Grey mould rarely starts across the whole greenhouse.

11.08.2026.

Plant health / Malta

Grey mould rarely starts across the whole greenhouse.

Botrytis first finds what has been overlooked: a spent flower in a leaf axil, a damaged stem, touching wet leaves or rotting young fruit. After cool, humid nights, these small weak points can become starting points.

Botrytis cinerea is widespread. When spores meet susceptible tissue and persistent surface moisture, the familiar grey spore growth can appear quickly. The sensible response is not a rushed spray treatment, but a calm sequence: check symptoms, contain the outbreak, remove material, dry the crop and then improve prevention.

Principle for this evening: Do not leave dead, damaged or wet material between plants while the greenhouse cools.

First response / act before diagnosis becomes a debate

Move calmly. Remove precisely.

A fluffy coating does not automatically prove Botrytis. Tissue with typical grey spore growth, soft collapse or an advancing lesion should still be handled carefully. An open basket, vigorous shaking or hosing down can spread spores and infected particles further through the greenhouse.

01
Pause ongoing care.
Do not keep pruning, harvesting or brushing through neighbouring plants before dealing with the suspicious area.
02
Bag it at the plant.
Place a bag or sealable container beside the plant before cutting. Transport infected material closed, never exposed.
03
Remove visibly affected tissue completely.
Use clean, sharp tools and carefully cut away the flower, fruit or leaf, including soft collapsed sections.
04
Read the surroundings, not only the lesion.
Look for condensation, wet foliage, stagnant air, close leaf contact and plant debris on benches and floors.

A sound structural base with accessible ventilation and clear working routes is offered by the Classic aluminium greenhouse. Daily crop care remains decisive: you should be able to inspect plants closely, clean surfaces easily and respond to weather changes without moving every plant.

Recognition / do not call every coating Botrytis

Read the pattern first, then respond.

Grey mould often appears as a dusty, fluffy grey to grey-brown coating on affected flowers, leaves, stems or fruit. From a distance, normal ageing, other moulds, cold damage and root-related wilting can look similarly alarming. Assess the tissue, its position and the climate conditions of recent days together.

Grey spore growth

Soft collapse

Dry ageing

More typical of grey mould

Fine grey, slightly dusty spore growth on soft or dead tissue; browning flowers; lesions starting from an old flower, wound or damaged fruit; or a stem area where a leaf, support clip or petal stayed wet for a long time.

Grey spores are a strong indication, especially when infection begins on ageing tissue and moisture has persisted. They do not replace a careful assessment of the whole picture.

Collapse without visible fluff

Watery, brown or pale-brown tissue can occur before Botrytis sporulates visibly. It may also indicate another rot, mechanical injury, cold damage, a root problem or bacterial disease. Check whether the crown, roots, leaf edges or only a single wound are affected.

If valuable plants, young plants or food crops are affected, isolate the suspect plant and seek professional advice or a plant diagnosis for unclear or recurring symptoms.

Normal senescence

A dry faded flower or an evenly yellowing lower leaf is not automatically infected. It becomes an opportunity for Botrytis when it remains in a damp, shaded crop or sticks to fruit and leaves.

The practical distinction: remove healthily ageing material during routine care. Carefully contain, bag and hygienically dispose of soft, spotted or fluffy suspect material.

Map of weak points – markers show risks, not proven infections.

1 / Spent flowers Ageing petals hold moisture against young fruit, leaves or stems.

2 / Leaf contact Leaves pressed together remain shaded and dry more slowly after watering or condensation.

3 / Pruning wounds Fresh cut surfaces need clean work and quick drying rather than lasting moisture.

4 / Fruit damage Cracks, feeding damage and bruises create vulnerable areas, particularly in humid weather.

5 / Plant debris Leaves, flowers and fallen fruit on benches or floors can continue producing spores close to the crop.

6 / Stem lesions Brown to pale-brown areas around wounds, clips or dying leaves should be checked promptly.

Where the fungus enters

Botrytis favours the places good greenhouse care already keeps in view.

Botrytis colonises old, injured and dying plant tissue particularly easily. That does not make it harmless. Once established on a dead flower, wounded stem or soft fruit, spores can be carried onward by airflow, splashing water, hands, clothing and tools.

In a home greenhouse, risks are often visible before disease is noticed. Tomato flower remains collect in leaf axils, while broad cucumber leaves lie against each other. Pelargoniums, fuchsias and begonias retain faded flowers, and strawberries can hold petals and ripening fruit in the same damp pocket. These are opportunities for Botrytis, not inevitable infections.

Inspect after cool, overcast days. At midday the house may seem unremarkable, although leaves and flowers were wet from evening well into the morning.
Work on healthy, dry plants first. Attend suspect areas last; then clean hands and tools before touching healthy plants again.
Keep floors and bench surfaces visible. On clear, clean surfaces, petals, leaves and spoiled fruit are noticed immediately.

The key interval / from evening to a dry leaf

Humidity matters. Surface wetness says more.

Relative humidity is a useful signal, but not a complete diagnosis. Risk rises when leaves, flowers and stems reach the dew point as they cool and stay wet for a long time. Condensation on glazing is therefore not merely a visual or housekeeping issue. It shows that greenhouse moisture conditions have developed which should also be checked and corrected on cool plant surfaces.

Late afternoon

Sunset

Night

Early morning

After sunrise

Water with time to dry

Water early enough for splashes and damp surfaces to dry before the evening cools. Water belongs around the roots, not over leaves and flowers.

Temperature falls

Glazing, metal and plant surfaces cool quickly. Dense crops and still corners often lose heat and air exchange first.

Condensation risk rises

Humid air meets cold surfaces. Leaves can become wet even when no obvious droplets are visible and daytime hygrometer readings were not extreme.

Break the wet period

According to weather and equipment, use a coordinated combination of gentle heat, controlled ventilation and soft air circulation to dry plant surfaces.

Check and adjust

Inspect inside the crop, not just the panes. If it remains wet, adjust watering time, plant spacing, air movement or climate management.

There is no universal number of wet hours that reliably predicts infection for every crop, variety and temperature. Use this period as a practical observation routine: avoid a long, cool wet phase on susceptible tissue. Cornell guidance likewise stresses the importance of preventing condensation on plant surfaces for Botrytis control.

A greenhouse with easy-to-use roof ventilation provides a good basis for daily climate management. The Classic aluminium greenhouse has roof vents; automatic vent openers can support a more dependable everyday response. Weather observation and crop inspection remain essential.

Spacing

Create air routes, not merely decorative gaps.

Position pots and grow bags so leaves do not continually push into one another. Tie tomatoes and cucumbers in promptly, remove low or diseased leaves and make room before flowering crops become a closed wall. A small circulation fan can reduce still, damp zones. It should move air gently through the crop instead of blowing strongly at one plant all the time.

Watering

Water the root zone and protect the evening.

Drip irrigation, a gently directed watering can at the pot edge or other low-level methods keep foliage drier. Early watering gives unavoidable splashes time to dry; late watering can create a wet night-time period. Adjust the amount to weather and plant needs. A humid, cloudy week needs a different rhythm from a bright, warm Maltese summer spell.

Pruning

Carry out clean work on dry crops.

Prune, side-shoot and harvest where possible when foliage is dry, using clean, sharp tools. Avoid unnecessarily large wounds. Remove faded flowers and yellow leaves before more extensive pruning. With several plant groups, start in the healthiest area and finish where suspect symptoms are present.

Season

Expect problems when light and drying power decline.

In Malta, pay particular attention during cooler, humid winter periods, unsettled spring weather and damp autumn conditions. A greenhouse can seem calm while the crop cools quickly after sunset and stays wet for long periods. During bright, hot summers, ventilation and shading may be central; in cooler phases, use controlled air exchange, circulation and, where equipped, moderate warmth without chilling the crop.

For forward-looking climate management, consider the Classic aluminium greenhouse, particularly for its usable roof vents and the option to make door opening and gentle air circulation part of the daily routine.

Hygiene / the transport route matters

Do not carry the problem through the crop.

Removal works best when suspect material is contained from the moment it is found. Think of a short, direct route from plant to closed waste container – not a tour through the whole greenhouse with an open harvest basket.

Dead flowers, diseased leaves and rotting fruit belong neither under the bench nor directly outside the greenhouse door, nor in an open compost bucket near plants. They can remain a source of spores.

At the site

Cut

Contain

Remove

Reset

At the plant

Before cutting, bring a bag or sealable container directly to the affected plant.

This means the material is moved less and does not brush against healthy leaves.

The cut

Remove diseased, soft or visibly sporulating tissue with a clean, sharp tool.

A clean cut is easier to monitor and avoids an unnecessarily large tear wound.

Containment

Put the material straight into the bag and close it before leaving the area.

Do not shake it, place it on a bench or carry it through the crop in an open basket.

Disposal

Take waste out of the greenhouse promptly and dispose of it through household or organic waste where local arrangements permit.

Do not store a rotting pile immediately beside doors, windows or other ventilation openings.

Restart

First remove plant debris mechanically from secateurs and work surfaces. Then clean tools with a suitable product following the manufacturer’s instructions; clean hands or gloves too before touching healthy plants again.

Physical cleaning comes first. Attached plant matter can prevent a cleaning or disinfecting product from reliably reaching the surface.

Make this sequence a weekly routine instead of saving it for acute outbreaks. Clear work surfaces, accessible routes and durable components make a greenhouse easier to maintain as a productive workspace. Discover the Classic aluminium greenhouse and plan its layout around how you actually grow, inspect, ventilate and clean.

Treatment / prevention after correction

Products can help. They do not replace a clean, dry greenhouse.

When Botrytis is active, first remove affected plant parts and correct the conditions that favour it. Fungicides or biological plant-protection products may only be considered as part of an integrated approach to protect still-healthy tissue. Rotting or destroyed plant material does not become healthy again after treatment.

Task A

Use cultivation measures as the first treatment.

Remove spent flowers, affected fruit, dead leaves and other plant debris immediately.
Reduce surface wetness through earlier watering, controlled ventilation, appropriate warmth and gentle air circulation.
Increase plant spacing and consistently open damp, compressed areas of foliage.
Check neighbouring plants and the bench and floor below the infected area carefully.

Task B

Choose plant-protection products precisely for the crop and authorisation.

Use the Malta register lookup, then verify that the product is currently authorised for the crop, target organism, greenhouse use and user category.
Follow the complete current label, including instructions on use, dose, protective clothing, ventilation, waiting period and permitted application frequency.
For repeated applications, consider resistance management and do not rely permanently on the same mode of action.
Do not use a product simply because it is authorised for another ornamental, vegetable crop or outdoor use.

Biological options: preventive, specific and authorisation-dependent.

Biological plant-protection products or antagonists can be one element in certain crops and production systems. Their value depends on the product, formulation, crop, timing, temperature, disease pressure and correct application. They are generally most useful before the disease is firmly established and alongside hygiene and moisture management. “Biological” does not automatically mean a product suits every vegetable, ornamental or greenhouse crop, or is authorised for home use.

Conventional fungicides: a professional decision, not a standard reflex.

If an authorised fungicide is professionally justified by crop value and ongoing disease pressure, selection must also consider possible resistance. Botrytis is known for resistance problems. Avoid improvised mixes, altered doses and routine calendar treatments without a specific risk. For severe stem infection, multiple centres or recurring outbreaks, seek expert crop-specific advice.

Authorisation rule in Malta: Use the Malta register lookup to find the relevant entry, then verify the product’s current status and complete label. Confirm the crop, target organism, greenhouse use and user category, and follow the stated dose, safeguards, waiting period and application limit. Older recommendation lists are not a substitute.

When planning a new growing area, treat window access, glazing, working routes and room for air circulation as one connected system. The Classic aluminium greenhouse combines roof ventilation with a clearly structured construction, supporting an accessible, clean and considered greenhouse routine.

Recovery / check rather than hope

The crop recovers when new susceptible tissue stays clean, plants dry reliably after watering and work surfaces remain free of fallen flowers, leaves and fruit.

During the next 72 hours

Check the original infection site and neighbouring plants daily. Remove newly appearing suspect material immediately. Look beneath leaves and into dense crowns, not only at plant parts facing the path.

During the next week

Note when condensation appears and disappears. If it regularly remains into the morning, deliberately change one practical factor: watering time, spacing, air movement or the coordinated combination of heat and ventilation.

For the next growing cycle

Choose crops and varieties suited to the available space, plan a weekly care round and link every harvest or pruning job to cleaning the floor, bench and work surface.

For a clear, accessible growing area, consider the Classic aluminium greenhouse. A consistent, simple routine is usually more valuable than a complicated system that is not followed reliably.

FAQ

Common questions when grey mould appears in a greenhouse.

Can I save a plant affected by Botrytis?

Often yes, provided the infection is small, clearly limited and you act early. Carefully remove affected parts with a margin beyond visibly damaged tissue, clean the surroundings, improve drying and monitor the plant closely. With severe stem infection, multiple centres or widespread sporulation, isolation or disposal can be wiser. Infected tissue itself does not recover.

Is lower humidity enough for prevention?

No. Lower humidity can help, but surface wetness, condensation, stagnant air, faded flowers, wounds, dense foliage and plant debris act together. The key aim is to avoid long periods when susceptible plant surfaces remain cool and wet.

Should I spray grey mould off the plant with water?

No. Washing can spread spores and prolong leaf wetness. Instead, carefully remove and bag affected material, then correct watering and climate management. Use a plant-protection product only after verifying its current authorisation for the crop, target organism, greenhouse use and user category.

Can affected plant material go on a home compost heap?

For visibly fungal or sporulating material, closed disposal through household or organic waste is the more cautious choice where locally available. Home compost heaps do not always reach temperatures evenly enough to destroy plant pathogens reliably. Do not carry infected material openly through the crop or store it in, or immediately beside, the greenhouse.

Why does grey mould appear after a cold night without watering?

When temperatures fall, plant surfaces and glazing can cool to the dew point. Moisture from greenhouse air then condenses on leaves, flowers and stems even though no watering took place. Check inside dense crops in the morning and adjust the balance of watering time, ventilation, air circulation and, where appropriate, moderate warmth.

Sources and further information

Reliable guidance for diagnosis and crop-specific decisions.

Botrytis management depends on plant type, cultivation method, weather and a product’s current authorisation. For decisions in Malta, check the current Maltese register entry and label. The cited German environmental guidance and university resources provide additional context on symptoms, condensation, hygiene, disposal and integrated crop management.

Before nightfall

Remove vulnerable tissue before dusk.

One of the most convincing greenhouse routines is also one of the most effective: leave the crop as dry, well ventilated and free of ageing material as possible, so it cannot become tomorrow’s starting point for grey mould overnight.

Classic aluminium greenhouse

01
Collect spent blooms.
Remove petals and faded flowers before they remain in leaf axils or on fruit.
02
Check damp inner areas.
Look into dense crowns, beneath leaves and along cool glazing – not only from the central path.
03
Create air routes again.
Move touching pots apart, tie in shoots and keep routes clear for air movement and inspection.
04
Carry waste out sealed.
Bag suspect material at the site and do not leave open piles in or beside the greenhouse.