Using mathematics to predict and prevent tree diseases

22nd Apr 2013

Trees in the UK face an uncertain future from threats such as climate change, bringing more and more extreme weather, and the recent rise in exotic pests and diseases coming into the country.

The number of new diseases entering the UK has risen dramatically in the past decade. Current problems include, Phytophthora ramorum, a pathogen that is a significant problem on commercial Larch trees in the UK, and Acute Oak Decline, a disease that has been linked to a bacterial species that can kill oak trees.

Ash Dieback is the latest example that can cause extensive economic and environmental damage. This devastating disease, caused by a fungus called Chalara fraxinea, threatens ash trees and woodlands across the country. The disease has been a problem in Poland since the early 1990s and was first found in the UK in February 2012.

Rothamsted scientists are developing predictive mathematical models to examine how epidemics spread, which can be used to inform surveillance programs for invading diseases. These models investigate questions such as: what is the probability to find an invading epidemic before it gets to a high incidence in the environment? How do we design a surveillance program to detect and delimit as many new local outbreaks as possible? 

Effective surveillance is crucial in order to discover new diseases before they get out of control. However, finding the small handful of diseased trees that start an epidemic in the vast UK landscape can be like trying to find a needle in a haystack. Predictive models of epidemics can be used to hone surveillance programs and identify which areas in the UK are most at risk and thus should be prioritised to visit and look for diseases.

These issues were highlighted by Dr Stephen Parnell on Saturday 13th April, when Rothamsted Research hosted the 2013 Hertfordshire Tree Wardens Forum. The Tree Warden Scheme is a national initiative that aims to enable people to play an active role in conserving and enhancing their local trees and woodlands. Tree Wardens are volunteers appointed by parish councils or other community groups and are responsible for gathering information from their local trees, getting involved in local tree matters and encouraging local practical projects in trees and woodlands, which can help to combat such threats. There are 8000 members nationwide organised across 150 local networks in towns, cities and the countryside Tree Wardens. Dr Stephen Parnell’s talk at the Forum described the problems trees face from new diseases and what can be done to try and prevent them.

Volunteer groups such as the Tree Wardens, who have a good understanding of trees and woodland environments and the issues that plague them, have a strong potential role to play in finding and reporting new tree disease outbreaks. The more eyes and ears on the ground looking for disease symptoms the greater the chance of controlling current threats such as ash dieback and that the next invading disease on the horizon will be spotted and stopped as early as possible.

‘Citizen science’ is about volunteers getting involved in solving scientific challenges, such as those laid down by current tree disease threats. By helping to look for tree diseases volunteers can help to protect their local environments. The Forestry Commission website contains information and photographs of disease symptoms on a range of current threats that can help people to know what they are looking for.

Dr Stephen Parnell an epidemiologist at Rothamsted Research said “the UK has seen a recent rapid rise in the number of new tree diseases. Ash dieback is a good example of the impact these diseases can have. Volunteer groups such as the Tree Wardens are perfectly positioned to help the fight against these invaders by helping to quickly identify potential new outbreaks in their local communities and countryside.”

The scientists at Rothamsted have also recently been involved in a funding initiative from the Biotechnology and Biological Sciences Research Council (BBSRC) to apply their methods in response to ash dieback. Rothamsted scientists will work in collaboration with researchers at the University of Cambridge to develop models to identify the patterns, causes and effects of the disease and to improve surveillance and control strategies, with Rothamsted focusing on surveillance.

Agricultural crops face similarly grave challenges from invading pathogens and the researchers at Rothamsted are also applying their modelling approaches to improve surveillance for invading diseases of wheat and other agricultural commodities and the Rothamsted scientists will also be using their expertise in mathematical modelling to help achieve the goal of delivering the knowledge and new practices to increase crop productivity and quality and to develop environmentally sustainable solutions for food production and bioenergy.

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