Cupressus Foliage Browning and Dieback
Cypress canker and Phytophthora root rot are the most serious reasons cupressus foliage browns. This guide shows you how to identify each cause and keep Italian cypress and Monterey cypress in healthy, upright form.
1. Cypress canker (Seiridium)
Cypress canker, caused by Seiridium cardinale and related species, is the most serious disease of ornamental cupressus in the UK and Europe. The pathogen infects the tree through bark wounds, pruning cuts, insect damage, and natural bark cracks, causing progressively enlarging cankers that girdle branches and eventually the main stem. Cupressus macrocarpa (Monterey cypress) is among the most susceptible species. The disease is most active in warm, dry conditions and has become more prevalent as UK summers have warmed.
What to look for
Sections of foliage on individual branches turn reddish-brown and wilt suddenly, while adjacent branches remain green. This 'flagging' pattern, where dead reddish sections appear randomly distributed across the canopy, is characteristic of canker disease. Examining the bark at the base of the affected branch reveals a sunken, darkened, often resin-soaked elliptical canker where the pathogen has girdled the branch. The resinous exudate has a distinctively dark appearance and the bark beneath is dead. Multiple flagging events across the canopy, or a canker on the main trunk, indicates serious infection likely to be terminal.
What to do
Prune out affected branches promptly, cutting well below the last visible margin of the canker into healthy wood. Make clean cuts in dry weather and sterilise tools between cuts. Bin all removed material. For cankers on the main trunk, surgical removal of the infected bark tissue is sometimes attempted but is rarely successful once the canker has girdled more than a third of the trunk circumference. Reduce susceptibility by avoiding unnecessary pruning cuts and keeping pruning to dry weather periods; pruning wounds in wet conditions are primary infection entry points. There is no effective fungicide treatment once the canker is established.
2. Phytophthora root rot
Phytophthora root rot, caused by Phytophthora cinnamomi and related species, causes progressive root death in cupressus, leading to foliage yellowing and browning that begins at the base of the plant and spreads upward. Cupressus is significantly more susceptible to Phytophthora than, for example, Thuja plicata, and the disease is most active in warm, wet conditions. Plants in poorly draining soil or in low-lying positions accumulating water are most at risk.
What to look for
Foliage transitions from normal green to grey-green, then yellow, then reddish-brown, in a progressive pattern beginning at the base of the plant and spreading upward. The browning does not respond to watering and the plant looks poorly despite moist or wet soil conditions. Unlike cypress canker, which affects individual branches randomly distributed through the canopy, Phytophthora browning progresses upward in a consistent basal-to-tip pattern. Scraping the bark at the base of the stem reveals reddish-brown discolouration rather than healthy green or cream. The roots, if examined, are dark and rotten.
What to do
There is no effective chemical cure. Remove affected plants and replace as much surrounding soil as possible before replanting. Improve drainage in the affected area before introducing new plants. Do not replant susceptible cupressus species in soil where Phytophthora has been present. Thuja plicata (western red cedar) is a significantly more Phytophthora-resistant alternative for hedging that provides similar dense, formal screening. Prevent spread by not moving soil or plant material from affected areas to other parts of the garden.
3. Cypress aphid
The cypress aphid (Cinara cupressi) is a large, dark grey to brown aphid that colonises the bark and foliage of cupressus, forming dense colonies particularly on young growth. It feeds by piercing the bark and scale-like foliage, causing yellowing and browning that can affect whole sections of the plant rapidly. Infestations are most damaging in late summer and autumn, and the browning caused by cypress aphid is sometimes mistaken for cypress canker or Phytophthora.
What to look for
Patches of foliage turn yellowish-brown over a short period, beginning in areas where aphid colonies are concentrated. Close inspection reveals large, slow-moving dark aphids, each three to four millimetres long, clustered on the bark and scale foliage throughout the affected area. A sticky honeydew coating on the foliage below the colonies leads to black sooty mould development. Unlike canker, which kills foliage above a discrete bark lesion, aphid browning affects foliage at the colony site rather than above it, and colonies are visible by direct inspection rather than only detectable by bark scraping.
What to do
For small or young plants, spray the affected areas thoroughly with horticultural soap solution, targeting the colonies directly. The large size of these aphids makes them relatively easy to knock off with a strong jet of water from a hose. On large established hedges, natural predators including ladybirds and parasitic wasps provide significant control without intervention in most seasons. Avoid broad-spectrum insecticides that eliminate beneficial predator insects. A mid-autumn inspection, when populations are at their autumn peak, helps identify and treat colonies before they overwinter and rebuild the following year.
4. Cold and frost damage
Cupressus sempervirens (Italian cypress) is the most cold-sensitive of the commonly grown cypress species in the UK and can suffer severe foliage browning or dieback in hard winters. It performs best in the warmest, most sheltered positions in southern and south-western England and is a significant risk in colder, more exposed gardens or in the midlands and north of England. Cupressus macrocarpa is somewhat hardier but can also suffer in severe winters, particularly in young or weakened specimens.
What to look for
Foliage turns reddish-brown across large areas or throughout the whole plant following a period of prolonged hard frost. Unlike cypress canker, which affects individual branches in a random flagging pattern, cold damage affects the whole plant or at least the most exposed face. The damage appears suddenly after cold weather rather than progressing over weeks. In mild cold damage, the tree may retain most of its structure with only superficial browning; in severe frost the whole plant browns and dies. Young trees, trees in exposed positions, and newly planted specimens are the most vulnerable.
What to do
Do not prune cold-damaged cupressus until late spring, when new growth confirms which material is still alive. Then prune to the first point of live growth. For Italian cypress in borderline positions, wrapping with horticultural fleece or hessian during forecast severe frost periods provides meaningful protection in the first few winters. Choose a sheltered, south or south-west-facing position in full sun, preferably against a wall or building that provides thermal mass. In genuinely cold gardens or in the north and midlands, choosing a hardier alternative such as x Cuprocyparis leylandii is the practical solution.
5. Drought stress
Young cupressus in their first two to three years after planting are susceptible to drought stress, despite the fact that established Italian and Monterey cypress are among the more drought-tolerant conifers available. The establishment period requires consistent moisture support, particularly on free-draining soils in hot summers, before the root system extends beyond the original planting hole into the wider soil moisture reservoir.
What to look for
Scale foliage on the shoot tips turns pale tan or bleached brown, with the colour change most pronounced on the most exposed outer growth in the hottest part of the summer. Unlike cypress canker, drought browning affects shoot tips uniformly rather than producing the discrete flagging pattern of branch death above a specific bark lesion. The soil beneath the plant is very dry at depth. The problem is most common in the first summer after planting, especially if the plant was pot-grown with a compact root ball that has not yet extended into the surrounding soil.
What to do
Water newly planted cupressus deeply at least once a week during any dry spell in their first two growing seasons. Apply a mulch of bark chip or gravel around the base to conserve moisture. Once established, particularly Italian cypress, is genuinely drought-tolerant and rarely requires supplementary irrigation; its reputation as a drought-tolerant Mediterranean tree is well deserved in mature specimens. The first two summers after planting are the critical window where consistent moisture support determines whether the tree establishes vigorously or struggles for years.
Frequently asked questions
What is cypress canker?
Cypress canker is caused by the fungal pathogen Seiridium cardinale (formerly Coryneum cardinale), which infects cupressus through bark wounds, pruning cuts, and natural openings. The pathogen causes elliptical, sunken, resin-soaked cankers on branches and the trunk that disrupt water movement, causing the foliage above the canker to wilt and brown. The foliage on affected branches turns reddish-brown in a pattern sometimes described as 'flagging'. Cypress canker is widespread throughout the UK and has been responsible for the death of large numbers of ornamental cupressus trees, particularly Cupressus macrocarpa and Italian cypress.
Is Cupressus sempervirens (Italian cypress) hardy in the UK?
Cupressus sempervirens (Italian cypress) is borderline hardy in the UK and performs best in the warmest, most sheltered positions in southern and south-western England. In cold winters, particularly with prolonged frost below minus 10 Celsius, the foliage can brown severely and the tree may suffer significant dieback or death. Young trees in their first few years are the most vulnerable. In colder parts of the UK it is a risky choice; the cultivar 'Totem' is considered slightly hardier than the straight species. In a warm, sheltered, south-facing position in southern England, established trees survive most UK winters without significant damage.
Can cupressus recover from browning?
Whether cupressus recovers from browning depends entirely on the cause. Cold and wind damage on otherwise healthy trees typically recovers as new growth emerges in spring, especially in sheltered positions. Drought tip browning on young trees resolves with improved watering. However, cypress canker does not recover; the affected branch will die completely once the canker has girdled it, and the foliage cannot regenerate. Similarly, Phytophthora root rot is usually irreversible. Cupressus does not regenerate foliage on old bare wood, so recovery relies on existing live growing points producing new growth.
Why is my Monterey cypress going brown?
Cupressus macrocarpa (Monterey cypress) is highly susceptible to cypress canker (Seiridium cardinale), which is the most common serious cause of browning and dieback in this species in UK gardens. The canker produces sections of wilted, reddish-brown foliage on individual branches, with resinous lesions visible on the bark at the base of the affected section. Cypress aphid (Cinara cupressi) also causes foliage browning and can be severe. Cold damage in hard winters causes more general foliage discolouration across the whole tree, while drought on newly planted specimens causes tip browning.
Is there a disease-resistant alternative to Cupressus macrocarpa hedging?
Yes. The hybrid x Cuprocyparis leylandii (Leyland cypress), which is a cross between Cupressus macrocarpa and Chamaecyparis nootkatensis, is significantly more resistant to Seiridium canker than the straight Cupressus macrocarpa parent. However, Leyland cypress has its own problems including susceptibility to Seiridium canker in some conditions and to Phytophthora. For a genuinely disease-resistant alternative, Thuja plicata (western red cedar) offers excellent hedging characteristics and very high resistance to the major diseases affecting Cupressus.
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