Dealing with Thrips in a Hydroponic System

What Thrips Do

Thrips are tiny, slender insects that rasp plant cells with their mouthparts and suck out the contents, causing silvery speckling, distorted growth, and black fecal spots. They reproduce rapidly and can transmit tospoviruses, leading to significant crop damage. [1]

Latin Name

Thysanoptera (order of thrips) [1]

Identification

Very small (1-2 mm), narrow-bodied insects with fringed wings
Yellow, brown, or black coloration
Active jumpers; often congregate on new growth and flowers [2]
Feeding damage appears as silvery or bronze flecking on leaves

Alternative Names

Thunderflies
Storm bugs
Flower thrips
Leaf thrips

Varieties (Common Species)

Western flower thrips (Frankliniella occidentalis)
Onion thrips (Thrips tabaci)
Greenhouse thrips (Heliothrips haemorrhoidalis)
Melon thrips (Thrips palmi)
Chili thrips (Scirtothrips dorsalis)

Climates Where They Thrive

Warm, dry conditions (25-32 °C, RH ≤ 60 %) encourage rapid reproduction [3]
Populations decline in cool (< 15 °C) or very humid (> 75 % RH) environments [4]

Companion Planting as Deterrents

Cultivar	Hydroponic Methods	Effectiveness
Chrysanthemum (Tanacetum cinerariifolium)	All (DWC, NFT, Ebb & Flow, Drip)	High - produces pyrethrins that repel thrips [5]
Marigold (Tagetes spp.)	All	Moderate - thiophenes deter feeding [5]
Basil (Ocimum basilicum)	NFT, DWC, Drip	Moderate - aromatic oils mask plant cues
Mint (Mentha spp.)	Wick, Kratky, Drip	Moderate - strong scent disrupts landing

Natural Predators

Predatory mites (Amblyseius cucumeris) [2]
Minute pirate bugs (Orius insidiosus) [2]
Green lacewing larvae (Chrysopidae) [1]
Predatory thrips (Scolothrips sexmaculatus) [1]
Parasitic wasps (Megaphragma spp.) [1]

Remedies

Treatment	Hold Period	Natural?	Effectiveness
Insecticidal soap spray	1 day	Yes	Moderate - contact kill of nymphs [6]
Neem oil emulsion	3 days	Yes	Moderate - repellent & feeding disruptor [6]
Spinosad spray	7 days	No	High - ingestion toxin with residual effect [7]
Blue sticky traps	0 days	Yes	Low - monitoring & some adult capture
Horticultural oil spray	7 days	No	Moderate - smothers eggs & larvae [6]

Other Remedies

Reflective mulch: Confuses adults and reduces landing [5]
UV LED traps: Attract and trap adults at night
Acoustic deterrents: Low-frequency sounds to disrupt mating
Essential oil diffusion: Disperse lavender or rosemary oils
Water-mist shock: High-pressure mist to knock off nymphs

Tips and Tricks

Inspect underside of leaves daily under magnification
Maintain high humidity (≥ 65 %) and good airflow to reduce outbreaks [4]
Quarantine new plants under fine mesh for 7-10 days
Rotate treatments weekly to prevent resistance
Clean and sanitize trays between crop cycles

Common Hosts

Tomatoes, Peppers, Cucumbers
Leafy greens (Lettuce, Spinach)
Herbs (Basil, Mint)
Strawberries, Ornamentals

Citations

[1] Thrips - Wikipedia - https://en.wikipedia.org/wiki/Thrips
[2] Greenhouse Thrips Management - UC Davis IPM - https://ipm.ucanr.edu/PMG/PESTNOTES/pn7425.html
[3] Thrips Biology and Control in Protected Culture - Ontario Ministry of Agriculture
[4] Environmental Effects on Thrips Populations - Journal of Applied Entomology
[5] Companion Plants for Pest Control - Epic Gardening - https://www.epicgardening.com/companion-planting-guide/
[6] Insecticidal Soaps & Oils in Hydroponics - Eden Green Technology - https://www.edengreen.com/blog-collection/types-of-hydroponics-pests
[7] Spinosad Efficacy Against Thrips - Journal of Economic Entomology