea, often from the stem-side of the tomato.
This entry hole usually turns black and begins to rot by the time you discover it. They proceed burrowing into the interior of the fruit,
hollowing it out and leaving behind nasty brown-dotted frass (caterpillar poop) along with a rotten watery mess.
The tunneling is usually the key giveaway of this pest. You may also see fruitworms clinging to the outside skins of a tomato and munching away on rotting the fruit as it hangs on the vine. Their feeding sites will quickly turn brown or blackish as the fruit decays.
On leaves, you will probably notice the fruitworm frass first. Brownish-greenish piles of dotted poop will rest on the leaves similar to a tomato hornworm infestation. Black holes may be evident as well.
Damage on peppers, melons, and other veggies will look similar. In corn, the fruitworm usually begins at the top of the corn silks and eats its way down the kernels, leaving behind a gross lighter colored frass. Fungal diseases commonly take hold after the fruitworm has done its damage.
How to Identify Tomato Fruitworms
Once you have noticed blackened spots, rotting fruit, and/or tunnels through your tomatoes, you can verify that it is a tomato fruitworm by finding the worm itself.
These caterpillars are creamy-white, yellow, green, or reddish-brown in color. They may have pale stripes or black spots. Their bodies are hairy and about 1.5 to 2 inches long.
Fruitworms prefer green tomatoes. Another key sign that you have tomato fruitworms in the garden is noticing one tomato ripening considerably earlier than the others. Check inside for a fruitworm!
Tomato Fruitworms vs. Hornworms
The main distinction between tomato fruitworms and tomato hornworms is the size and the presence of a horn.
Hornworms are much larger (up to 4 inches long) and have a distinctive “horn” or prick on the front of their bodies, making them a creepy alien-like look.
Hornworms also prefer to chomp on leaves and climb along stems. Fruitworms are smaller with no horn and more likely to be found burrowing tunnels into green tomatoes.
Life Cycle of Fruitworms
Because tomato fruitworms are moths, they have 4 distinct life stages and undergo a complete metamorphosis.
You usually only find them in the egg or larval stage because the adults are nocturnal.
The cycle begins with adult moths that emerge in the spring. They are yellowish-tan to brown-colored and have a single dark spot in the middle of each of their wings.
H. zea moths have a 1 to 1.5” wingspan. Quickly after emergence, they begin laying eggs on tomato leaves.
Tomato fruitworm eggs are cream-colored or pure white with a spherical shape that is slightly flattened on one side.
The eggs are only the size of a pinhead and laid singly (as opposed to in clusters) on the top or bottom of a leaf. The eggs get a reddish brown ring and darken in color just before the larvae hatch.
This is the lifecycle stage that gives us the most problems as gardeners. The larve are ugly-looking caterpillars with white, green, yellow, or reddish-brown bodies and stripes that run lengthwise along their backs.
They’re about 1.5 to 2” long and quite hairy. They have micro-spines that give them a rough feel when touched.
Up to four generations can reproduce in a single growing season, so it’s important to catch them early.
The larvae are greedy and cannibalistic; they’ll eat fellow fruitworms if they find them inside their tomato.
This is why you’ll typically only find one large worm feeding in each tomato. Most larvae will finish growing inside a single tomato (unless it is very small) and then fall to the soil to burrow and pupate.
The shiny brown pupa are the final life stage. They stay in this stage for 10 to 25 days in the summertime and emerge as moths to repeat the dreaded cycle.
At the end of the season, larvae will drop, pupate, and overwinter in the top 2-3 inches of soil.
This is why it’s important to thoroughly clear tomato debris at the end of the season and rotate tomatoes around different parts of your garden as a means of prevention.
How Do You Get Rid of Tomato Fruitworms?
Although damaged tomatoes cannot be saved, you can control fruitworms mid-season to stop them from taking out more fruit. Fortunately, there are lots of organic and biological control options.
Start by removing all fruitworm-damaged and rotting tomatoes. I usually throw them away instead of putting them in my compost pile, where they may continue their life cycle if not thoroughly heated and killed.
You can also prune and rake out any damaged leaves or stems to further sanitize the area. You don’t want any tomato debris on the ground for new emerging pupa to feed on.
2: Parasitic Wasps
Next, you can try releasing parasitic wasps. Don’t worry, they don’t harm humans in any way. These Trichogramma spp.
wasps are beneficial predatory insects that lay their eggs inside worms and caterpillars. When the eggs hatch, they eat tomato fruitworms from the inside-out like voracious zombies.
Parasitic wasps are the best kind of wasps to have in your garden because they are such effective biocontrol agents. They can also help control tomato hornworms, cabbage worms, and other pests.
You can purchase parasitic wasps from a biocontrol source and release them or you can practice “conservation biocontrol”, which is essentially just luring the wild wasps to hang out in your garden.
3: Diatomaceous Earth
You can also apply diatomaceous earth directly to the plant surface. The microscopically sharp particles of this white powder will pierce the skin of the fruitworm and dehydrate it.
Simply dust the powder over the leaves or develop fruit. While this is an organic control method, you should avoid inhaling the dust as it can be damaging to your lungs.
4: Apply Bt (Bacillus thuringiensis)
Bacillus thuringiensis is a soil bacteria that attacks caterpillars. This biological pesticide is completely organic and safe to use in your garden.
Bt is most effective in the warmest months when tomatoes are developing. It only targets caterpillars and will not harm beneficial insects like bees and parasitic wasps in your garden.
How to Prevent Tomato Fruitworm Damage
Once you’ve dealt with eliminating tomato fruitworms, you will probably want to prevent the headache in the future by taking some preventative steps to keep this pest at bay.
1: Conservation Biocontrol
As mentioned above, planting beneficial insectaries attracts beneficial predators like parasitic wasps.
This is the best proactive preventative method for maintaing a healthy thriving ecosystem that will keep fruitworms in check year-after-year.
To attract parasitic wasps throughout the growing season, you can plant insectary strips throughout your tomato beds.
The adult wasps will be attracted to feed on the nectar of these beneficial flowers and stick around to lay their parasitizing larvae.
Their favorite species include white alyssum, dill, parsley, asters, goldenrod, daisies, stinging nettle, yarrow, and Queen Anne’s lace flowers.
2: Minimize Local Food Sources
If possible, you should avoid planting corn, cotton, tobacco, or peppers near tomatoes because these are other hosts of the fruitworm.
This will help minimize other sources of food for the caterpillars and make it less likely that they will migrate to your tomatoes.
3: Crop Rotation
It is best to rotate tomatoes and other Solanaceae family crops around your garden so they aren’t grown in the same place year-after-year.
This is because those annoying little pupae will be waiting in the soil to hatch and lay eggs on the tomatoes in the same area.
4: Cover Tomato Plants
Excluding the moths altogether is also a very effective preventative strategy. You can use row cover or fine insect netting over your mature tomato plants to keep them safe from H. zea from the get-go. However, this method can be challenging if your tomato plants are very large.
If you are growing in a greenhouse or hoop house, you can simply close the sides before dusk to keep the moths from coming in and laying eggs.
Watching your delicious tomato fruits get eaten is frustrating and demoralizing. Fruitworms can get out of control very quickly and put a major dent in your tomato harvest.
Remember that prevention and ecological balance are key. Check your plants regularly, plant beneficial insectaries, and keep these pesky fruitworms out of your garden.
Amber Noyes was born and raised in a suburban California town, San Mateo. She holds a master’s degree in horticulture from the University of California as well as a BS in Biology from the University of San Francisco. With experience working on an organic farm, water conservation research, farmers’ markets, and plant nursery, she understands what makes plants thrive and how we can better understand the connection between microclimate and plant health. When she’s not on the land, Amber loves informing people of new ideas/things related to gardening, especially organic gardening, houseplants, and growing plants in a small space.