UK landscapes could be at risk from another major tree epidemic unless awareness is raised, say researchers

7th Feb 2011

We must be more vigilant to disease threats or risk serious consequences for our familiar landscapes and gardens, according to researchers carrying out investigations as part of the Rural Economy and Land Use (RELU) Programme, which is funded by BBSRC, the Economic and Social Research Council and Natural Environment Research Council.

Social and natural scientists have been looking back at the outbreak of Dutch elm disease that ravaged the UK in the 1970s and considering the implications for our natural heritage today. One tree disease of particular concern is Sudden Oak Death, caused by Phytophthora ramorum, which has been on the rise in the UK in recent years. This fungus-like pathogen, along with its relative Phyotophthora kernoviae, has the potential to kill large numbers of trees across a wide range of species, with serious consequences for heritage gardens, rural landscapes and the horticultural trade.

The RELU-funded team have identified fundamental lessons that need to be learnt, and make some important recommendations for key groups involved in biosecurity.

In particular, they suggest that government agencies and third sector environmental groups could give more attention to the threat that invasive diseases pose to biodiversity, and use their influence to raise the awareness of both policymakers and the public. The latter would help to ensure that gardeners and tourists visiting gardens become more conscious of the dangers of cross-infection and the precautions that they should be taking.

Dr Clive Potter from Imperial College London who led the project said, "Valuation surveys from our research suggest a lack of public awareness and this translated into an unwillingness to pay for control measures. Public awareness needs to be raised, not only in order to establish a stronger sense of personal responsibility for preventing the spread of plant diseases, but also to elicit more support and a greater willingness to pay for any more restrictive measures and policies that may be necessary in the future if we are to avoid another epidemic like Dutch elm disease."

Diseases tend to come into the UK via imported plants and the researchers say we need to acknowledge the difficult trade-offs that will need to be made between freer trade and effective biosecurity.

"European legislators have a part to play, as well as the UK Government and a wide range of stakeholders, in tackling this growing problem," says Potter.

"There is a need for a more critical and interdisciplinary analysis of the underlying causes of the growing threat to biosecurity, and of conflicts between those advocating further market liberalisation in the context of the Single European Market and those arguing for restrictions on trade in the interests of biosecurity."

Modelling the risk of disease spread for optimal control

In related research funded by BBSRC, scientists at the University of Cambridge have devised a suite of models to predict how the disease is likely to spread. The models are used to identify those regions at most risk to disease and to compare different scenarios to manage the spread of the epidemic.

Culling of susceptible vegetation around infected trees is a widely used measure for the control of several pathogens but culling first requires detection of often cryptically-infected hosts. Here the models help by identifying how best to allocate resources for detection and for sudden oak death control whilst preserving biodiversity when the budget is limited.

Professor Chris Gilligan, Head of the Epidemiology and Modelling group in the Department of Plant Sciences, explains, "Contrary to simple expectations our results show that committing resource for intermediate levels of detection and using the remaining resource for control is optimal. Low levels of detection, characteristic of low effort expended on searching and detection of diseased trees, and high detection levels, exemplified by the deployment of large amounts of resources to identify diseased trees, fail to bring the epidemic under control.

"Importantly, we show that a slight change in the balance between the resources allocated to detection and those allocated to control may lead to drastic inefficiencies in control strategies. These results also hold when quarantine is introduced to reduce the ingress of infected material into the region of interest."

Gilligan believes that this methodology can be applied to a wide range of host-pathogen systems in which budgets have to be allocated to detection and control and that intermediate levels of detection are likely to prove optimal for many of them.

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