Dealing with Tomato Hornworms in a Hydroponic System

What Tomato Hornworms Do

Tomato hornworms are the large green caterpillar larvae of hawkmoths that voraciously eat foliage and fruit of tomato plants. They can strip a plant of leaves quickly, leaving behind dark droppings and reducing yield. [1]

Latin Name

Manduca quinquemaculata [1]

Identification

Up to 8 cm long, bright green caterpillars with white V-shaped marks on each side
Prominent black horn on the posterior segment
Coarse body hairs and smooth skin
Large green or black droppings on leaves and trays [2]

Alternative Names

Five-spotted hawkmoth caterpillar
Tomato worm
Hawkmoth larva

Varieties (Related Species)

Manduca quinquemaculata (tomato hornworm) [1]
Manduca sexta (tobacco hornworm) [1]

Climates Where They Thrive

Warm temperate zones (15-30 °C) with moderate humidity [2]
Population declines above 32 °C or below 10 °C
Tolerant of greenhouse conditions but avoid hot, arid extremes

Companion Planting as Deterrents

Cultivar	Hydroponic Methods	Effectiveness
Basil (Ocimum basilicum)	NFT, DWC, Drip	Moderate-aromatic oils mask tomato cues [3]
Marigold (Tagetes spp.)	All methods	Moderate-thiophene compounds repel adults [3]
Borage (Borago officinalis)	Drip, Ebb & Flow	High-attracts beneficial predators [3]
Chives (Allium schoenoprasum)	All methods	High-sulfur volatiles deter moths [8]

Natural Predators

Braconid wasp (Cotesia congregata)-parasitizes caterpillars [6]
Egg parasitoids (Trichogramma spp.)-attack eggs [7]
Ladybird beetles (Coccinellidae)-eat eggs and small larvae [2]
Green lacewing larvae (Chrysopidae)-consume young caterpillars [2]
Paper wasps (Polistes spp.)-hunt large larvae [2]

Remedies

Treatment	Hold Period	Natural?	Effectiveness
Hand-picking nocturnal larvae	0 days	Yes	High-immediate removal [2]
Bacillus thuringiensis (Bt) spray	0 days	Yes	High-ingested larval toxin [4]
Spinosad formulations	3 days	No	High-effective on young larvae [5]
Insecticidal soap spray	1 day	Yes	Moderate-contact kill of small larvae [5]
Sticky barrier collars	0 days	Yes	Low-prevents small larvae from climbing [2]

Other Remedies

UV-blacklight scouting: Use UV LED at night to find glowing larvae [1]
Reflective mulch: Line trays with foil to disorient moths [3]
Essential oil diffusion: Disperse lemongrass or peppermint oil vapor
Acoustic deterrence: Low-frequency sound pulses to disrupt feeding

Tips and Tricks

Inspect plants under UV or torchlight at dusk and dawn
Quarantine new seedlings under fine mesh for 7-10 days
Rotate treatments weekly to prevent resistance buildup
Maintain strong airflow to reduce moth egg‐laying
Sanitize net pots and trays between crops

Common Hosts

Tomatoes (Solanum lycopersicum)
Eggplants (Solanum melongena)
Peppers (Capsicum spp.)
Tobacco (Nicotiana spp.)
Potatoes (Solanum tuberosum) [1]

Citations

[1] Manduca quinquemaculata - Wikipedia - https://en.wikipedia.org/wiki/Manduca_quinquemaculata
[2] Tomato hornworms in home gardens - UMN Extension - https://extension.umn.edu/yard-and-garden-insects/tomato-hornworms
[3] Tomato Hornworm Control - Planet Natural - https://www.planetnatural.com/pest-problem-solver/garden-pests/tomato-hornworm-control/
[4] Hornworms on Tomatoes - UNH Extension - https://extension.unh.edu/resource/hornworms-tomatoes-new-hampshire-fact-sheet-0
[5] How to Identify and Get Rid of Tomato Hornworms - Farmer's Almanac - https://www.almanac.com/pest/tomato-hornworms
[6] Cotesia congregata - Wikipedia - https://en.wikipedia.org/wiki/Cotesia_congregata
[7] Trichogramma - Wikipedia - https://en.wikipedia.org/wiki/Trichogramma
[8] Hornworms on Tomatoes - Wisconsin Vegetable Entomology - https://vegento.russell.wisc.edu/pests/hornworms/