Keep an Eye Out for Hornworms

Generally, this pest is not a big problem, so it can be overlooked. If populations explode, you can see a lot of damage to the plants and fruit.

Signs and symptoms in the field

Here in the center of the state, we started noticing single lime green, small (approximately 1/10 cm), shiny eggs on the top or bottom surface of leaves of tomato, pepper, and other solanaceous crops in early July (Figure 1.).

Larvae hatch from the eggs about 6–8 days later and begin feeding on tomato leaves targeting new growth. Larvae go through 5 instar stages, with the final stage resulting in the majority (about 90%) of all of the feeding damage.

Figure 2. Photo: Elsa Sanchez, Penn State

Upper portions of the plant can become defoliated, with the mid-rib being left behind (Figure 2.).

Late instar larvae also feed on fruit leaving large areas with feeding damage (Figure 3.).

Figure 3. Photo: Elsa Sanchez, Penn State

Another sign of hornworm presence is their large frass, which resembles rabbit droppings. Frass can be found on leaves, the ground, or plastic mulch (Figure 4.).

Figure 4. Photo: Elsa Sanchez, Penn State

Management options

Tilling in the spring and fall can expose pupae to wind, weather, and predators. Rotating to crops that are not hosts to Hornworms can help in management. Managing solanaceous weeds so that Hornworms cannot use them as hosts. Handpicking them from plants and destroying them can be effective in small areas, but leave any that are parasitized (see Figure 5.).

Eggs and early instar stages are vulnerable to attack by lady beetles, minute pirate bugs, green lacewing larvae, parasitoid wasps, and spined soldier bugs (prey on larvae). Braconid wasps (Cotesia congregtus) are natural enemies of Hornworms. They lay their eggs on the Hornworm larvae. Eggs hatch, feed on the insides of the Hornworm, and then pupate. White cocoons appear on the outside of the Hornworm body.

Figure 5. Photo: Elsa Sanchez, Penn State

When more than one Hornworm larvae are found per 10 plants in affected areas of the field, chemical control may be warranted (Vegetable Integrated Pest Management with an Emphasis on Biocontrol).

Several materials are effective a killing Hornworms. The key to success is to apply them when larvae are less than ¾ inch long.

The following biorational options are from Penn State’s Vegetable IPM with an Emphasis on Biocontrol manual. The products in parenthesis are OMRI-approved, but if you are an organic farmer, check with your certifier to ensure they can still be used.

• Azadirachtin (Aza-Direct)
• Bacillus thuringiensis Kurstaki (Dipel, Javelin WG)
• Pyrethrins (PyGanic)
• Spinosad (Entrust)

The following options are from the Mid-Atlantic Commercial Vegetable Production Recommendations.

Apply one of the following formulations:

• Bacillus thuringiensis --0 to 2.0 lb Dipel (or OLF)
• beta-cyfluthrin--1.6 to 2.8 fl oz/A Baythroid XL (or other labeled mixtures containing beta-cyfluthrin like Leverage 360)
• bifenthrin--2.1 to 5.2 fl oz/A Bifenture (Sniper, or OLF)
• chlorantraniliprole--soil/drip/foliar 5 to 5.0 fl oz/A Coragen 1.67SC (or other labeled mixtures containing chlorantraniliprole like Durivo and Voliam flexi)
• cyantraniliprole--soil 0 to 10.0 fl. oz/A, 6.75 to 10.0 fl. oz/A (CL), 10 fl. oz/A (ECB) Verimark; foliar 7.0 to 13.5 fl. oz/A, 10.0 to 17.0 fl. oz/A
• cyfluthrin--1.6 to 2.8 fl oz/A Tombstone
• emamectin benzoate--2.4 to 4.8 oz/A Proclaim 5 SG
• esfenvalerate--5.8 to 9.6 fl oz/A Asana XL 2.9 to 5.8 fl. oz/A Asana XL
• fenpropathrin--10.67 fl oz/A Danitol 2.4EC
• flubendiamide--1.5 fl oz/A Belt SC (or other labeled mixtures containing flubendiamide like Vetica)
• gamma-cyhalothrin--2.56 to 3.84 fl oz/A Proaxis 1.92 to 3.2 fl. oz/A Proaxis
• indoxacarb--3.5 oz/A Avaunt 30WDG (or OLF)
• lambda-cyhalothrin--1.28 to 1.92 fl oz/A Warrior II or 2.56 to 3.84 fl oz/A Lambda-Cy (LambdaT, or OLF) (or other labeled mixtures containing lambda-cyhalothrin like Endigo ZC)
• lambda-cyhalothrin+chlorantraniliprole--6.0 to 9.0 fl oz/A Voliam Xpress
• methomyl--Lannate LV (see label for rates and current registration status)
• methoxyfenozide--4.0 to 8.0 fl oz/A (early season) or 8.0 to 16.0 fl. oz/A (late season) Intrepid 2F
• novaluron--9.0 to 12.0 fl. oz/A Rimon 0.83EC
• spinetoram--5.0 to 10.0 fl oz/A Radiant SC
• spinosad--3.0 to 6.0 fl oz/A Entrust SC
• tebufenozide--6.0 to 8.0 fl oz/A (early season) or 8.0 to 16.0 fl. oz (late season) Confirm 2F
• zeta-cypermethrin--2.24 to 4.00 fl oz/A Mustang Maxx (or OLF)
• zeta-cypermethrin+bifenthrin--4.0 to 10.3 fl oz/A Hero EC