Dealing with Cutworms in a Hydroponic System
What Cutworms Do
Cutworms are caterpillar larvae of several noctuid moths that feed at night on young stems at the base, severing seedlings just above the growing medium and causing sudden plant collapse. [1]
Latin Name
Various Noctuidae larvae, notably Agrotis ipsilon (black cutworm), Agrotis segetum (turnip moth), and Peridroma saucia (variegated cutworm). [1]
Identification
- Plump, smooth-bodied caterpillars 25-40 mm long, gray-brown to greenish, often curled into a "C" shape when disturbed. [2]
- Seedlings or transplants suddenly cut off at soil/media line overnight.
- Larvae hide in debris or media surface during daylight. [1]
Alternative Names
- Strawberry cutworm
- Army cutworm
- Turnip moth larva
Varieties (Species)
- Agrotis ipsilon (Black cutworm) [1]
- Agrotis segetum (Turnip moth larva) [1]
- Peridroma saucia (Variegated cutworm) [1]
Climates Where They Thrive
- Temperate regions with mild winters; larvae overwinter as pupae and emerge in spring. [2]
- Inactive above 30 °C or below 10 °C; humidity less critical as they hide in substrate. [1]
Companion Planting as Deterrents
| Cultivar | Hydroponic Methods | Effectiveness |
|---|---|---|
| Onion (Allium cepa) | Drip, Ebb & Flow, DWC, NFT | High-sulfur volatiles repel larvae. [3] |
| Garlic (Allium sativum) | All methods | High-strong aroma deters oviposition. [3] |
| Marigold (Tagetes spp.) | All methods | Moderate-root exudates inhibit larvae. [4] |
| Spiny amaranth (Amaranthus spinosus) | All methods | Moderate-reported repellent in permaculture. [4] |
Natural Predators
- Ground beetles (Carabidae) that consume larvae. [2]
- Parasitic wasps (Trichogramma spp.) targeting eggs. [5]
- Beneficial nematodes (Steinernema carpocapsae) infecting larvae in media. [1]
Remedies
| Treatment | Hold Period | Natural? | Effectiveness |
|---|---|---|---|
| Hand‐picking nocturnal larvae | 0 days | Yes | High-immediate population reduction. [2] |
| Bacillus thuringiensis kurstaki (Bt‐k) spray | 0 days | Yes | High-ingested larval toxin. [1] |
| Beneficial nematodes (Steinernema carpocapsae) | 0 days | Yes | Moderate-infects larvae in media. [1] |
| Cardboard/foil stem collars | 0 days | Yes | Moderate-physical barrier at stem base. [5] |
| Diatomaceous earth top‐dress | 0 days | Yes | Low-abrades larval cuticle. [5] |
For chemical treatment, it is difficult to target them while they are buried underground. The best time to apply it is between midnight and dawn when they come out to feed. [2]
Other Remedies
- Nail collars: Insert short nails into collars around stems to prevent cutting. [5]
- Reflective mulch: Line trays with foil to disorient larvae emerging from media. [4]
- UV scouting: Use UV light at night to detect glowing larvae. [1]
- Essential oil diffusion: Disperse rosemary or thyme vapor to mask plant cues.
Tips and Tricks
- Inspect seedlings nightly under low light for cutworms. [2]
- Keep media surface clear of debris to reduce hiding spots. [1]
- Quarantine transplants before introducing to system. [1]
- Rotate control methods to prevent resistance. [2]
- Sanitize net pots and trays between crops. [1]
Common Hosts
- Tomatoes, Peppers, Eggplants
- Leafy greens (Lettuce, Spinach)
- Carrots, Brassicas
- Seedlings and transplants of most vegetables[1]
Citations
- [1] Cutworm - Wikipedia - https://en.wikipedia.org/wiki/Cutworm
- [2] Cutworms - UMN Extension - https://extension.umn.edu/yard-and-garden-insects/cutworms
- [5] Organic Plant Protection: Nails as Stem Protectors
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Copyright © 2025 Pacific Wolf Ltd. All rights reserved. Content and design may not be reproduced or distributed without permission.