Hollyhocks are among the most recognisable plants in the British cottage garden, producing towering flower spires along fences and walls from midsummer onward. When the lower leaves begin to curl, yellow, and drop while the plant is still in flower, the culprit is almost always hollyhock rust, a fungal disease so widespread in the UK that most hollyhocks carry it to some degree every season. Aphids, capsid bugs, hollyhock weevil, powdery mildew, and waterlogging can also cause curling and distortion, but rust is the starting point for any diagnosis on a British garden plant.
Hollyhock rust: the dominant problem in UK gardens
Hollyhock rust is caused by the fungus Phragmidium malvacearum, a specialist pathogen that infects plants in the mallow family, with hollyhocks as its primary host in UK gardens. It is the single most destructive disease hollyhocks face and is so prevalent in the UK that experienced gardeners treat it as an almost inevitable part of growing the plant rather than an occasional problem. The infection begins on the lower leaves, working upward through the plant as the season progresses, and in a bad year can defoliate hollyhocks entirely by late summer.
The symptoms are distinctive once you know what to look for. On the upper surface of the leaf, small orange-yellow spots or pustules appear, often surrounded by a pale halo. These spots are easy to overlook at first, but turning the leaf over reveals the characteristic underside: clusters of orange-brown powdery pustules arranged in rings or scattered across the surface. Affected leaves curl upward as the fungal growth disrupts normal leaf tissue, and severely infected leaves turn brown and drop prematurely. The rust spreads rapidly through summer, carried by wind and splashing rain, and plants growing close together in a border share the infection quickly.
Alcea rugosa, the Russian hollyhock, is sometimes cited as more resistant to rust than Alcea rosea, and in trials it does show lower infection rates. The Halo series of hollyhocks, bred partly for ornamental garden use, also shows better rust tolerance than heritage cultivars. In practice, neither is fully immune in UK conditions, but they can make a meaningful difference in gardens where rust pressure is consistently high.
Treating and managing hollyhock rust
No fungicide cures rust once it is established in leaf tissue. The goal of treatment is to protect healthy tissue from further infection and to slow the spread through the plant. Apply a copper-based fungicide such as Bordeaux mixture or copper oxychloride, or a systemic myclobutanil-based product, from May onward, before symptoms appear. Repeat every two to three weeks through the growing season, coating both the upper and lower leaf surfaces thoroughly so that newly landed spores cannot germinate. Remove affected leaves as soon as symptoms appear, taking them away from the garden rather than letting them fall and releasing spores into the soil. In autumn, clear and dispose of all fallen hollyhock foliage, stems, and debris in the bin or by burning: the rust overwinters on dead plant material and the spring inoculum the following year comes directly from the previous season's clearance failures. Do not compost hollyhock rust material.
Aphids: downward curl on young shoots and stems
Two aphid species are most commonly found on hollyhocks in UK gardens. The black bean aphid (Aphis fabae) is a familiar garden pest with a wide host range, forming dense black colonies on stems and the undersides of young leaves. The hollyhock aphid (Aphis althaeae) is a more specialist species, grey-green to grey in colour, that targets mallow-family plants including hollyhocks, sidalcea, and mallows grown in borders.
Aphid feeding on hollyhocks causes a distinctly different leaf response from rust. Where rust produces upward curl, aphids cause the leaves to roll downward and inward, particularly on the youngest growth at shoot tips and along new stems. The rolling partly shelters the colony from predators and rainfall. Sticky honeydew coats the foliage below the feeding sites, and sooty mould, a black superficial fungal growth, often follows. Heavy aphid infestations on hollyhocks weaken new growth, reduce flower production, and can distort the soft tissues of young stems and buds before they harden.
Natural predators, including ladybirds, hoverfly larvae, and parasitoid wasps, arrive in UK gardens from May onward and bring aphid colonies under control through the summer without any intervention needed in most years. On plants that are badly affected early in the season, rub colonies off by hand on a cool morning when insects are least active, or dislodge them with a firm jet of water directed at the shoot tips and leaf undersides. Insecticidal soap applied directly to the colonies is effective for heavier infestations. Avoid broad-spectrum insecticides, which kill the natural predators that would otherwise limit aphid populations through the rest of the season.
Other causes of hollyhock leaf distortion
Capsid bugs, particularly Lygus rugulipennis (the common green capsid), cause irregular pitting and small ragged holes in young expanding leaves as their toxic saliva breaks down plant tissue around the feeding site. The damage only becomes visible as the leaf expands after the insect has moved on, which makes the pest difficult to catch. Young leaves look tatty, distorted, and puckered rather than smoothly curled, with a pattern of small holes and brown-edged pits scattered across the surface. Capsid damage is most noticeable from May to July on the youngest leaves near shoot tips.
The hollyhock weevil (Rhopalapion longirostre) is a small, elongated weevil that lays its eggs inside hollyhock flower buds. The larvae feed inside the developing bud, causing it to fail to open or to emerge distorted and holed. The adult weevils also feed on the foliage and young stems. Damage from the hollyhock weevil is more commonly seen on buds than on leaves, but it contributes to the overall stressed appearance of heavily infested plants. Removing and binning damaged buds before the adults emerge reduces the next generation of weevils in the garden.
Powdery mildew can affect hollyhocks during dry spells, coating the leaf surface with a white floury deposit and causing the margins to pucker and curl. It tends to be secondary to rust and most visible on plants already weakened by rust infection or grown in crowded conditions with limited airflow. Leaf spot diseases, caused by various fungal pathogens, produce circular brown spots on the leaves and are favoured by wet summers and poor air circulation. Waterlogging causes yellowing and general collapse rather than classic curling, but persistently wet roots produce a plant that looks wilted and tired even when rainfall has been recent.
Prevention: the annual routine that keeps hollyhocks healthy
- Clear and dispose of all fallen hollyhock leaves, stems, and debris in autumn. Put them in the bin or burn them rather than composting: rust spores survive on dead material and reinfect the following year's plants.
- Start preventive copper or myclobutanil fungicide sprays in May, before any rust symptoms appear, and repeat every two to three weeks through summer. Apply to both leaf surfaces.
- Space hollyhocks generously and avoid crowding them in borders. Good airflow between plants slows rust spread and reduces powdery mildew.
- Grow hollyhocks at the base of a wall or fence in the traditional cottage garden position. The shelter reduces leaf wetness and gives plants a dry run-off behind them, which limits spore germination and spread.
- Water at the base of the plant rather than overhead. Wet foliage accelerates rust spread and provides conditions for powdery mildew and leaf spot to establish.
- Try varieties from the Halo series or consider Alcea rugosa if rust is severe every year in your garden. They are not immune but perform noticeably better than heritage singles and doubles in high-pressure situations.
Frequently asked questions
Why do hollyhock leaves curl upward?
Upward leaf curl on hollyhocks is the most recognisable symptom of hollyhock rust (Phragmidium malvacearum). Turn the leaf over and look for orange-brown powdery pustules on the underside; the upper surface will show corresponding small yellow-orange spots. Rust is almost universal in UK cottage gardens and spreads most rapidly in warm, humid conditions from June onward. Remove affected leaves, clear all fallen foliage at the end of the season, and use a copper or myclobutanil fungicide from May the following year.
Can aphids make hollyhock leaves curl?
Yes. The black bean aphid (Aphis fabae) and the hollyhock aphid (Aphis althaeae) both colonise hollyhocks, forming dense black or grey clusters on young shoots and stems. Their feeding causes the leaves to curl downward rather than upward, and the sticky honeydew they excrete attracts sooty mould. Inspect shoot tips and the undersides of new leaves from April onward. Rub colonies off by hand or use an insecticidal soap spray on heavier infestations.
Is hollyhock rust fatal?
Hollyhock rust rarely kills plants outright in a single season, but repeated heavy infection significantly weakens them, reduces flowering, and shortens their useful life as biennials. The lower leaves are typically the first to be defoliated, working upward through the plant as summer progresses. Preventive fungicide sprays starting in May, combined with scrupulous autumn clearance, can keep plants attractive and productive for longer. Choosing varieties from the Halo series, which shows better resistance than heritage cultivars, also helps in gardens where rust pressure is very high.
What is the best preventive spray for hollyhock rust in the UK?
In the UK, gardeners have two main options. Myclobutanil-based fungicides (available as Bayer Fungus Fighter and similar products) give good systemic protection and should be applied from May onward, repeated every two to three weeks through summer. Copper-based fungicides (such as Bordeaux mixture or copper oxychloride) are a traditional alternative and can be used on an organic basis. Neither product cures existing rust; both work preventively by protecting healthy tissue from new infections. Always coat both the upper and lower leaf surfaces, where the spores land.
Why are there tiny holes and distorted buds on my hollyhocks?
Tiny pitted holes in young expanding leaves with a slightly scorched or tatty look are typical of capsid bug (Lygus rugulipennis) feeding. Capsids inject toxic saliva into the growing tissue, which causes irregular holes and distortion to appear as the leaf expands. Hollyhock weevil (Rhopalapion longirostre) produces a different pattern: bored holes in flower buds and distorted buds that fail to open. Both are difficult to treat chemically as feeding happens at night, but removing weevil-damaged buds before the adults emerge helps reduce populations.