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Keep an Eye Out for Tomato Hornworm

Posted: July 28, 2015

Tomato hornworms on your tomato plants can be a problem from July through early September in Pennsylvania. This pest is not a big problem and for that reason it can be overlooked; however if populations explode you can rapidly 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.

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

Hornworm defoliation damage

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

Late instar larvae also feed on fruit leaving large areas with feeding damage.

Hornworm feeding damage

Another sign of tomato hornworm presence is their frass, which is large and resembles rabbit droppings. Frass can be found on leaves and also on the ground or plastic mulch.

hornworm frass

Management options

Tilling in the spring and fall can expose pupae to wind, weather and predators. Rotating to crops that are not hosts to tomato hornworm can help in management. Managing solanaceous weeds eliminates  hosts for tomato hornworms. Handpicking them from plants and destroying them can be effective in small areas, however be careful to leave any that are parasitized (see photo below).

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 tomato hornworm. Wasps lay their eggs on the larvae. When the eggs hatch, larvae feed on the insides of the hornworm and then pupate. White cocoons appear on the outside of the hornworm body. Wasp cocoons are easily found on parasitized hornworms. When the wasps emerge, the hornworm will die and adult wasps will seek out other hornworms to repeat the cycle.

parasitized hornworm

When more than one hornworm larvae is found per 10 plants in affected areas of the field, chemical control may be warranted. There are several materials that are effective a killing tomato hornworm. 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 Integrated Pest Management with an Emphasis on Biocontrol manual (available for purchase). The products in parenthesis are OMRI approved, but if you are an organic farmer check with your certifier to make sure that they can still be used.

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

The following options are from the 2015 Commercial Vegetable Production Recommendations guide. Apply one of the following formulations:

  • Bacillus thuringiensis --1.0 to 2.0 lb Dipel (or OLF)
  • beta-cyfluthrin--1.6 to 2.8 fl oz/A Baythroid XL (or other labelled mixtures containing beta cyfluthrin like Leverage 360)
  • bifenthrin--2.1 to 5.2 fl oz/A Bifenture (Sniper, or OLF)
  • chlorantraniliprole--soil/drip/foliar 3.5 to 5.0 fl oz/A Coragen 1.67SC (or other labelled mixtures containing chlorantraniliprole like Durivo and Voliam flexi)
  • cyantraniliprole--soil 5.0 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 labelled 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 labelled 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

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Article Details

Title

Keep an Eye Out for Tomato Hornworm

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Contact Information

Elsa Sánchez
  • Associate Professor of Horticultural Systems Management
Email:
Phone: 814-863-2433
Katie Ayers
  • Penn State Plant Science