Salix Leaves Curling

Willow rust

Willow rust (Melampsora species, primarily Melampsora epitea and related species) is one of the most widespread fungal diseases on salix in the UK, producing bright orange or yellow powdery pustules on the undersides of the long, narrow leaves from midsummer and causing the surrounding tissue to distort, pucker, and curl as the spore structures develop. The disease is visible first as pale yellow flecks on the upper leaf surface, corresponding to orange urediniospore pustules on the lower surface that burst through the epidermis as they mature. In heavy infections, the undersides of willow leaves can be almost entirely covered in orange rust pustules, and the combined weight and distortion of the fungal structures causes the leaves to curl downward and backward around the affected areas. Willow rust is particularly common in wet growing seasons and on willows planted in positions with poor air circulation, where the leaf surfaces remain wet for extended periods after rain and allow rapid spore germination and penetration. The rust weakens the leaves and causes premature drop in severe infections, potentially reducing the vigour of the affected willow in the season following a heavy attack by reducing the photosynthetic capacity available for storage before leaf fall.

Collect and destroy fallen infected willow leaves in autumn to reduce the spore reservoir for the following season. Improve air circulation around willows in enclosed or sheltered positions by appropriate pruning to reduce the microclimate that favours rust development. On ornamental willows where rust has been severe in previous seasons, apply a copper-based fungicide from bud burst in spring at two to three week intervals to reduce the initial infection load; this preventive approach is more effective than attempting to treat established infections once the pustules are visible. Choosing willow species and cultivars with lower rust susceptibility for new plantings reduces the management burden; some species, including Salix alba (white willow) and its ornamental cultivars such as Salix alba Tristis, are more susceptible than others. Established willows tolerate even moderate rust infections without lasting structural damage, and in most garden situations rust is a cosmetic concern rather than a serious threat.

Willow anthracnose

Willow anthracnose (Drepanopeziza sphaerioides) is a fungal disease that causes dark brown or black spots and blotches on the leaves of salix in spring and early summer, with the affected leaf tissue distorting, puckering, and curling around the dead zones as the lesions enlarge and coalesce. The disease enters through the young, expanding leaves in spring during wet weather, and early infections cause the shoot tips to blacken and curl over in a symptom that superficially resembles fireblight, though willow anthracnose does not cause the characteristic shepherd's crook wilting associated with the bacterial disease. On severely infected leaves, the dark lesions expand and merge to cover large areas of the leaf surface, causing the whole leaf to distort, curl, and drop prematurely. Willow anthracnose is most severe in wet springs when prolonged leaf wetness provides ideal conditions for spore germination and infection, and on willows in sheltered positions where air circulation is limited and leaves dry slowly after rain. Pollarded willows that produce large quantities of soft, rapidly expanding new growth after pollarding are particularly susceptible to severe anthracnose outbreaks in wet springs.

Collect and destroy infected leaves in autumn to reduce the overwintering spore reservoir on fallen leaf debris. Where willow anthracnose has been severe in previous seasons, apply a copper-based fungicide from bud burst as the leaves emerge in spring, before the wet conditions that favour infection begin. On pollarded willows, timing the pollarding to autumn or early winter rather than late spring reduces the coincidence of the large flush of soft new growth with the peak spring infection period. Improving air circulation by appropriate management reduces the severity of infection in enclosed positions. Established willows tolerate moderate anthracnose without lasting impact on long-term health, though repeated severe infections over successive wet seasons can reduce vigour. Salix caprea and its cultivars including the weeping Kilmarnock willow show susceptibility to anthracnose and benefit from preventive management in wet spring conditions.

Aphids

Several aphid species colonise salix in UK gardens, and willow aphid (Pterocomma salicis), a large, dark brown to almost black aphid, is one of the most conspicuous, forming dense colonies on the young bark of willow shoots and small branches where it feeds on the phloem and causes the adjacent leaves to curl and distort. Other aphid species colonise the undersides of willow leaves directly, including the black bean aphid (Aphis fabae), which uses willow and spindle as its primary winter hosts before migrating to beans, nasturtiums, and other summer hosts in late spring. The migration of aphids off willow in spring is one of the mechanisms by which these pest species spread through gardens. On ornamental willows, including the popular Salix integra Hakuro-nishiki with its variegated pink and white spring foliage, aphid pressure on the new growth in spring can be severe, with the soft, colourful new leaves particularly attractive to colonisation. Honeydew from large willow aphid colonies accumulates on the leaves below and supports sooty mould development.

Natural predators including ladybirds, hoverfly larvae, lacewing larvae, and parasitic wasps are particularly effective at controlling aphids on willow, which is a structurally accessible plant that provides good habitat for beneficial insects. In most garden situations no intervention is needed, as predator populations build rapidly in response to aphid abundance. A strong jet of water directed at the affected shoots dislodges colonies effectively. Fatty acid spray provides contact control where aphids are causing visible distortion on young or ornamental willows. The black bean aphid's migration off willow in late spring means that willow aphid pressure on the tree itself is largely a spring phenomenon, resolving naturally by early summer as the winged forms fly off to their summer hosts.

Willow scab

Willow scab (Pollaccia elegans) is a fungal disease that causes dark olive-brown or black lesions on the young shoots and leaves of salix in spring, producing a distinctive scorched appearance on the new growth that emerges from the infected shoot tips in wet springs. The disease infects the expanding young leaves and the soft growing shoots before the tissue has hardened, causing the affected leaves to develop dark, greasy-looking lesions that kill the leaf tissue and cause the emerging leaves to curl, blacken, and die. Infected shoot tips curl over in a hook, superficially resembling fireblight, and the overall appearance of a heavily infected willow in a wet spring can be of severe scorching of all the new growth. Willow scab often occurs together with willow anthracnose in wet springs, and the two diseases compound each other's effects to produce a more severe combined impact than either alone. After the initial spring infection, the hardened summer growth is less susceptible, and the tree typically recovers and produces healthy growth through summer after the wet spring period passes.

Apply a copper-based fungicide from bud burst in spring on willows where scab has been severe in previous wet seasons, repeating at two-week intervals during wet spring weather. Remove and destroy infected shoot tips before the fungus sporulates to reduce the spread to adjacent growth. Improving air circulation around the tree reduces the prolonged leaf wetness that enables scab spore germination. On large established willows, treatment is generally impractical and the tree should be allowed to recover naturally once the spring infection period passes. For ornamental willows in prominent positions where the spring scorch is aesthetically unacceptable, removing and composting the worst affected shoots after the disease has run its course in spring promotes a new flush of clean summer growth. Choosing willow species and cultivars with lower susceptibility reduces the annual management burden in gardens where scab is a recurring problem.

Watermark disease

Watermark disease (Brenneria salicis, formerly Erwinia salicis) is a serious bacterial disease affecting weeping willow (Salix babylonica, Salix x sepulcralis Chrysocoma) and cricket bat willow (Salix alba var. caerulea) in the UK, causing the leaves on affected branches to wilt, curl, and turn red-brown before the branch dies back. The disease enters through wounds and spreads through the vascular system of the tree, blocking water transport and killing the infected branches. The characteristic watermark staining visible when infected wood is cut -- a reddish-brown discolouration in the outer rings of sapwood -- gives the disease its common name. Watermark disease can cause the progressive dieback of major branches over several seasons, and in severe infections the entire crown can be affected. The disease is particularly serious for cricket bat willow grown commercially, but is also a significant concern for the large, mature weeping willows that are valued landscape features in many UK gardens and public parks.

Remove all watermark disease-affected branches by cutting well into apparently healthy wood, sterilising cutting tools between every cut with a ten percent bleach solution or surgical spirit. Dispose of infected wood safely and do not compost it. There is no cure for watermark disease once established in a willow, and management is focused on removing infected branches to slow the spread through the tree's vascular system. Established willows that have a vigorous root system sometimes slow the progress of the disease through compartmentalisation, and the vigorous growth of willow species generally means that lost branches are replaced relatively quickly from new growth. For severely infected trees or trees where the disease is spreading rapidly despite branch removal, removal of the whole tree and careful clearance of the root system is the most appropriate response. Replanting with a species other than weeping willow or cricket bat willow on the same site avoids the risk of reinfection from soil-borne bacteria.

Frequently asked questions

Why are my willow leaves curling?

Willow rust (Melampsora species) causes orange or yellow pustules on the undersides of salix leaves and distorts the leaf blade as the fungal structures develop, causing the affected tissue to pucker and curl. Willow anthracnose (Drepanopeziza sphaerioides) causes dark brown spots and blotches on the leaves that coalesce in wet seasons to cause widespread discolouration, leaf distortion, and premature drop. Willow aphid (Pterocomma salicis and related species) colonises the shoots and leaves in spring and summer, causing the youngest growth to curl around the feeding colonies.

What is willow rust?

Willow rust (Melampsora species) is a fungal disease that produces bright orange or yellow powdery pustules on the undersides of salix leaves from midsummer, with corresponding pale yellow or orange spots on the upper surface. The rust is extremely common on salix throughout the UK and affects a wide range of willow species and cultivars. The leaf tissue around each pustule puckers and distorts slightly as the spore structures develop, and heavily infected leaves may show overall curling and premature drop. Willow rust has a two-host or multi-host life cycle involving different plant species, and the severity varies between willow species; some ornamental willows are considerably more susceptible than others.

Does salix get aphids?

Yes, several aphid species colonise salix in UK gardens, including willow aphid (Pterocomma salicis), which forms dense colonies on the bark of young shoots and branches and causes the adjacent leaves to curl and distort, and various smaller species that feed on the undersides of the leaves and cause the youngest growth to curl around the feeding colonies in spring. Willow is an important host for many aphid species, including the black bean aphid (Aphis fabae), which uses willow as a primary overwintering host before migrating to beans and other summer hosts in spring. Natural predators including ladybirds, hoverfly larvae, and parasitic wasps provide effective biological control of most willow aphid species.

Why are my weeping willow leaves turning brown?

Weeping willow (Salix babylonica, Salix x sepulcralis Chrysocoma) leaves turning brown most commonly indicate willow scab (Pollaccia elegans), which causes dark, olive-brown lesions on the young shoots and leaves in spring and early summer, particularly in wet seasons. Willow anthracnose produces similar dark spotting and browning that coalesces in severe infections. Watermark disease (Brenneria salicis) causes the leaves to wilt and brown in the characteristic shepherd's crook formation on weeping willow and cricket bat willow, with dark brown staining visible in the wood of infected branches. Drought stress in very dry conditions can cause browning of willow leaves, though established willows with access to moist soil are among the most drought-resistant of UK trees.