There are few experiences that are as joyfully delicious as biting into a warm, juicy, summer sun-warmed tomato fresh off the fine. In contrast, that experience can swiftly become horrifying if the fruit you’ve just bitten into is full of worms.
Let’s take a look at tomato pinworms, and how to prevent them from obliterating your nightshade plants.
What are Tomato Pinworms?
Tomato pinworms are the larvae of tiny little gray Keiferia lycopersicella moths. These are normally limited to warmer regions in the southern USA and the Caribbean, but most recently, they’ve been found as far north as Pennsylvania and Delaware.
These pinworms aren’t limited to outdoor crops: they’ve been found in greenhouse-grown plants as well!
Although they’re normally associated with tomatoes, these pinworms can affect any nightshade (Solanaceae) plants, such as potatoes, sweet peppers, and eggplants.
The pupae lie dormant in soil during the winter, and emerge in springtime to lay their eggs in small groups of two or three on the undersides of host plant leaves. When the tiny larvae emerge, they spin tiny little silk tents for themselves as supportive protection as they tunnel into the leaves to eat.
From there, they move onto the fruits and cause significant damage to what should be a delicious crop you’re looking forward to harvesting. This is especially true because tomato pinworms can create up to ten generations in a single growing season.
Identifying Tomato Pinworms
Early pinworm activity is often misidentified as leafminer presence because their effects on tomato and other nightshade leaves are quite similar.
The newly hatched larvae are only a few millimeters long, and they’ll burrow into leaf tissue and eat as they go. This leaves long, discolored trails behind them—much like leafminer damage.
As they get older, however, they shift their attention towards the stems and fruit. They’ll bore holes into the stems, rendering the plant vulnerable to various pathogens, and make similar holes into the developing fruits.
The pinworms will then crawl inside said fruits and make comfortable little homes for themselves, eating all of the flesh around them as they plump up and prep themselves to pupate.
Things can get worse (and holes get much bigger) if birds realize that there are worms in your tomatoes. They’re particularly fond of pinworms and will peck great holes in the developing fruits to try and get at the larvae within.
As a result, not only will you have worm damage in your crop, but your healthy, unaffected tomatoes may be torn apart by zealous larvae feasters.
If you see holes on your tomato or eggplant fruits, surrounded by discolored flesh, you’re likely dealing with pinworms. You can check by slicing the fruits open and checking for them. If you see small, gray-brown larvae with dark stripes inside, this will confirm your suspicions.
Should the damage you’re seeing turn out to not be pinworms, our article on How To Identify and Stop Tomato Pests in Their Tracks can help you determine what’s causing it.
How to Eliminate Tomato Pinworms
These larvae are quite insidious, and can cause a heck of a lot of damage.
When and if you confirm that you’re dealing with tomato pinworms, it’s important to deal with them as swiftly as possible. Otherwise, you may see damage in 60-80% of your fruits in a single growing season. [1]
One of the best ways to reduce tomato pinworms in your crops is with integrated pest management.
For example, covering your tomato plants with floating row covers reduces the possibility of the mature moths laying their eggs on the leaves. In addition to (or in lieu of) using these covers, take a flashlight outside at dusk (or shortly after nightfall) to check your plants.
This is when pinworms are most active, and you should be able to pick off several of them and either drown them in soapy water, or save them to feed to your chickens. Then, be sure to rotate your crops next season so you don’t grow other nightshades there for three years.
Although some growers use Bacillus thuringiensis or spinosad to control caterpillar infestations, these aren’t terribly effective with tomato pinworms, which have proven themselves to be resistant to common insecticides. [2] One of your best options to control and prevent pinworms in the future is with diligent management.
Note that if you do use insecticides, don’t feed the worms to your poultry.
If you find any pinworm activity, remove the affected plants and either bury them at least a foot deep to prevent remaining pupae from emerging back up to the soil’s surface or burn them. Inspect plants daily, and pay close attention to any brown or shriveled leaves.
At the end of the growing season, eliminate and destroy garden debris, and turn the soil to a depth of at least six inches. This should either bury pupae that are cozying up to overwinter, or expose them for bird predation.
Then be sure to plant a different crop in that area next year: any remaining pupae will be thwarted by a lack of appropriate food options and die off before they can continue their life cycle.
Additional Notes on Avoiding Tomato Pinworms
If, after trying different growing and management techniques, you still face issues with tomato pinworms, then you can try some alternative growing methods.
For example, instead of growing your tomatoes in soil, you can set up hydroponic bays for them instead. Since the pinworms live in soil and drown easily in water, they won’t be able to get close enough to your plants to damage them.
Furthermore, if you’re growing inside a greenhouse or other building, it’s unlikely that the adult moths will be able to get to them to lay eggs on their foliage.
Another option is to grow your plants upside-down in hanging planters. As long as you use sterilized soil that’s unlikely to have pupae in it, there will be significantly less risk of larvae damage.
Letting your chickens, turkeys, or Guinea fowl roam through your nightshade plants is a great way to reduce both tomato pinworms, and other caterpillar species that like to feast upon them. As mentioned, however, don’t let them eat these wigglers if you use any kind of pesticide, as they can harm your birds irreparably.
Learn more about which common insects are safe for your birds in our article 14 Bothersome Garden Insect Pests Chickens Can Eat.
As a final note, don’t freak out too much if you bite into a tomato and find one-half of a worm in there. Although it may nauseate you to realize that you’ve consumed more protein than intended with that bite, these worms are completely harmless if ingested by humans.
References:
- Elmore JC, Howland AF. 1943. Life history and control of the tomato pinworm. USDA Technical Bulletin 841. 30 pp.
- Guedes, Raul Narciso & Roditakis, Emmanouil & Ribeiro de Campos, Mateus & Haddi, Khalid & Bielza, Pablo & Siqueira, Herbert & Tsagkarakou, Anastasia & Vontas, John & Nauen, Ralf. (2019). Insecticide resistance in the tomato pinworm Tuta absoluta: patterns, spread, mechanisms, management and outlook. Journal of Pest Science. 92. 3. 10.1007/s10340-019-01086-9.
