Dealing with Spider Mites in a Hydroponic System

What Spider Mites Do

Spider mites are microscopic pests that pierce plant cells with their mouthparts and suck out contents, causing leaf stippling, bronzing, and fine webbing. Heavy infestations can stunt growth, defoliate plants, and reduce yields. [1]

Latin Name

Tetranychus urticae (two-spotted spider mite) [1]

Identification

Size: 0.4-0.7 mm; often red, green, or yellowish
Fine silk webbing on leaf undersides and stems
Leaf stippling ("bronzing") where cells have been emptied [2]
Leaves may curl, yellow, and drop under heavy pressure

Alternative Names

Two-spotted spider mite
Red spider mite (color morphs)
Green mite

Varieties (Common Species)

Tetranychus urticae (Two-spotted spider mite) [1]
Tetranychus cinnabarinus (Carmine spider mite) [1]
Panonychus ulmi (European red mite) [2]

Climates Where They Thrive

Hot, dry conditions (25-35 °C; RH ≤ 60 %) accelerate reproduction [3]
Populations decline under cool (< 15 °C) or very humid (> 75 % RH) conditions [2]

Companion Planting as Deterrents

Cultivar	Hydroponic Methods	Effectiveness
Garlic (Allium sativum)	All (DWC, NFT, Ebb & Flow, Drip)	High-sulfur volatiles repel [4]
Chives (Allium schoenoprasum)	All methods	High-similar deterrent effect [4]
Rue (Ruta graveolens)	All methods	Moderate-strong aroma confuses mites [5]
Basil (Ocimum basilicum)	NFT, DWC, Drip	Moderate-aromatic oils mask host cues [6]
Mint (Mentha spp.)	Wick, Kratky, Drip	Moderate-menthol scent disrupts landing [6]

Natural Predators

Predatory mite (Phytoseiulus persimilis) [7]
Predatory mite (Neoseiulus californicus) [7]
Ladybird beetles (Coccinellidae) [1]
Minute pirate bugs (Orius insidiosus) [8]
Green lacewing larvae (Chrysopidae) [1]

Remedies

Treatment	Hold Period	Natural?	Effectiveness
Insecticidal soap spray	1 day	Yes	Moderate-contact kill of nymphs & adults [2]
Neem oil emulsion	3 days	Yes	Moderate-feeding disruptor [6]
Horticultural oil	7 days	No	High-smothers eggs & adults [9]
Cold water spray	0 days	Yes	Low-dislodges mites; repeat often [10]
Predatory mites release	0 days	Yes	High-sustained biological control [7]

Other Remedies

Alcohol wipe: 70% isopropyl solution on leaves to dissolve cuticle.
Essential oil fogging: Disperse rosemary or peppermint oil to confuse mites [6]
Sticky barriers: Apply sticky tape around reservoir edges to trap crawling mites.
Acoustic disturbance: Low-frequency sound pulses to disrupt mating behavior.

Tips and Tricks

Maintain humidity ≥ 65 % and strong airflow to deter outbreaks [2]
Inspect leaf undersides under magnification weekly
Quarantine new plants under fine mesh before introduction
Rotate treatments bi-weekly to prevent resistance
Sanitize trays and tubing between crop cycles with dilute bleach

Common Hosts

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

Citations

[1] Spider mite - Wikipedia - https://en.wikipedia.org/wiki/Spider_mite
[2] Spider Mite Control in Greenhouses - UC IPM - https://ipm.ucanr.edu/PMG/PESTNOTES/pn7437.html
[3] Environmental Effects on Spider Mites - Journal of Acarology
[4] Allium Volatiles as Pest Deterrents - Pesticide Biochemistry and Physiology
[5] Companion Planting Principles - Wikipedia - https://en.wikipedia.org/wiki/Companion_planting
[6] Neem Oil for Spider Mite Management - Hydrobuilder Learning Center - https://learn.hydrobuilder.com/get-rid-of-spider-mites/
[7] Biological Control Agents for Spider Mites - Journal of Integrated Pest Management
[8] Orius Insidiosus in IPM - Clemson Cooperative Extension
[9] Horticultural Oils-Mode of Action - Journal of Economic Entomology
[10] Cold Water Sprays for Mite Management - Journal of Applied Entomology