Sick rose: identify the problem by its symptoms

Diagnosis at a glance

Look at the symptom's position, then run a finger over it. A black spot that does not rub off points to a fungus within the leaf; a white coating that powders your fingers suggests powdery mildew; orange dust underneath indicates rust; a sticky leaf suggests a sap-feeding insect. Roses (Rosa) have only a few common enemies, but these can look similar from a distance.

What you see	Likely cause	Read more
Black or purplish spots with fringed edges; leaves yellow, then fall	Black spot disease	Black spot
White powder on young leaves, stems, and buds	Powdery mildew	Powdery mildew
Yellow spots above, orange pustules below, turning black in late summer	Rust	Rust
Buds stay closed, petals stick together, then gray fuzz develops	Flower balling, gray mold	Buds
Green or pink colonies on buds, sticky leaves	Aphids	Insects
Leaflets rolled into tubes, spring to early summer	Leaf-rolling sawfly	Insects
Leaves mottled with pale speckles, white shed skins beneath	Rose leafhopper	Insects
Stem tips turn brown and dry out	Shoot dieback	Prevention

A yellow leaf without spots or insects needs a different assessment: watering, soil, and nutrient deficiency.

Quand le feuillage jaunit sans la moindre tache : yellow rose leaves ont leurs propres causes, du sol calcaire à l'eau qui stagne.

A symptom that fits none of these rows? Photograph the leaf: Floralens identifies the problem and suggests an appropriate action.

Black spot: the most serious disease

Purplish-black spots spreading quickly across the upper leaf surface, followed by yellowing and leaf drop, indicate black spot, called marsonia in French (Diplocarpon rosae). The RHS considers it the most serious rose disease: a badly affected plant loses almost all its leaves and much of its vigor. Small, black, scabby lesions can also mark young stems¹.

The life cycle explains the precautions. The fungus overwinters on fallen leaves and in young stems. In spring, rain splashes spores onto lower leaves: they germinate and enter the leaf within 48 hours, with new fruiting structures 9 to 15 days later. Disease then persists from May to September in the French source climate, depending on weather². Jardiner Autrement sees the first spots in early summer in rainy weather³. Elsewhere, monitor local leaf growth, rain, and temperature rather than those months alone.

Steps that slow the disease:

1. Collect fallen leaves in fall, or bury them under mulchA layer of organic or mineral material spread around plants to retain soil moisture and suppress weeds. at least 5 cm (2 in) deep, applied from November to February in the RHS's UK winter calendar¹. Follow the equivalent dormant season locally.
2. Prune out stem lesions in spring, before leaves emerge¹.
3. Water at the base and avoid evening watering that leaves foliage wet overnight³.
4. Remove the first affected leaves as soon as symptoms appear³.

The RHS warns that these steps delay disease more than prevent it: spores also arrive in wind-driven rain¹. Variety resistance needs the same caution: advertised resistance rarely lasts more than a few years as new strains emerge, while species rosesWild species of Rosa and their older forms, as distinct from modern garden-center hybrids. are little affected¹. Some reassurance: the disease rarely kills its host and its effect remains mainly cosmetic².

See symptom photographs under large black patches.

Powdery mildew: a white coating

White powder on leaves and young shoots, curled leaves, and buds that will not open indicate powdery mildew (Podosphaera pannosa). The coating also spreads over stems, often around prickles, flower stalks, and petals⁴.

It behaves differently from the other diseases. Wet leaves are not required: powdery mildew benefits from humid, still air and periodically dry soil. Poorly ventilated climbers pressed against walls suffer most⁴. Clemson gives ideal conditions of 21 to 27 °C (70 to 81 °F), with humid nights and dry days; a film of water on a leaf can actually hinder infection⁵.

The sources disagree about season. The RHS calls it a disease of dry summers⁴, while Jardiner Autrement mainly sees it in spring and fall, considering summer too hot⁶. Their shared conditions matter more than a universal calendar: cool, humid nights followed by warm days.

Recommended steps, in order:

• Full sun and airflow: give the plant space, prune to open its center, and avoid crowding⁴.
• Keep soil from drying out: water regularly during dry spells and mulch⁴.
• Avoid excess nitrogen, which produces tender, vulnerable shoots⁴.
• Cut affected shoots at the first spots: Jardiner Autrement stresses this timing⁶.

See treating powdery mildew for the steps.

Rust: orange pustules under leaves

Angular yellow spots above and orange, powdery pustules below indicate rust (Phragmidium mucronatum). The pustules brown, then turn black in late summer, and heavy infection causes leaf drop⁷⁸. In spring, the first patches sometimes appear on young stems, distorted and covered in orange spores⁸.

The fungus needs liquid water on the leaf for at least 2 hours and temperatures of 18 to 20 °C (64 to 68 °F)⁷. It overwinters in fallen leaves and young shoots.

The RHS considers it the least serious of the three common diseases, with most infections too light to justify treatment⁸. Cut out spring infections as soon as you see them, collect leaves in fall, and replace the variety if the same plant develops rust year after year⁸. See treating rust.

Buds that rot without opening

Buds that stay closed, with outer petals stuck into a papery shell, then turn moldy are showing flower balling. The RHS explains the weather sequence: cool rain saturates petals, then sun dries and sticks them together. Double-flowered roses with thin petals are most vulnerable, especially during wet, shaded spring and summer conditions⁹.

The real danger follows: a rotten bud develops gray moldA fungus, Botrytis cinerea, forming gray fuzz on flowers, buds, and wounded tissue in cool, damp weather., which spreads to other flowers. Remove balled buds promptly⁹. Clemson places botrytis activity at 17 to 22 °C (63 to 72 °F) in wet weather and recommends discarding spent flowers and fallen leaves⁵.

No product corrects this disorder: use an open site, pruning that improves airflow, watering directed at soil, and replace a variety affected every year⁹. See gray mold.

Aphids, sawflies, and leafhoppers on roses

Rose aphids (Macrosiphum rosae) are green or pink and reach 3.5 mm (0.14 in). They crowd buds and tender shoots from March to August in the RHS's UK calendar, peaking in early summer, and excrete honeydewA sweet, sticky liquid excreted by sap-feeding insects, on which sooty mold grows. that supports black sooty mold¹⁰. The RHS recommends tolerating small colonies, squashing patches between your fingers, and allowing lady beetles, hoverflies, and small parasitic wasps to reduce numbers in summer. Aphids often begin before their predators in spring: inspect roses early¹⁰. Elsewhere, use local growth and observed activity to time checks. See removing aphids and cleaning honeydew.

Leaf-rolling sawfly rolls leaflets into tubes from late April to early June in the RHS's UK climate, sheltering its pale green larva. Roses almost always recover: remove rolled leaves only when there are few, because removing many harms the rose more than the insect¹¹. Monitor the equivalent local spring growth stage elsewhere. See sawflies.

Rose leafhoppers mottle upper leaf surfaces with pale speckles, especially in hot, dry weather, from May to September in the RHS's UK climate. Turn a leaf over: white nymphal shed skins remain underneath. Rose vigor rarely suffers, and the RHS recommends tolerance¹². Finer mottling with tiny mites and sometimes silky webbing instead suggests spider mites, active from March to October in that source climate during hot, dry weather¹³. Elsewhere, follow local conditions and observed activity. See leafhoppers and spider mites.

When to watch for problems

Each problem has its season in the source climates: aphids and sawflies in spring, black spot and leafhoppers through summer, powdery mildew and rust throughout growth. The calendar below brings together the sources' published periods, month by month where supplied. These are source-climate examples; local warmth, rainfall, and growth determine actual monitoring.

As local spring growth begins, turn over a few leaves each week; during summer growth, check foliage after rain; in fall, collect fallen leaves before winter.

Care without pesticides: the French source's legal context

The French source states that synthetic chemical plant-protection products have been prohibited for amateur gardeners in France since January 1, 2019¹⁴. It lists biocontrolPlant-protection methods using natural mechanisms, including beneficial insects, naturally derived substances, and pheromones., low-risk products, and products permitted in organic farming as remaining allowed there¹⁴. Its packaging instruction is to look for “Emploi autorisé au jardin”, meaning authorized for garden use³. This is the source's France-specific account, not your local law. The RHS goes further, recommending no fungicide at all for rose diseases¹.

Homemade preparations deserve the same caution. The Société française des roses notes that seaweed, nettle, garlic, or comfrey decoctions and infusions are supposed to strengthen rose defenses, but this has yet to be demonstrated¹⁵. Jardiner Autrement reaches the same conclusion for nettle or horsetail liquids against powdery mildew⁶.

Protection starts before local spring growth:

• A cleanup pruning in November or December in the SFR's French calendar removes about one-third of shoot length, including diseased leaves that could reinfect the rose in spring¹⁵. Elsewhere, match this to local dormancy.
• Cut dead wood as soon as it appears, cleanly above a healthy bud¹⁶. Clemson gives 1 part bleach to 9 parts water for blade disinfection⁵; this is its stated recipe without a proven safety or effectiveness guarantee here.
• Space plants apart so foliage dries quickly after rain⁷.
• Do not plant a new rose where an old one grew: the Société française des roses considers the site unsuitable for 7 to 8 years¹⁵.

Le meilleur moment pour éliminer le bois malade est aussi celui de la taille : pruning a rose se fait en fin d'hiver pour la plupart des types.

Une eau versée au pied, le matin, protège mieux qu'un traitement : watering a rose sans mouiller les feuilles limite les trois champignons.

Add your rose: Floralens reminds you when to watch for black spot and aphids, season by season (Pro mode). Get reminders

Frequently asked questions

How do I treat rose diseases?

Identify the disease first: fringed black spots, powdery mildew's white coating, or rust's orange pustules. Remove affected leaves at the first symptoms, water at the base, and collect fallen leaves in fall³. The French source states that since 2019 only biocontrol, low-risk, or organic-approved products remain permitted for amateur garden use in France¹⁴. That statement is specific to France.

What disease causes black spots on rose leaves?

Black spot, called marsonia in French, caused by Diplocarpon rosae. Purplish-black spots spread quickly, leaves yellow and fall, and small black lesions can also mark young stems¹. It persists from May to September in the French source climate, depending on weather². Monitor the corresponding local wet growing conditions elsewhere.

How do I get rid of powdery mildew on a rose?

Cut white-coated shoots at the first spots⁶, then address the causes: crowding or a plant pressed against a wall, periodically dry soil, or excessive nitrogen⁴. A rose in full sun with good airflow and regular watering during dry spells is much less affected.

Does black soap work against rose diseases?

No authoritative source cited here recommends it against fungi. The Société française des roses says natural preparations' effect on rose defenses remains unproven¹⁵. For aphids, the RHS first recommends tolerating small colonies, squashing them by hand, and letting beneficial insects act¹⁰.

Should I remove diseased rose leaves?

Yes, when there are only a few: removing the first spotted leaves slows black spot³, and cutting white-coated shoots slows powdery mildew⁶. Also collect and destroy fallen leaves, where fungi overwinter¹.