Grey Mould (Botrytis) is a common disease that affects strawberries, raspberries and french beans in Scotland. Here is what it looks like, the conditions it needs, and the controls that actually work.
What does it look like?
Fuzzy grey-brown mould on decaying plant parts; shrivelled buds and flowers that die; small black seed-like structures (sclerotia) on infected material; soft brown decay on fruits such as strawberries; and branch death on cane fruits.
What causes it
High humidity and poor ventilation significantly promote the disease. It thrives as a saprophyte and can infect without wounds, particularly under humid conditions. Overcrowded plants increase risk.
The 'infects without wounds' point matters: it is why removing damaged fruit is not sufficient on its own.
This pest is active year-round under cover: there is no seasonal break.
🌱 Plants at risk
Grey Mould (Botrytis) also affects these crops:
Life cycle
Airborne spores are always present. The disease can occur year-round and may cause latent infections that do not show symptoms immediately.
Why this matters in Scotland
A wet-climate disease that Scottish growers meet twice — outdoors on soft fruit, and under cover where the polytunnel that protects tomatoes from blight creates the humidity botrytis wants.
High humidity and poor ventilation are the drivers. Scotland supplies humidity outdoors, and tomatoes, peppers and chillies are grown under cover almost by necessity in most Scottish gardens, for warmth rather than shelter from rain. Enclosure trades fewer arriving spores for better conditions for anything already inside, since a polytunnel or greenhouse holds humidity even more effectively than open ground does. Ventilation is the practical answer either way, indoors or out.
Controls: what actually works
All the methods below are backed by real evidence, not just repeated folklore.
Chemical control
No fungicides are currently approved for gardeners to use against grey mould.
What actually works: No fungicide will touch grey mould, so ventilation is the real control: improve airflow, avoid overcrowding, and clear dead or dying material promptly, before it becomes the next spore source.
Reduce humidity through improved ventilation; avoid overcrowding plants
Reduce humidity by improving ventilation, and avoid overcrowding plants.
Spacing isn't only about yield: giving plants enough room is itself a disease control, not a separate consideration from it.
Remove dead and dying plant material promptly; dispose of infected parts carefully to prevent spore dispersal
Myths about grey mould (Botrytis)
5 common claims about grey mould (Botrytis), checked: 2 busted1 disputed0 untested2 hold up
“Cutting off and binning affected leaves or fruit stops grey mould spreading”
Removing infected material is worth doing, but it does not stop spread on its own, because the plant is releasing spores into the air the whole time it sits there and again in the act of removing it. Grey mould's spores are airborne and always present in the environment; picking an infected leaf or fruit disturbs the mould and can visibly release a cloud of spores at the moment of removal. Sanitation is a slow-down measure, not a seal.
Our read RHS treats grey mould's spores as constantly airborne and notes they disperse very easily; a US extension guide describing the same fungus records a visible cloud of spores released when infected leaves or flowers are picked, while still recommending removal as part of a wider routine.
What to do: Keep removing dead and infected material promptly as one part of the routine, but pair it with better spacing and ventilation; don't treat a clean-up as having solved the problem.
In Scotland: Under cover, where a polytunnel or greenhouse traps humidity, spores released during removal have nowhere to disperse to and can simply resettle on the next plant along, so ventilation matters as much as the clean-up itself.
2 sources
- RHS: Grey mouldBotrytis cinerea is an ubiquitous fungus whose airborne spores are always present and disperse very easily.
- Clemson HGIC: Gray Mold (Botrytis Blight) on Flowers, Fruits, and VegetablesSanitation is one of the best ways to reduce risk, but a cloud of grayish-white spores may be noticed when infected leaves or flowers are picked.
“Spraying a fungicide is the best way to deal with grey mould”
For a UK amateur gardener this isn't an option worth reaching for, because there is nothing approved to reach for. No fungicide products are currently approved for gardeners to use against grey mould, which makes ventilation, spacing and prompt removal the entire toolkit rather than one option among several.
Our read No fungicides are approved for gardeners to use against grey mould.
What to do: Skip the fungicide aisle for this one and put the effort into airflow, spacing and hygiene instead, since that is the only control available.
In Scotland: Home garden centres sometimes stock general-purpose fungicides that claim broad disease control; none of them carries UK amateur approval for grey mould specifically, so label claims for other diseases shouldn't be read as covering this one.
1 source
- RHS: Grey mouldNo fungicides are approved for use against grey mould by gardeners.
“Grey mould only gets into plants through wounds or damaged tissue, so undamaged plants are safe”
It depends which part of the plant. On leaves and stems, a wound or some other stress is usually needed before the fungus can get a foothold. On flowers and ripening fruit, that protection doesn't apply: the fungus can infect through completely intact tissue, especially once humidity is high. A grower who only checks for nicks and bruises before worrying about grey mould is applying a rule that holds for foliage but not for the flowers and fruit where the disease usually shows up first.
Our read Grey mould normally enters through a wound or infects plants under stress, but it will infect healthy plants as well, especially in humid conditions. On flowers and fruit it infects readily without any wound at all.
What to do: Treat humidity and airflow as the real defence rather than relying on tissue being intact; inspect flowers and ripening fruit even on plants with no visible damage.
1 source
- RHS: Grey mouldGrey mould normally needs a wound or stressed tissue to establish on leaves and stems, but infects flowers and fruit without any wound under humid conditions.
“Grey mould on strawberries, lettuce and tomatoes is really the same disease, just showing up on different crops”
It is one organism, Botrytis cinerea, with an unusually wide host range rather than a family of crop-specific look-alikes. The same fungus is behind the grey fuzz on strawberries, the collapsed stems on lettuce, the ghost-spotting and stem rot on tomatoes, and the die-back on cane fruit. That matters practically: conditions that favour it on one crop favour it on the others growing alongside it, and a bad infection on one susceptible plant is a spore source for its neighbours regardless of species.
Our read Botrytis cinerea has a very wide host range, unlike related Botrytis species that are limited to single hosts such as snowdrops or onions. Crops it affects include soft fruit, beans, cucumber, courgettes, lettuce and tomatoes, and its susceptible hosts span flowers, fruit and vegetables, from begonias to beans.
What to do: Manage grey mould at the bed or polytunnel level rather than per crop: spacing and ventilation improvements benefit every susceptible plant nearby, not just the one showing symptoms.
2 sources
- RHS: Grey mouldBotrytis cinerea has a very wide host range, unlike related Botrytis species restricted to single hosts, and affects soft fruit, beans, courgettes, lettuce and tomatoes among others.
- Clemson HGIC: Gray Mold (Botrytis Blight) on Flowers, Fruits, and VegetablesGray mold caused by Botrytis cinerea affects a wide range of flowers, fruits and vegetables including strawberries, grapes, beans and tomatoes.
“Watering over the leaves and flowers, rather than at the base, makes grey mould worse”
Wetting foliage and flowers gives the fungus two things it needs: standing moisture to germinateA seed sprouting: breaking dormancy and putting out its first root and shoot, given the right warmth and moisture. Full definition → spores in, and splashes that carry spores from an infected leaf to a healthy one. This sits alongside humidity and overcrowding as one of the practical, controllable drivers of infection, distinct from general air humidity, which a gardener can't easily change but watering method they can.
Our read Avoid overhead watering, because the disease spreads easily in splashing water. High humidity and poor ventilation are the main drivers, which fits with wet foliage adding to the risk rather than being a separate issue.
What to do: Water at the base of the plant, ideally in the morning so any splash that does occur has the day to dry off, rather than overhead or in the evening.
2 sources
- Clemson HGIC: Gray Mold (Botrytis Blight) on Flowers, Fruits, and VegetablesAvoid overhead watering and wetting plants, as the fungus is easily spread by splashing water and wind.
- RHS: Grey mouldHigh humidity and poor ventilation are the main drivers of grey mould, and overcrowded plants are at greater risk.
Frequently asked questions
What should I do first if I find grey mould (botrytis) in my garden?
Start with reduce humidity through improved ventilation; avoid overcrowding plants. After that, remove dead and dying plant material promptly; dispose of infected parts carefully to prevent spore dispersal. Work through the rest in order of how well-evidenced they are if the first two aren’t enough on their own.
Is there a spray that works?
No. There are no amateur chemical treatments available for grey mould (botrytis). The controls that work are cultural: the measures listed above.
How much of this advice is actually proven?
Every control listed above is evidence-based, not just repeated folklore. None of it is a guess.
Sources
1 source, recorded with what each was used for
- RHS1: organism and ubiquity, symptoms including sclerotia and soft brown fruit decay, humidity/ventilation/overcrowding drivers, infection without wounds, year-round occurrence and latent infection, no approved fungicides, cultural measures