Key takeaways
- Powdery mildew loves warm days and plants that are dry at the roots
- Water at the base in the morning and mulch to keep soil evenly moist
- Give plants room and prune to an open shape so air can move
- Each plant gets its own mildew, so it won't jump from roses to courgettes
- Home-made milk, bicarbonate and garlic sprays aren't authorised in the UK; use only an approved product
- Resistant rose, apple and pea varieties save a lot of bother
Powdery mildew is the most common fungus problem in UK gardens. It’s that white, floury coating on rose leaves, courgettes and apple shoots. The good news is that each plant gets its own type of mildew, so the one on your roses can’t spread to your courgettes.
Unlike most fungal diseases, it doesn’t need wet leaves. It loves warm days and plants that are dry at the roots, which is why it’s worst from May to September. Get the watering and spacing right and you can keep it in check without spraying every week.
How to spot powdery mildew
It’s easy to recognise. White or greyish powdery patches appear on the tops of leaves, then spread to stems, buds and sometimes fruit. It looks as if someone has dusted the plant with flour.
As it spreads, leaves may curl, turn yellow and drop early. Young shoots twist out of shape. On apples and courgettes, mildew can leave the skin rough and cracked. Flower buds may not open, or open misshapen.
That white dust is the fungus itself, and it’s full of spores. They blow onto nearby leaves and start new patches within a few days in warm weather.
Powdery mildew looks like a dusting of flour on top of the leaf. It usually starts on the oldest courgette leaves and climbs from there.
How is powdery mildew different from downy mildew?
Powdery mildew sits on top of the leaf as a dry white dust you can rub off with a finger. Downy mildew grows underneath as a grey or purplish fuzz, with yellow or brown patches on top.
They like opposite weather. Downy mildew needs wet leaves and cool, damp spells, so it’s common in wet springs and autumns. Powdery mildew likes dry roots and warm days. This matters because the fixes differ. Watering a dry plant helps with powdery mildew but can make downy mildew worse. Downy mildew can also kill lettuces and brassica seedlings quickly. Our guide to lettuce downy mildew has the details.
Gardener’s tip: Check under the leaves as well as on top. On some plants, especially brassicas, mildew can show up more on the underside. The earlier you spot it, the easier it is to sort.
Which plants get it most
Roses, courgettes, cucumbers, apples, peas, gooseberries and grapes are hit most often. Each has its own mildew, so here’s when to keep an eye out.
| Plant | When to watch | How badly it’s hit |
|---|---|---|
| Roses | June to September | Badly |
| Courgettes and squash | July to September | Very badly |
| Apples | May to August | Badly |
| Peas | June to August | Quite badly |
| Cucumbers | June to September | Very badly |
| Gooseberries | May to July | Badly |
| Grapes | June to September | Very badly |
| Oak trees | June to October | Mildly |
| Asters and Michaelmas daisies | July to October | Moderately |
| Delphiniums | June to August | Moderately |
Roses
Powdery mildew is one of the big three rose diseases, along with black spot and rust. Hybrid teas and floribundas are most prone. Climbers on sunny walls suffer badly, because the wall throws back heat and the soil at its foot stays dry. New roses are more at risk than settled ones. Our guide to how to prune roses helps keep them healthy.
Roses on warm walls suffer most, because the soil at the foot of the wall stays dry. A good soak and a thick mulch help more than you’d think.
Courgettes and cucumbers
These are mildew magnets. It usually starts on the oldest leaves in mid to late summer and climbs fast. Badly hit courgettes stop cropping weeks early. Both outdoor and greenhouse cucumbers and courgettes get it, but greenhouse plants suffer more from still air.
Peas
Mildew on peas is worst on late sowings. It coats the pods and cuts your crop. Peas sown in March and April usually dodge the worst of it, because they’re ready before mildew season peaks.
Apples
Apple mildew hides over winter in infected buds. In spring, those buds open into shoots already coated in white. These shoots then spread spores to healthy leaves all summer. Left alone, trees give smaller fruit and poorer crops.
Mildewed apple shoots stand out in spring as narrow, silvery leaves. Snip them out early and bin them before they spread spores all summer.
What causes powdery mildew?
Spores blow in on the breeze, but they take hold mainly on plants that are short of water at the roots. Dry soil with humid air around the leaves is the classic recipe.
The RHS powdery mildew advice explains that plants that keep drying out are more prone to it. That’s why it’s worst on:
- Climbing roses and wall-trained fruit, where the soil at the foot of the wall stays dry
- Courgettes and squash in late summer, once watering slips
- Plants in pots, hanging baskets and raised beds that dry out fast
- Crowded beds and greenhouses where still, humid air hangs around the leaves
Soft, sappy growth from too much high-nitrogen feed adds to the risk. Keeping the soil evenly moist and mulched does more than any spray.
How mildew gets through the year
Knowing where it hides helps you get ahead of it.
Autumn and winter: it sits out the cold in infected buds, especially on roses and apples, and on fallen leaves. In mild winters it can carry on growing on evergreens and in greenhouses.
Spring: as it warms up, spores start flying. Infected apple buds open into mildewed shoots. New rose growth picks up spores from the wind.
Summer: the peak. Spores spread fast in warm weather, and humid nights followed by warm, dry days suit it perfectly.
Late summer and autumn: it heads back into buds and fallen leaves for winter. Clearing up fallen leaves breaks the cycle.
Month-by-month mildew care
The key times are winter for pruning, summer for keeping a close eye out, and autumn for clearing up.
| Month | Risk | What to do |
|---|---|---|
| January to February | None | Prune roses to an open shape and remove crossing branches |
| March | Low | Check apple buds for mildewed shoots and cut them out |
| April | Rising | Mulch around roses, fruit and veg beds while the soil is moist |
| May | Medium | Check courgette and cucumber plants before planting out. Water in dry spells |
| June | High | Water at the roots in the morning. Pick off infected leaves |
| July | Very high | Check courgettes and cucumbers often. Keep watering steady |
| August | Very high | Remove badly hit lower leaves on courgettes |
| September | Medium | Clear spent courgette and pea plants |
| October | Low | Clear up fallen rose and apple leaves and bin them |
| November to December | None | Plan resistant varieties for next year |
Simple ways to prevent it
Good spacing, careful watering, open pruning and sensible feeding prevent most powdery mildew without any spraying. The RHS puts these first, ahead of sprays.
Give plants room
Crowded plants trap still, humid air, and mildew loves that. Space roses about 90cm apart. Give courgettes 90-120cm. Train climbers on open supports rather than flat against a wall. Thin crowded gooseberry bushes in winter.
A breeze across the leaves makes life harder for mildew. Avoid putting prone plants in sheltered corners where the air sits still.
Give courgettes a good metre each way so air can move between them. A thick mulch keeps the roots moist, which mildew hates.
Water the right way
Water at the base, never over the top. Wet leaves don’t cause powdery mildew, but evening sprinkling makes the air around plants humid all night, which it likes.
Water in the morning so any splashes dry quickly. Drip lines and soaker hoses are ideal. A 5-8cm mulch of compost or bark keeps the soil moist for longer. Our guide to water-efficient gardening has more ideas.
Water at the roots in the morning, not over the leaves at night. Steady moisture at the roots is the best defence against powdery mildew.
Prune to an open centre
On roses, cut to an outward-facing bud to make an open, vase shape. Take out branches growing into the middle. Do the same on apple trees, so air and light can get in.
Cut off any mildewed shoots. Don’t compost them, as most home heaps don’t get hot enough to kill the spores. Put them in the bin instead.
An open centre lets the breeze through the middle of the bush. Cut to outward-facing buds and take out anything crossing inwards.
Go easy on nitrogen
High-nitrogen feeds push out soft, lush growth that mildew loves. Use a balanced feed. Stop feeding roses after mid-July, as late soft growth is prone to both mildew and frost.
Organic options and the rules on sprays
Prevention is your best organic tool. If you do want a spray, the UK rule is simple: only ready-made products approved for amateur use can legally be sprayed to control a plant disease.
Milk spray
Milk is the best-known home remedy, and you’ll see it all over the internet. But milk isn’t an authorised plant protection product in the UK, so don’t mix or spray it to control mildew.
Potassium bicarbonate
Potassium bicarbonate is the active ingredient in some ready-made fungicides. Don’t mix your own from bicarbonate powder, as home-made mixes aren’t authorised. Use only an approved ready-made product whose label lists powdery mildew and your plant, and follow the label exactly. Baking soda (sodium bicarbonate) isn’t an authorised fungicide either.
Sulphur
Sulphur is a long-standing fungicide that stops spores taking hold on leaves. If you find an approved product, use it before mildew takes hold and follow the label exactly. It can scorch leaves in hot weather, and some gooseberry varieties don’t like sulphur at all, so check the label first.
Are home-made mildew sprays legal in the UK?
No. Home-made mixes such as milk, bicarbonate or garlic sprays aren’t authorised plant protection products. Only products approved for amateur use should be used to control a plant disease.
The HSE guidance for home gardeners points out that household mixes used this way aren’t without risk. The RHS doesn’t recommend them either, as they’re unregulated and untested.
The safe route is a ready-made product whose label lists powdery mildew and your crop. Buy only what you’ll use within a year, and check older bottles against the HSE database, as approvals do expire.
Garlic spray
Garlic sprays pop up online a lot, but home-made garlic mixes aren’t authorised in the UK, so don’t use them on mildew or pests. Our organic pest control guide covers legal approaches you can use instead.
Shop-bought fungicides
If prevention isn’t enough, there are fungicides for home gardeners that list powdery mildew on the label. Which ones are approved changes over time, so check what’s on the shelf against the HSE database.
Picking a product
Look for a label that names powdery mildew and the exact plant you want to spray. Some are only for ornamentals like roses, not for fruit and veg. If you’re spraying something you’ll eat, check the harvest interval on the label.
Using it safely
- Read the label. Follow its dilution, how often to spray and the harvest interval for edible crops.
- Spray early in the morning or late in the evening, when bees are less busy.
- Cover all the leaves, including underneath.
- Don’t spray if rain is due within a few hours.
- Wear gloves and eye protection when mixing and spraying.
- Never go over the maximum number of sprays the label allows.
Resistant varieties
Choosing a resistant variety is the easiest fix of all. Breeders have produced plenty that shrug off mildew.
Mildew-resistant roses
- ‘Olivia Rose Austin’ (David Austin): very healthy, repeat flowering
- ‘Desdemona’ (David Austin): good resistance, white cupped blooms
- ‘Roald Dahl’ (David Austin): healthy, apricot flowers
- ‘Lady of Shalott’ (David Austin): vigorous and healthy
- ‘The Lark Ascending’ (David Austin): single flowers, very healthy
- ‘Tottering-by-Gently’ (David Austin): healthy, soft yellow flowers
When you shop for new roses, look for ones described as having good disease resistance.
Mildew-resistant courgettes
- ‘Tosca’ F1: compact plants with good mildew tolerance, handy for smaller spaces
Mildew-resistant apples
- ‘Discovery’: early eating apple, good resistance
- ‘Sunset’: Cox-like flavour, fairly resistant
- ‘Red Falstaff’: late eating apple, good disease resistance
- ‘Scrumptious’: self-fertile and reliable
Mildew-resistant peas
- ‘Kelvedon Wonder’: classic, with good tolerance
- ‘Ambassador’: a later pea with good resistance
- ‘Avola’: quick early pea that’s ready before mildew season
Common mistakes
Waiting until it’s everywhere
By the time you see white patches, it’s been there a few days. Keep watering steady from late spring and check prone plants often, so you can act at the first patch.
Sprinkling in the evening
Watering roses with a sprinkler at 8pm keeps the leaves in damp air all night. Water at the base in the morning instead.
Composting infected leaves
Most home compost heaps don’t get hot enough to kill mildew spores. Composting infected leaves just brings the problem back next year. Bin them instead.
Leaving the first infected leaves
A few mildewed leaves can spread spores all over the plant and its neighbours. Pick them off as soon as you see them and bin them.
Planting prone varieties in sheltered spots
A warm, sheltered south-facing corner looks perfect for roses, but still air and reflected heat make it a mildew hotspot. If the air doesn’t move much, choose a resistant variety or a different plant. Our guide to tomato blight prevention uses similar ideas for another common disease.
Next, read our guide to organic pest control for more ways to keep your garden healthy without chemicals.
Not every leaf mark is a fungus, so compare yours with oedema on plant leaves.
Frequently asked questions
Can powdery mildew spread to other types of plants?
No, each type of plant gets its own mildew. The one on your roses can’t infect your courgettes or apples. But each plant that’s prone to it can pick up its own mildew from spores blowing in. There’s no need to keep roses away from the veg patch.
Does powdery mildew live in the soil?
No, it doesn’t live in the soil. It spends the winter in infected buds and shoots, and on fallen leaves. Clearing up infected leaves in autumn means fewer spores next spring. There’s no need to replace or treat the soil.
Will powdery mildew kill my plants?
Rarely, at least not established plants. It weakens them, so they grow less and give you smaller crops. Bad, repeated attacks can finish off seedlings and young plants. Acting early stops lasting damage in most cases.
Is it safe to eat vegetables with powdery mildew?
Yes, they’re safe to eat. Give them a good wash and cut away any badly marked skin. Courgettes, cucumbers and peas with a light dusting of mildew are fine to eat.
When is the best time to spray for powdery mildew?
Early morning or late evening, when bees are less busy. Start at the first sign of white patches, not once it’s everywhere. Only use a ready-made product whose label lists powdery mildew and your plant. Follow the label for how often to spray.
Does neem oil work on powdery mildew?
Neem oil isn’t an authorised fungicide for UK gardens. Products on sale are usually labelled as leaf shines or plant tonics, not pesticides. For a legal option, use a fungicide listed for home garden use on the HSE database, or rely on spacing, watering and resistant varieties.
How do I prevent powdery mildew on roses?
Give them room and keep their roots moist. Space bushes about 90cm apart and water at the base, never overhead. Prune to an open centre in late winter. Choose resistant varieties. Clear up fallen leaves in autumn and bin them rather than composting.
Our team produces practical UK gardening guidance from source research, contributor records and established horticultural practice. Editorial standards are overseen by Matt W.
