Plant Health Questions & Answers

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Horse Chestnut Bleeding Canker

This is caused by a bacterium, Pseudomonas syringae, pathovar aesculi. From a tree survey conducted across the UK in 2007, it was discovered that half of all trees surveyed showed some symptoms. This disease was first seen in the UK in 1970 and is thought to have arrived from India. Trees of all ages can be affected. Some infections can last for years with little impact on the crown but in other cases the spread can be rapid causing crown thinning, die back and sometimes death of part or of the whole tree. Symptoms noted are cracks in the bark and oozing of a reddish brown sticky liquid. These dry in the winter to leave a rusty brown or black deposit. Under the bark the wood is found to be discoloured with brown or purple discolouration as opposed to the usual white/pinkish colour. In older plants dead bark may fall away to expose the wood beneath.

All plants now sold in the UK must be produced in the UK. If this bleeding canker is observed it should be reported to plant health authorities via Tree Alert at

(this information was found on the Woodland Trust website

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Horse Chestnut leaf blotch fungus

This is caused by the fungus Phyllostica paviae. Irregular brown blotches of dead tissue are seen on the leaves. Sometimes these have a yellow edge and sometimes the leaf shrivels totally. This is more prevalent in the south and west of the U.K. and was introduced to this country from N. America in the twentieth century.

Horse chestnut leaves are also sometimes seen to gradually turn brown and shrivel all round the edges, looking like severe water stress. This is not leaf blotch and the cause of this condition is not yet known. (this information was found on the RHS website

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Horse Chestnut leaf mining moth.

This was first found in the UK in 2002 and the moth concerned is Cameraria ohridella. White or brown batches are seen on the foliage from June to September. Caterpillars or circular pupal cocoons can be seen in the mined area of the leaf if it is held to the light. By September the tree may look as if it is dying but it will survive. Leaves may be dropped early and conkers may be smaller. (this information was found on the RHS website

Marion Kinns,

“There are three potential problems which could affect Leyland Cypress trees – a blight, a canker and root rot. There is also a pest, an aphid.”

Marion Kinns,

Cypress needle blight

This is caused by another fungus, Passalora sequoia. Symptoms are needles browning and dropping, usually beginning on the lower branches. Spores are spread by rain, winds and tools. To avoid this disease, trees for hedging should be placed far enough apart to allow sun and air to pass through the branches. Infected branches should be pruned out and the loppers used should be sterilised. Do not chip or compost infected branches.

Marion Kinns,

Canker in Cyprus trees

This is another fungal disease and is caused by either Seiridium unicorne or by Botryosphaeria . In the former, the cankers rarely girdle the stem and in the latter they can girdle the stem. The cankers are dry lesions and are often sunken. Surrounding bark can show dark brown or purple discolouration and water flow can be restricted by these cankers. Branches can be seen to die back and there can be oozing of sap. It is found that canker tends to occur only on stressed plants. Fungicides are not effective. Recommendations are to plant trees a minimum of 12-15ft apart and avoid over fertilising. Infected branches should be pruned out, sterilising the pruners. A programme of regular irrigations should be followed and the trees should be mulched to the drip line.

Marion Kinns,

Root rot

Species of Phytophthera fungus are responsible for this condition. Roots die off and foliage goes yellowish, purple or tan. The whole of the tree is affected. There is no chemical treatment. It is often caused by planting where the drainage is poor and young plants are most often affected.

(information for the above three diseases was found at and the RHS website

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Cypress aphid (Cinara cupressiora)

Damage develops in late spring and summer and is most often found initially at the base of a hedge. The pest is a large greyish greenfly. Brown patches often develop after the aphids have gone. It is, however, possible to see cast aphid skins and sooty mould which grows on the honeydew excreted by the aphids. Damaged hedges can recover but this can be a slow process. The RHS suggests the use of biological controls to avoid killing beneficial insects. Information from RHS website

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