How Surrey trees are being affected by a new disease

PUBLISHED: 16:24 19 January 2015 | UPDATED: 16:07 27 January 2015

Archant

We talk to Hannah Pope from South East Tree Care Solutions, Surrey’s long-standing family run team of Tree Surgeons, about the new disease affecting a number of conifers in our county.

So what is Phytophthora lateralis?

Phytophthora lateralis is a relatively new disease found to be affecting Lawson cypress and a number of other conifers. It is a pathogen which generally attacks and kills the roots of its host trees, although aerial infections of branches and foliage also occur.

How quickly can it spread?

The disease spreads by tree roots coming into contact with P. lateralisspores present in the soil or water. Planting infected plants, or using soil which is harbouring spores, are key pathways for introducing the disease on to new sites. Once present in an area, spores from infected trees can also be spread in water run-off, or transferred on footwear.

We do not know how P. lateralis got into the UK, but the most likely route is that it entered on imported, containerised plants. We have not yet been able to confirm the pathways by which the pathogen got to these specific sites, although the fact that different genetic lineages of the pathogen are present at geographically close sites (i.e. Balloch and Greenock) suggests that separate, independent introductions of the pathogen have occurred.

What are the symptoms our Surrey residents should look out for?

The foliage of infected Lawson cypress trees initially turns a pale green, then a reddish-brown as the tree dies. As the pathogen extends from the roots and root collar up the trunks of affected trees, tongues of darker killed phloem (observable by removing the outer bark) become visible, contrasting with paler healthy tissue. The entire trunk can become girdled, leading to the tree’s death. Disease symptoms caused by P. lateralis can be confused with other infections such as those caused by Phytophthora cambivora or Armillaria spp, which are endemic to the UK.

What should they do if they suspect one of their conifers has fallen victim to the disease?

Infected trees should be felled and destroyed, either by burning, or chipping and deep burial - provided that no other Lawson cypress trees are in the vicinity.

How is it treated?

P. lateralis is a virulent pathogen which usually kills the trees it infects, primarily Lawson cypress. Few trees recover from an attack.

Lawson cypress is found throughout the UK, and we believe P. lateralisis capable of surviving in all parts of the UK. We estimate there are fewer than 2200 hectares of Lawson cypress growing in woodland in the UK. However, Lawson cypress and its many colourful cultivated varieties are popular for amenity planting in parks and gardens, and are among the most important conifers in the UK ornamental plant trade. This means it could represent a threat to the ornamental plant industry if it became established here.

P. lateralis also affects other cypress species and Pacific yew, a close relative of Britain’s native common yew (Taxus baccata). Its recent confirmation in western red cedar in the UK means it could prove a more significant risk to the forest industries, with about 1000 hectares growing in public forests.

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www.treecaresolutions.co.uk

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