Powdery mildew on roses is the white powder that coats the young leaves, buds, and shoot tips in spring and summer, curling the leaves, stunting the growth, and distorting the flowers. It starts as small white spots on the youngest leaves, spreads into a coating that covers the leaf, and then moves to the buds, which may fail to open or open into small, distorted flowers. A rose that is badly hit looks dusty and tired, and it flowers poorly all season. It is the second most common rose disease after black spot, and it is the one that most often affects roses in dry climates, because, unlike black spot, it does not need wet leaves.

The fungus is Podosphaera pannosa, and it is a specialist that attacks roses and almost nothing else. It needs warm days, cool nights, and high humidity, with dry leaves — the opposite of black spot — which is why the two diseases often appear in different weather and why a rose can have one without the other. It grows on the surface of the leaf, feeding on the living tissue underneath, and it is worst on young, soft growth in spring and in autumn, when the days are warm and the nights are cool and damp. The control is about airflow, spacing, resistant varieties, and removing infected growth early, and a rose that is grown with sun and air will often stay nearly clean without any spraying.

What powdery mildew on roses looks like: symptoms

  • White powdery coating: a white, powdery coating on the young leaves, buds, and shoot tips, which starts as small spots and spreads to cover the whole leaf.
  • Curled, distorted leaves: the leaves under the coating curl, pucker, and distort, and they may turn reddish or purple before they yellow and drop.
  • Distorted buds and flowers: buds may fail to open, or open into small, distorted, poorly coloured flowers, and the flower stems may be coated and stunted.
  • Stunted shoots: young shoots that are coated grow slowly and stay short, with small, distorted leaves, and the plant looks generally unthrifty.
  • Yellowing and leaf drop: heavily coated leaves turn yellow and drop, starting with the youngest leaves, which is the opposite of black spot, which starts with the oldest.
  • A dusty-looking bush: the overall look is a rose bush covered in white dust, which is easy to spot from across the garden.

Powdery mildew on roses usually appears in spring, when the young growth is soft and the days are warm and the nights are cool and damp. The first spots show on the youngest leaves and the shoot tips, and the coating spreads over the following weeks, with each new flush of growth becoming coated in turn. In a wet, humid summer the disease can cover the whole bush, and in a dry summer it may stay at a few spots. The disease slows in hot, dry weather and in very cold weather, and it is worst in the mild, humid weather of spring and autumn. A rose that is badly hit in spring will often recover with clean growth in summer, only to be hit again in autumn.

Which plants get powdery mildew on roses

Powdery mildew on roses attacks roses of all kinds — hybrid teas, floribundas, shrub roses, climbers, and old garden roses — though susceptibility varies a lot by variety. Some modern shrub roses are notably resistant, while some older hybrid teas are very prone. The disease is worst on roses in shade, in crowded beds, and in humid climates, and it is particularly bad on young, soft growth in spring. It does not attack other garden plants, so a rose bed with powdery mildew is a rose problem only, and the fungus will not jump to your cucumbers or your grapes.

Conditions that favour powdery mildew on roses

Powdery mildew on roses needs warm days, cool nights, and high humidity, with dry leaves — temperatures in the 70s Fahrenheit with cool nights in the 60s are ideal, and the fungus is inhibited by very hot weather and by rain, which washes the spores off the leaves. It is worst on young, soft growth, in shade, and in crowded beds where the air does not move. The fungus overwinters in the buds and in infected shoots, so a rose that had mildew last year starts the spring with the fungus already in place. Plants that are overfed with nitrogen produce the soft growth the fungus likes best, and plants that are drought-stressed are more badly affected.

How powdery mildew on roses spreads

Powdery mildew on roses spreads by spores that travel on the wind, and it does so very efficiently: a single infected leaf can release enough spores to infect a whole rose bed, and the spores can travel a long way on a breeze. It also spreads by direct contact where leaves touch each other in a crowded bush. The fungus does not need water to spread, which is why it can appear in a dry summer when black spot is absent. It overwinters in the buds and in infected shoots, so the previous year's growth is the usual source of the next year's outbreak.

How to tell it apart from lookalikes

Powdery mildew on roses is sometimes confused with downy mildew, but downy mildew makes purple spots with a greyish growth on the leaf undersides, while powdery mildew makes a white powder on the upper surfaces and the shoot tips. Spray residue or dust can also look white on leaves, but it wipes off easily and does not spread from leaf to leaf. Black spot makes black spots with fringed edges, not a white powder. If the young leaves and buds are covered in a white powder that rubs off on your finger, it is powdery mildew.

Prevention: cultural steps that work

  • Choose resistant varieties when you buy new roses, especially if your climate is humid or if mildew is a recurring problem.
  • Plant roses in full sun with generous spacing and good air movement, and avoid planting them where they are shaded or crowded.
  • Prune for an open centre so air moves through the bush and the leaves dry quickly, and prune out infected shoots in late winter.
  • Water at soil level, in the morning, and avoid wetting the foliage.
  • Feed moderately and avoid heavy nitrogen that pushes soft, vulnerable growth.
  • Remove infected leaves and shoots as soon as you see them, and dispose of them with household waste.
  • In late winter, prune out any shoots that were badly coated last year, since the fungus overwinters in the buds.

Treatment step by step

  1. Pick off coated leaves and shoots as soon as you see them, and dispose of them with household waste. Do this in dry weather so the spores do not puff into the air.
  2. Prune out crowded growth to open the centre of the bush, so air moves through it and the humidity drops.
  3. Water at soil level, in the morning, and avoid wetting the foliage.
  4. If you choose to spray, a fungicide labelled for powdery mildew on roses can protect new growth, but it will not cure leaves that are already coated. Apply it to clean new foliage exactly as the label directs, and start early in the season, before the coating covers the bush.
  5. Feed the rose moderately after the worst of the disease has passed so it can replace its leaves, but do not overfeed with nitrogen.
  6. Keep up the cleanup through the season — a few minutes of picking coated shoots each week does more than a single big effort in August.
  7. In late winter, prune out the shoots that were infected last year, so the bush starts the spring clean.

What recovery looks like

Recovery from powdery mildew on roses is usually quick once the weather warms and dries and the infected growth is removed: new leaves and buds should come through clean, and the bush will start to fill in and flower again. The coated leaves will not heal — they will yellow and drop — but a rose grows fast and can replace them quickly. The recovery is fastest in hot, dry, sunny weather, which inhibits the fungus, and slowest in cool, humid weather. A rose that keeps its new growth clean for two weeks after the outbreak is on the way back, even if its young shoots are still white. Full recovery is a next-season matter: a bush that is pruned in late winter and given sun and air in spring will often stay nearly clean the following year.

When a plant is beyond saving

A rose is rarely beyond saving from powdery mildew alone, because the disease attacks the leaves and buds, not the roots or the crown. A bush is in serious trouble only when it has been badly coated several years running, when its growth is weak and its flowering poor, and when it fails to leaf out properly in spring. Even then, a hard prune in late winter, good feeding, and a season of clean culture can often revive it. The time to replace a rose is when it is a very susceptible variety in a humid, shady spot where mildew returns every year no matter what you do — in that case, a resistant variety in a sunnier position is the better investment.

Frequently asked questions

Will powdery mildew kill my rose?

Almost never on its own, but repeated severe infection weakens the plant over several seasons, reduces flowering, and makes it more vulnerable to winter cold and other problems. It is worth controlling even though it is rarely fatal.

Can I compost rose leaves with powdery mildew?

No. Home compost rarely gets hot enough to kill the fungus, so composting infected leaves returns the disease to the garden. Bag the leaves and put them with household waste.

Why do my roses get powdery mildew but my neighbour's do not?

Variety, position, and pruning make the difference. A resistant variety in full sun with an open centre can stay clean while a susceptible variety in shade, crowded and unpruned, is covered in white powder.

Should I spray for powdery mildew on roses?

Spraying can help protect new growth on a susceptible variety, but it is optional if you are willing to accept some leaf loss, and it never cures leaves that are already coated. Good culture — sun, air, pruning, resistant varieties — is the foundation, and any spray is an addition to it, used as its label directs.

When is powdery mildew worst on roses?

In spring and autumn, when the days are warm and the nights are cool and damp and the young growth is soft. Hot, dry summer weather usually slows it down, and a rose that is badly hit in spring will often recover with clean growth in summer — and check your local extension service for the varieties that resist mildew best in your area.

Getting help and going further

If you are unsure which disease you are dealing with, take clear photos of the symptoms and check your local extension service — they can confirm a diagnosis from a sample and advise on the varieties and the timing that work best in your area. You can also try our plant disease checker to narrow down the problem, and browse the guides hub for related disease guides. For growing advice, see growing roses. For growing advice, see zone 6 roses. For growing advice, see growing fiddle-leaf fig. Related guides: black spot roses, powdery mildew on squash, rust disease plants. Whenever you remove diseased material, dispose of it with household waste — do not compost diseased material, since home compost rarely gets hot enough to kill the organisms that cause these diseases. Good record-keeping helps too: note the date, the weather, and the variety when a problem first appears, so you can spot the pattern next year and act earlier.