How to treat a greenhouse for spider mites in autumn after harvest?

Understanding Spider Mites and Autumn Treatment

Why Autumn Treatment is Crucial

Treating a greenhouse for spider mites in the post‑harvest autumn period is indispensable for several practical reasons.

First, spider mite populations peak as temperatures rise in late summer. Without intervention, adult females lay thousands of eggs that survive the cooler months on plant debris, greenhouse structures, or in cracks. These overwintering stages become the primary source of infestation for the next growing cycle, leading to rapid colony expansion once temperatures increase.

Second, autumn conditions—lower humidity and reduced plant growth—limit the efficacy of natural predators such as predatory mites. Chemical or biological control applied before the dormant phase compensates for this shortfall, keeping mite numbers below economic thresholds.

Third, residual mite colonies on containers, benches, and irrigation equipment create a persistent reservoir. Targeted treatments after harvest remove these hidden populations, preventing cross‑contamination when new seedlings are introduced.

Fourth, early-season pesticide applications often encounter resistance development. Managing the pest during autumn reduces overall chemical pressure, preserving the effectiveness of existing products for future use.

Finally, autumn interventions align with greenhouse sanitation schedules. Cleaning, removing plant residues, and applying acaricides simultaneously maximize the impact of each action, ensuring a clean start for the upcoming season.

Key reasons for autumn treatment:

Elimination of overwintering eggs and juveniles
Compensation for reduced biological control activity
Removal of hidden reservoirs on infrastructure
Mitigation of resistance buildup
Integration with routine sanitation procedures

Implementing these measures before the greenhouse enters dormancy secures a low‑mite environment, safeguards the next crop, and maintains long‑term pest management efficiency.

Identifying Spider Mite Infestations

Spider mite presence becomes apparent through distinct visual cues on foliage. Adult mites and juveniles appear as tiny, moving specks, often red, brown, or yellow, and may be seen only with a magnifying lens. The most reliable indicator is stippling: a fine, pale network of spots where chlorophyll has been consumed, giving leaves a mottled appearance. As damage progresses, leaves develop a bronzed or silvered sheen and may curl or become brittle.

Key diagnostic signs include:

Fine webbing on leaf undersides, stems, and around the growing points; webs are most noticeable when sunlight catches them.
Small, pale pits or “silvering” on leaf surfaces, resulting from the feeding action of the mites.
Presence of moving specks when leaves are disturbed; shaking the plant over a white surface can reveal falling mites.
Decreased vigor, manifested as slowed growth, premature leaf drop, or reduced fruit set.

Systematic inspection improves detection accuracy. Begin with a thorough visual survey of the greenhouse’s lower canopy, where humidity and temperature favor mite proliferation. Use a 10‑20× hand lens to examine leaf undersides, paying particular attention to newly emerged foliage, which is most vulnerable. For quantitative assessment, collect leaf samples from multiple locations and place them in a shallow tray with a few drops of water; count mites under a stereomicroscope for an estimate of population density per leaf area.

Sticky traps positioned at canopy level provide ongoing monitoring. Replace traps weekly and record the number of mites captured; a consistent increase signals an escalating infestation. In addition, employing a water‑blotter method—pressing a moist white paper against leaf surfaces for several seconds—will transfer mites onto the paper for easier counting.

Accurate identification relies on combining visual symptoms, microscopic confirmation, and trap data. Early detection allows timely intervention, preventing the rapid population growth typical of spider mites during the cooler, post‑harvest autumn season.

Preparing the Greenhouse for Treatment

Removing Plant Debris and Remaining Harvest

Removing all plant residues and leftover produce is the first decisive step in suppressing spider‑mite populations after the crop season. Dead foliage, fallen fruits, and stems provide shelter and breeding sites, allowing mites to survive the cold months and re‑infest the next planting.

The clean‑out process should follow a strict sequence:

Cut back all remaining stems to ground level, using clean, sanitized tools to avoid transferring mites.
Gather and discard plant material in sealed bags or containers; composting is unsafe unless the material is heated to kill pests.
Sweep the floor, benches, and walkways to eliminate dust, soil particles, and mite eggs.
Vacuum or pressure‑wash surfaces, then allow them to dry completely before applying any chemical or biological control agents.
Inspect gutters, ventilation ducts, and any hidden corners; remove debris with a brush or compressed air.

After debris removal, conduct a visual inspection for remaining mites on any surviving foliage. If live individuals are detected, introduce predatory mites or apply an appropriate miticide according to label instructions. Completing the clean‑out thoroughly reduces the initial mite load, improves the effectiveness of subsequent control measures, and minimizes the risk of a resurgence in the upcoming growing cycle.

Cleaning Greenhouse Surfaces

Wiping Down Structures

After the crop is harvested, spider mites often survive on the greenhouse framework. Removing residual debris and plant material eliminates shelter and reduces the population that can re‑establish when temperatures rise.

Sweep all benches, tables, and support structures with a stiff brush to dislodge webbing and mite clusters.
Vacuum or collect the debris in sealed bags to prevent redistribution.
Wash surfaces with a mild detergent solution (1 % surfactant) to break down waxy residues that protect mites.
Rinse thoroughly with clean water and allow the structures to dry completely before covering or storing equipment.

A clean interior lowers the risk of overwintering mites and creates a hostile environment for any survivors, supporting effective autumn pest management.

Sweeping and Vacuuming

Sweeping and vacuuming are essential steps in reducing spider‑mite populations after the crop has been harvested. Removing senescent foliage, fallen fruit, and any organic residue eliminates the primary habitats where mites overwinter. A systematic sweep of the benches, aisles, and support structures should be performed before any chemical or biological treatment is applied.

A vacuum equipped with a fine‑mesh or HEPA filter extracts live mites and eggs from hard‑to‑reach crevices, cracks in the floor, and the undersides of benches. The device must generate sufficient suction to detach mites without dispersing them into the air. Operate the vacuum at a slow, steady pace, overlapping each pass by at least 20 cm to ensure complete coverage.

Key practices:

Conduct a thorough sweep immediately after harvest, then repeat weekly throughout the autumn period.
Follow each sweep with a vacuum pass on all surfaces, focusing on corners, drip trays, and ventilation ducts.
Empty the vacuum bag or canister into a sealed container after each session to prevent re‑infestation.
Clean and disinfect the vacuum filter regularly to maintain efficiency and avoid cross‑contamination.
Wear protective gloves and a mask to limit exposure to dust and mite fragments.

Combining diligent mechanical removal with subsequent biological or chemical controls creates an environment hostile to spider mites, reducing their survival rate and limiting the need for intensive pesticide applications later in the season.

Chemical Treatment Options

Selecting Appropriate Acaricides

Understanding Active Ingredients

Active ingredients determine the efficacy of mite control programs. Selecting compounds that remain effective at lower temperatures and reduced light levels is essential for post‑harvest greenhouse treatment. Systemic products, such as abamectin and spirodiclofen, are absorbed by plant tissue and protect new growth that emerges during the cooling period. Contact agents, including bifenthrin and lambda‑cyhalothrin, act on mites present on surfaces and provide rapid knock‑down.

When choosing an ingredient, consider residual activity, phytotoxic risk, and resistance management. Residual periods of 7–14 days allow for fewer applications, but prolonged exposure can increase the chance of resistance development. Rotating chemicals with different modes of action—e.g., alternating a pyrethroid with a phenylpyrazole—disrupts mite adaptation cycles.

Safety considerations include worker exposure and crop residue limits. Products labeled for post‑harvest use typically carry lower maximum residue values; verify compliance with local regulations before application. Protective equipment, ventilation, and adherence to label rates minimize health hazards.

Common active ingredients for autumn mite control:

Abamectin – systemic, high efficacy, limited to 10 °C minimum temperature.
Spirodiclofen – systemic, effective against egg and adult stages, low phytotoxicity.
Bifenthrin – contact, fast action, residual up to 14 days.
Lambda‑cyhalothrin – contact, broad‑spectrum, requires thorough coverage.
Pyriproxyfen – growth regulator, prevents mite reproduction, minimal residue.

Safety Precautions for Chemical Use

When addressing a post‑harvest autumn spider‑mite problem in a greenhouse, chemical interventions must be managed with strict safety protocols. Personal protective equipment (PPE) should be worn at all times: chemical‑resistant gloves, goggles, a full‑face respirator or mask with appropriate cartridges, and coveralls that prevent skin contact. Ensure that PPE is inspected for damage before each application and that it is removed and disposed of according to local hazardous‑waste regulations after use.

Before mixing or applying any pesticide, verify the product label for the correct concentration, required dilution water, and permissible temperature range. Use calibrated measuring devices to avoid overdosing. Prepare solutions in a well‑ventilated area, away from food preparation zones, and keep containers sealed when not in use. Record batch numbers, expiration dates, and application details in a logbook for traceability.

After treatment, follow these disposal and decontamination steps:

Collect leftover spray solution and rinse water in designated hazardous‑waste containers.
Clean equipment with soap and water, then rinse with a neutralizing solution if recommended by the manufacturer.
Store empty pesticide containers in a locked, labeled area until they can be returned to a licensed disposal facility.
Ventilate the greenhouse for the period specified on the label before re‑entering for routine work.

Adhering to these precautions minimizes health risks for workers, protects beneficial organisms, and prevents chemical residues from contaminating subsequent crops.

Applying Chemical Solutions

Proper Dilution and Application Methods

Effective control of spider mites after the crop is removed relies on precise dilution of miticides and correct application techniques. Use a water‑soluble product formulated for greenhouse use; follow the label’s recommended concentration, typically 0.5 ml L⁻¹ for oil‑based sprays and 1.0 ml L⁻¹ for aqueous solutions. Adjust the rate downward if temperatures drop below 10 °C, as mite activity and plant metabolism slow.

Apply the solution during the coolest part of the day, preferably early morning or late evening, to reduce evaporation and ensure leaf surface retention. Use a fine‑mist nozzle that produces droplets of 30–50 µm; this size maximizes coverage of the undersides of leaves where mites reside while minimizing runoff. Calibrate the sprayer so that each square meter receives 200–250 ml of mixture, providing a uniform film without excess moisture.

Maintain a strict schedule: treat the greenhouse at 5‑day intervals for three consecutive applications, then reassess mite counts before continuing. Record each dilution ratio, application volume, and environmental conditions to track efficacy and adjust future treatments.

Key points for dilution and application

Verify product compatibility with the greenhouse’s ventilation system.
Prepare fresh solution for each use; residual mixtures lose potency.
Wear protective gloves and goggles; rinse equipment with clean water after spraying.
Inspect foliage 24 hours post‑application; adequate coverage appears as a faint, even sheen on leaf surfaces.

Ensuring Thorough Coverage

Effective mite management in a greenhouse after the crop has been harvested requires complete contact between the product and every part of the plant and structure. Incomplete coverage leaves refuges for spider mites, allowing populations to rebound when temperatures rise.

Choose a delivery system that atomizes the solution into droplets fine enough to penetrate leaf undersides, yet large enough to reach stems and petioles. Pressure‑sprayers with adjustable nozzles or electrostatic sprayers meet these criteria.
Dilute the chosen acaricide or horticultural oil to the manufacturer’s recommended concentration. Over‑dilution reduces viscosity and compromises leaf adhesion; under‑dilution increases phytotoxic risk.
Apply the spray in two opposite directions, overlapping each pass by 10–15 %. This pattern eliminates gaps and ensures that both leaf surfaces receive adequate film.
Inspect foliage immediately after application. Use a handheld magnifier to verify that the undersides of leaves, especially near the crown, display a uniform sheen. Re‑spray missed spots before the solution dries.
Treat non‑plant surfaces—bench tops, support frames, and ventilation ducts—because spider mites can inhabit these areas. Use a misting nozzle to coat vertical and horizontal surfaces evenly.
Record the time, temperature, humidity, and wind speed at each application. Optimal conditions (15–25 °C, 60–80 % relative humidity, low air movement) promote thorough film formation and reduce runoff.

Following these steps guarantees that the acaricidal treatment reaches all potential mite habitats, minimizing the risk of resurgence during the cooler autumn period.

Non-Chemical Treatment Methods

Heat Treatment (Solarization)

Principles of Solarization

Solarization exploits solar heat to create an inhospitable environment for spider mites and their eggs on greenhouse surfaces and in the substrate after the crop has been removed. The method relies on trapping solar radiation under a clear polyethylene film, raising temperatures to lethal levels for the pest.

The process begins with thorough cleaning: remove plant debris, wash benches, and clear soil of residues. Place a transparent plastic sheet over the entire greenhouse floor, walls, and any remaining soil, ensuring the material is free of tears. Seal the edges with tape or weighted sandbags to prevent air exchange. During the brightest days of autumn, the film concentrates sunlight, elevating surface temperatures to 45‑55 °C. Maintain this cover for a minimum of 5–7 consecutive days, monitoring temperature with a probe to confirm lethal thresholds are reached for at least 12 hours each day.

After the exposure period, remove the plastic, ventilate the space, and inspect for surviving mites. If populations remain, repeat the solarization cycle or combine it with a brief application of a miticide approved for post‑harvest use. Consider the following practical points:

Timing: Short daylight hours and cooler ambient temperatures in autumn may extend the required exposure; start the treatment early in the day and keep the cover on through night to retain heat.
Moisture control: Slightly dampen the substrate before covering to improve heat conduction, but avoid excess water that could promote fungal growth.
Material selection: Use UV‑stable, clear polyethylene of at least 0.06 mm thickness; thicker films reduce heat transmission.
Safety: Ensure the greenhouse is empty of workers during the heating phase to prevent burns; wear protective gloves when handling the plastic.

When executed correctly, solarization reduces spider mite populations to negligible levels, prepares the greenhouse for the next planting cycle, and eliminates the need for chemical residues in the post‑harvest period.

Steps for Effective Heat Treatment

Effective heat treatment requires precise preparation, controlled temperature, and thorough monitoring to eradicate spider mites from a greenhouse after the autumn harvest.

First, clear the structure of all plant debris, harvested produce, and loose soil. Remove any organic material that could shelter pests or retain moisture, as it interferes with heat penetration. Clean surfaces with a disinfectant solution to reduce microbial load before heating.

Second, seal the greenhouse to prevent heat loss. Close vents, doors, and any gaps in the covering material. Install temporary insulation, such as thermal blankets or reflective panels, to maintain a uniform temperature throughout the space.

Third, raise the internal temperature to a lethal range for spider mites. Research shows that exposure to 45 °C (113 °F) for at least 30 minutes kills all mobile stages. Use electric heaters, propane burners, or solar‑heat collectors to achieve the target. Increase temperature gradually—no more than 5 °C per hour—to avoid plant shock if any crops remain.

Fourth, monitor temperature continuously with calibrated thermometers placed at multiple locations: near the floor, mid‑canopy, and ceiling. Verify that the lethal temperature is sustained for the required duration at each point. Adjust heating equipment instantly if any zone falls below the threshold.

Fifth, after the exposure period, allow the greenhouse to cool slowly. Maintain airflow to equalize temperature and prevent condensation, which could foster fungal growth. Once the internal temperature drops below 30 °C (86 °F), reopen vents and restore normal ventilation.

Sixth, conduct a post‑treatment inspection. Examine leaves, stems, and soil for any surviving mites or eggs. Use a handheld magnifier or sticky traps to confirm eradication. If residual activity is detected, repeat the heat cycle with the same parameters.

Seventh, implement preventive measures to avoid reinfestation. Apply horticultural oil or botanical miticides before the next planting cycle, and establish a regular sanitation schedule that includes cleaning, debris removal, and periodic temperature checks during cooler months.

By following these steps—clearing debris, sealing the environment, achieving and verifying lethal heat, cooling methodically, and confirming results—growers can reliably eliminate spider mite populations and protect greenhouse assets during the post‑harvest period.

Biological Control Agents

Introducing Predatory Mites

Introducing predatory mites is an effective biological strategy for managing spider‑mite populations in a greenhouse after the harvest season. These natural enemies locate and consume all mobile stages of spider mites, reducing reproduction rates and preventing rapid colony expansion during the cooler autumn months. Their activity continues as long as suitable humidity and temperature conditions are maintained, allowing growers to keep pest levels below economic thresholds without chemical interventions.

For successful implementation, follow these precise steps:

Select species adapted to the greenhouse environment, such as Phytoseiulus persimilis for high spider‑mite pressure or Neoseiulus californicus for broader temperature tolerance.
Prepare the release area by removing debris, adjusting ventilation, and ensuring relative humidity stays between 60 % and 80 % to support mite survival.
Apply a calibrated dose, typically 100–200 predatory mites per square meter, evenly distributed on foliage using a fine‑mist sprayer or manual placement.
Monitor mite activity weekly with a hand lens; increase releases by 20 % if spider‑mite counts exceed the threshold of five mobile individuals per leaf.
Avoid broad‑spectrum insecticides that could harm the introduced predators; if chemical control is unavoidable, choose products with proven low toxicity to predatory mites and apply them at the minimum effective rate.

Maintaining these practices throughout the autumn period secures long‑term suppression of spider mites, preserves plant health for the next cropping cycle, and reduces reliance on synthetic pesticides.

Timing and Conditions for Release

The release of predatory mites must occur when residual spider‑mite populations are detectable but before winter temperatures drop below their activity threshold. Monitor leaf debris and any surviving plants for signs of spider‑mite activity within one to two weeks after the final harvest. Initiate releases as soon as the first infestation is confirmed, preferably before the first frost.

Optimal conditions for successful establishment include:

Temperature: 15 °C – 25 °C; activity declines sharply below 12 °C.
Relative humidity: 60 % – 80 %; low humidity reduces predatory mite mobility and reproduction.
Light: natural daylight cycles; supplemental lighting is unnecessary if ambient light remains above 300 lux.
Air circulation: gentle airflow prevents leaf surface condensation and encourages mite dispersal.

Apply the biological agent at the recommended field rate, distributing evenly across all remaining plant material and debris. After application, maintain the above environmental parameters for at least five days to allow predator colonization. If temperatures fall below 12 °C, postpone release until a warm spell restores suitable conditions, or use a protected micro‑environment such as a heated section of the greenhouse. Continuous monitoring should follow each release to verify predator establishment and to schedule additional applications if mite counts rise.

Horticultural Oils and Soaps

Application of Neem Oil

Neem oil provides a botanical control option for spider mites that persist in greenhouse structures after the crop has been harvested. Its active compounds disrupt mite feeding and reproduction without leaving harmful residues when applied correctly.

Prepare a spray solution using cold‑pressed neem oil at 1–2 % v/v. Mix the oil with a non‑ionic surfact surfactant (0.1 % of the total volume) to ensure even distribution. Dilute the mixture in clean water to the volume required for the greenhouse space.

Apply the solution with a fine‑mist sprayer, covering all leaf surfaces, stems, and the undersides of foliage. Perform applications in the late afternoon or early evening to minimize photodegradation. Repeat at 5‑ to 7‑day intervals until mite populations decline below economic thresholds.

Observe environmental parameters: temperature should stay between 15 °C and 30 °C, relative humidity above 50 %, and direct sunlight on wet surfaces should be avoided. These conditions preserve the efficacy of the active ingredients.

Wear protective gloves, goggles, and a mask during mixing and spraying. Ensure adequate ventilation after treatment to prevent buildup of vapors. Do not apply neem oil to stored produce or surfaces that will contact food without a post‑treatment waiting period of at least 24 hours.

Combine neem oil use with sanitation measures: remove plant debris, clean benches, and vacuum settled mites. Monitor mite activity with sticky traps or visual inspections to adjust treatment frequency.

Store unopened neem oil containers in a cool, dark place. Once opened, keep the product tightly sealed and use within six months to maintain potency.

Using Insecticidal Soaps

Insecticidal soaps provide a reliable option for managing spider mites in a greenhouse after the autumn harvest. The product penetrates the mite’s exoskeleton, causing rapid desiccation without harming most beneficial insects when applied correctly.

Apply the soap when humidity is moderate (50‑70 %) and temperatures are above 15 °C. Use a concentration of 1‑2 % (10‑20 ml of commercial concentrate per litre of water). Spray until runoff covers all leaf surfaces, including undersides where mites congregate. Repeat applications every 5‑7 days until monitoring shows fewer than two mites per leaf.

Key considerations:

Timing: Treat early in the evening to reduce leaf burn from direct sunlight.
Coverage: Ensure thorough wetting of foliage; missed spots allow mite populations to rebound.
Resistance management: Rotate with botanical oils or predatory mites to prevent adaptation.
Safety: Wear gloves and eye protection; avoid contact with foliage of plants sensitive to surfactants (e.g., lettuce, beans).

After the final spray, remove plant debris and clean greenhouse benches. This eliminates residual mite eggs and reduces the risk of re‑infestation during the dormant period. Regular scouting throughout the winter months confirms the effectiveness of the soap treatment and informs any necessary follow‑up actions.

Post-Treatment Measures and Prevention

Ventilating the Greenhouse

Ventilation is essential for reducing spider‑mite populations after the crop has been harvested. Proper air exchange lowers leaf temperature, decreases relative humidity, and disrupts the microclimate that favors mite development.

During autumn, external temperatures drop, making it necessary to balance heat retention with airflow. Open side vents and roof vents early in the morning when ambient temperature is above the greenhouse’s internal temperature. Keep vents open for at least 30 minutes to flush out warm, humid air. If the greenhouse is equipped with exhaust fans, run them on a low setting for 10–15 minutes after each venting session to enhance circulation.

Maintain a target relative humidity of 50 %–60 % and a leaf temperature of 20 °C–22 °C. Use a hygrometer and thermometer to monitor conditions; adjust vent openings accordingly. When humidity rises above the target range, increase vent size or add supplementary fans. When temperatures fall below the optimal range, narrow vents partially to retain heat while still allowing fresh air to enter.

A practical checklist for autumn ventilation:

Open lower side vents for 30 minutes each morning.
Open roof vents for an additional 15 minutes after side vents.
Activate exhaust fans for 10 minutes after venting.
Record temperature and humidity every hour.
Reduce vent opening if temperature drops below 20 °C; increase if humidity exceeds 60 %.

Consistent ventilation prevents mite eggs from maturing, limits colony expansion, and prepares the structure for winter protection measures.

Monitoring for Re-infestation

Effective monitoring after harvest is essential to prevent spider‑mite resurgence during the autumn period. Visual inspections should begin immediately after crops are removed and continue weekly until the greenhouse is sealed for winter. Each inspection must include the undersides of leaves, petioles, and any remaining plant debris, using a 10× hand lens to detect early colonies.

Key actions for each visit:

Record the number of mites per leaf segment on a standardized chart.
Deploy yellow sticky traps at canopy height; replace them every 7 days and count captured mites.
Sample at least five random plants per bench, examining ten leaves per plant.
Measure temperature and relative humidity; maintain values below 20 °C and 60 % RH to suppress mite development.
Compare counts to established action thresholds (e.g., >5 mites per leaf segment) and initiate control measures only when thresholds are exceeded.

Maintain a log that details date, location, mite counts, trap results, and environmental readings. Trend analysis of this data reveals patterns of re‑infestation and informs timing of preventative treatments such as miticides, biological agents, or cultural adjustments. Prompt detection and documentation reduce the risk of a full‑scale outbreak before the greenhouse enters dormancy.

Future Prevention Strategies

Crop Rotation

Crop rotation reduces spider‑mite pressure in greenhouse systems after the autumn harvest. By replacing the previous host crop with a non‑susceptible species, the mite population loses its primary food source, leading to a decline in numbers before the next planting cycle.

Effective rotation strategies include:

Selecting a crop that is poor or non‑host for Tetranychus spp., such as leafy greens after cucurbits.
Maintaining a minimum two‑year gap between susceptible crops in the same bed.
Incorporating trap crops at the perimeter to attract and concentrate mites away from the main production area.
Combining rotation with thorough cleaning of benches, gutters, and equipment to eliminate residual eggs and debris.

Implementing these practices alongside environmental controls—lowering temperature, reducing humidity, and limiting plant canopy density—contributes to a sustainable reduction of spider‑mite populations, preparing the greenhouse for the next growing season.

Maintaining Greenhouse Hygiene

Maintaining strict hygiene in a greenhouse after the autumn harvest reduces spider‑mite populations and prevents reinfestation. All plant material must be removed promptly; discard or burn residues that could harbor eggs or mobile stages. Clean benches, trays, and support structures with a detergent solution, then rinse with water and allow to dry completely before re‑use.

Inspect the soil surface for dead roots or organic mulch. Remove contaminated soil layers and replace with fresh, sterilized substrate when feasible. If soil reuse is unavoidable, treat it with a soil‑drench of neem‑based oil or a low‑toxicity acaricide, following label rates and allowing sufficient drying time before planting.

Ventilation and humidity control are integral to sanitation. Reduce relative humidity to 50–60 % by increasing airflow and using dehumidifiers; lower moisture limits mite reproduction. Ensure fans, vents, and exhaust ducts are free of dust and fungal growth, cleaning them with a mild alkaline solution weekly.

Implement a routine disinfection schedule:

Weekly: wipe all work surfaces, tools, and handheld equipment with a 70 % ethanol solution.
Bi‑weekly: spray structural frames, walkways, and guttering with a horticultural soap concentrate.
Monthly: conduct a thorough cleaning of the greenhouse covering, removing any accumulated debris that could shield mites.

Monitor traps and sticky cards placed near entry points. Replace cards when they become saturated, and record mite counts to detect early increases. Promptly isolate any new plants showing signs of infestation, and subject them to a pre‑plant quarantine treatment before introduction to the main area.

By adhering to these sanitation measures, the greenhouse environment remains hostile to spider mites, supporting healthier crops for the next production cycle.

Inspecting New Plants

Inspect new arrivals before they join the existing crop. Place each plant in an isolated area for at least 48 hours, keeping temperature and humidity consistent with the greenhouse environment. During this period, examine foliage, stems, and undersides for any signs of spider mite activity.

Look for fine webbing on leaf surfaces, especially along veins and on the lower side of leaves.
Identify stippled or yellowed spots where mites have fed; these lesions often appear as tiny, irregular patches.
Count mites if visible; a few individuals may be tolerable, but any colony larger than a few dozen indicates a potential outbreak.
Check for accompanying predators such as lady beetles or predatory mites; their presence can mitigate risk but does not eliminate the need for further action.

If inspection reveals infestation, remove the plant from the greenhouse, treat with a miticide approved for autumn use, or discard if control is unlikely. For clean plants, apply a preventative spray of horticultural oil or a mild soap solution before integrating them with the main stock. This routine reduces the likelihood of spider mite spread during the vulnerable post‑harvest period.