Tiny sap-feeding mites that live mostly on leaf undersides and damage plants by piercing cells, causing pale stippling, bronzing, leaf drop, fine webbing, and.
Identification
Body size: Spider mites are very small and may look like moving specks on leaf undersides; a hand lens helps confirm them.
Leaf stippling: Feeding removes cell contents and creates fine yellow, white, or pale stippling on leaves.
Webbing: Heavy infestations produce fine webbing around leaf undersides, growing tips, petioles, and stems.
Leaf bronzing: As feeding increases, leaves may turn bronze, gray, dusty, or scorched before dropping.
Underside colonies: Mites, eggs, and cast skins are usually concentrated along veins and protected leaf undersides.
Eggs: Eggs are small, round, and often laid on leaf undersides near adult mites.
Movement: Adults and nymphs crawl slowly; tapping leaves over white paper can reveal moving mites.
Lookalikes
Thrips: Thrips cause silvery scarring and black fecal specks, but are slender insects rather than tiny mites and do not create spider-like webbing.
Aphids: Aphids are larger soft-bodied insects that cluster on shoots and produce sticky honeydew rather than fine stippling and webbing.
Powdery mildew: Powdery mildew produces white fungal patches on leaf surfaces, not moving mites, eggs, and webbing on undersides.
Nutrient deficiency: Deficiencies can cause yellowing or mottling, but do not produce webbing, eggs, cast skins, or crawling mites.
Environmental Triggers
Hot air temperature: Warm to hot conditions speed spider mite development and reproduction.
Low relative humidity: Dry air favors spider mite outbreaks and reduces some natural enemy effectiveness.
Moderate to high relative humidity: Higher humidity can slow spider mite population growth, though foliage disease risk must still be managed.
Dusty or stressed foliage: Dust, heat stress, and water stress make plants more vulnerable and can reduce predator performance.
Dense canopy: Dense foliage creates protected leaf undersides where colonies can build unnoticed.
Plant contact and airflow movement: Mites spread by crawling between touching plants and by movement on clothing, tools, airflow, and webbing.
High sanitation and scouting: Removing infested leaves and detecting colonies early prevents explosive outbreaks.
Treatment
Routine underside scouting: Inspect leaf undersides at least twice per week during warm dry periods. Use a hand lens to check along veins and protected canopy areas. Tap suspect leaves over white paper and look for moving specks. Mark and recheck hotspot plants to track spread.
Remove infested leaves or hotspots: Remove heavily stippled or webbed leaves when plant growth allows. Bag infested foliage before carrying it through the grow area. Avoid brushing infested leaves against healthy plants. Sanitize hands and tools after handling infested plants.
Water spray knockdown: Spray leaf undersides and stems with enough force to dislodge mites without damaging plants. Repeat every 2-3 days during early infestations. Increase airflow afterward so foliage dries quickly. Avoid this method on crops prone to foliar disease if leaves will stay wet.
Predatory mites: Select predator species matched to temperature, humidity, and infestation level. Release early before heavy webbing develops. Avoid broad-spectrum pesticides before and after release. Maintain humidity and canopy conditions suitable for the predator species. Monitor both spider mites and predators weekly.
Predatory insects: Use supplier guidance for release rates and compatible crops. Introduce predators early or alongside predatory mites for broader coverage. Avoid pesticide residues that harm beneficial insects. Maintain scouting to confirm predator establishment and prey reduction.
Insecticidal soap or horticultural oil: Use only products labeled for edible crops and the specific crop type. Test on a small area first, especially on tender herbs. Spray leaf undersides thoroughly where mites and eggs are located. Avoid spraying during high heat or intense light to reduce leaf burn risk. Repeat according to label directions because contact products have limited residual effect.
Labeled miticide program: Use only products labeled for spider mites, edible crops, and the production environment. Rotate modes of action to reduce resistance risk. Follow all label rates, restricted-entry intervals, and preharvest intervals. Avoid unapproved products in recirculating hydroponic systems. Combine with leaf removal, scouting, and biological controls where compatible.
Humidity and plant stress management: Avoid hot dry canopy conditions where possible. Maintain crop-appropriate humidity without promoting fungal disease. Keep plants evenly irrigated and avoid nutrient or water stress. Reduce dust and clean walkways, benches, and intake areas.
Quarantine incoming plants: Inspect new plants carefully before introducing them to the grow area. Hold incoming plants separately for observation where practical. Reject plants with stippling, webbing, eggs, or mites. Do not keep ornamental plants or unmanaged hosts near production crops.
Companion planting is not reliable mite control: Do not rely on companion planting as the primary treatment. Avoid overcrowded mixed plantings that hide leaf undersides. Use companion plants only if they improve habitat for beneficials without increasing mite refuges. Prioritize scouting, predators, sanitation, and labeled contact controls.
Lifecycle
Egg laying on leaf undersides: Adult females lay round eggs on leaf undersides, often near veins and within protected canopy areas.
Egg hatch: Eggs hatch into larvae that begin feeding on leaf cells soon after emergence.
Larval and nymph feeding: Immature mites feed and molt through several stages, creating stippling and increasing colony density.
Reproductive adult: Adults reproduce quickly under warm dry conditions, allowing populations to rise sharply.
Webbing and dispersal: Heavy colonies produce webbing and mites move to nearby leaves or plants by crawling, airflow, tools, clothing, or plant contact.
Outbreak and plant decline: Multiple overlapping generations cause bronzing, leaf drop, reduced photosynthesis, and crop quality loss.