Tomato hornworms are the larval stage of the sphinx moth and can cause significant damage to tomato plants in a garden. The adult moths lay their eggs on the underside of leaves, which hatch into the larval stage of the tomato hornworm. These caterpillars feed on the foliage and fruit of the tomato plant, causing significant damage. They can defoliate entire plants in a matter of days and can significantly reduce the yield of a garden.
Tomato hornworms are most active during the summer months, when temperatures are warm and the plants are in full growth. In a single season, a single tomato hornworm can consume an entire plant, leaving only the stem and roots. The caterpillars can be difficult to control, as they are well-camouflaged and blend in with the foliage of the plant.
Symptoms
- Large, irregular holes in leaves and fruit: Tomato hornworms are notorious for their voracious appetite and can quickly defoliate plants by eating large holes in the leaves and fruit.
- Stripped branches and stems: As the caterpillars grow, they may also strip the branches and stems of leaves, leaving the plant looking bare.
- Presence of frass (insect excrement) on the ground or on leaves: Tomato hornworms produce large amounts of frass, which can be found on the ground or on leaves near the infested plant.
- Yellowing and wilting of leaves: As the caterpillars continue to feed, they may also cause the leaves to yellow and wilt, which can weaken the plant and reduce its yield.
- Presence of large, green caterpillars up to 4 inches long: The caterpillars themselves are large, green, and can reach up to 4 inches in length. They are easily visible and can be found on the leaves and fruit of the infested plant.
- Stunted plant growth: Tomato hornworms can cause stunted growth in plants, reducing the overall size and yield of the garden.
What is a Tomato Hornworm
Larvae
- Green body with white stripes and black markings: Tomato hornworms have a green body with white stripes running vertically along the length of their body. They also have black markings on their sides that resemble eyes, which are thought to deter predators.
- Approximately 4 inches long: Tomato hornworms can grow up to 4 inches in length, making them one of the largest caterpillars in North America.
- Horn-like protrusion at the rear end: The caterpillars have a distinctive horn-like protrusion at their rear end, which is where they get their name.
- Possess large, triangular “saddle” markings on their back: The caterpillars also have large, triangular markings on their back that resemble saddles. These markings are unique to each individual caterpillar and can be used to identify different species.
- Fat and cylindrical body shape: Tomato hornworms have a fat, cylindrical body shape and can be found on the leaves and fruit of the infested plant. They are easy to spot and can cause significant damage if not controlled.
Adult
- Wingspan: The wingspan of the adult tomato hornworm can reach up to 5 inches.
- Color: The adult tomato hornworm is a large, dark-colored moth.
- Wings: The wings are large and broad, with distinct patterns and markings.
- Body: The body of the adult tomato hornworm is plump and compact, with a robust thorax and a narrow waist.
- Head: The head is small and has large, compound eyes and antennae.
- Legs: The legs are thin and spindly, and are used for perching and grasping.
- Mouthparts: The mouthparts are long and slender, and are used for feeding on nectar from flowers.
Treating a Tomato Hornworm Infestation
It may be necessary to use multiple methods to effectively control tomato hornworms in a garden. For example, using sticky bands to trap the caterpillars, along with hand-picking, can help reduce the population.
Physical Control Methods
Hand-picking
- Timing: Best done in the early morning or late evening, when the caterpillars are less active and easier to spot.
- Technique: Carefully inspect the plants and pick off any caterpillars that are present. Dispose of the caterpillars in a bucket of soapy water to kill them.
- Advantages: This method is safe, effective, and environmentally friendly.
- Limitations: It can be time-consuming and labor-intensive, especially in large gardens or when the infestation is heavy.
Row covers
- Material: Row covers can be made from a variety of materials, including lightweight garden fabric, spun-bonded polyester, or floating row covers.
- Installation: Place the row covers over the young tomato plants before the moths lay their eggs and remove them when the plants start to flower, to allow for pollination.
- Advantages: This method is easy to implement and can provide complete protection for the plants.
- Limitations: It may be difficult to remove and replace the covers, especially in windy conditions, and the covers must be removed to allow for pollination.
Sticky bands
- Material: Sticky bands can be made from a variety of materials, including double-sided sticky tape, Tanglefoot, or petroleum jelly.
- Installation: Place the sticky bands around the trunk of the plant, at the base of the stem, to trap the caterpillars as they climb up and down the plant.
- Maintenance: Check the bands regularly and remove any trapped caterpillars. Dispose of the caterpillars in a bucket of soapy water to kill them.
- Advantages: This method is easy to implement and can be very effective in reducing the population of caterpillars.
- Limitations: The bands may need to be replaced frequently, especially in wet or humid conditions, and they may trap beneficial insects, such as ladybugs or lacewings.
Cultural Control Methods
Crop rotation
- Technique: Plant tomatoes in a different area of the garden each year to break the life cycle of the pest.
- Advantages: This method is easy to implement and can help reduce the number of tomato hornworms in the garden over time.
- Limitations: This method is most effective when used in combination with other control methods, as it does not provide immediate control of the infestation.
Clean up
- Technique: Remove any damaged or diseased plants, as well as any fallen leaves, from the garden to reduce the number of places where the moths can lay their eggs.
- Advantages: This method is easy to implement and can help reduce the population of tomato hornworms in the garden.
- Limitations: This method should be done regularly, as fallen leaves and plant debris can accumulate quickly.
Chemical Control Methods
Insecticidal soap
- Application: Apply the soap directly to the caterpillar and the affected leaves.
- Timing: Reapply the soap every 7 to 10 days, or as needed, to keep the caterpillars under control.
- Advantages: This method is safe for use in a vegetable garden and is effective in controlling tomato hornworms.
- Limitations: The soap can be washed off by rain or irrigation and may need to be reapplied regularly.
Neem oil
- Application: Apply the oil directly to the caterpillar and the affected leaves.
- Timing: Reapply the oil every 7 to 10 days, or as needed, to keep the caterpillars under control.
- Advantages: This method is safe for use in a vegetable garden and is effective in controlling tomato hornworms.
- Limitations: The oil can be washed off by rain or irrigation and may need to be reapplied regularly.
Biological Control Methods
Beneficial insects
- Types: Ladybugs and lacewings are two examples of beneficial insects that can be introduced into the garden to feed on the caterpillars.
- Introduction: Order the beneficial insects from a reputable supplier and release them into the garden according to the supplier’s instructions.
- Timing: Release the beneficial insects when the tomato hornworms are present, or just before they are expected to arrive.
- Advantages: This method is environmentally friendly and can help control the infestation without the use of chemicals.
- Limitations: This method may not be able to control a heavy infestation on its own, and may need to be used in combination with other control methods.