On two sunny spring days at Kew Gardens a conference with a rather sober topic took place: tree health early warning systems. In other words, how can we as a global community spot foreign tree pests and diseases of concern before they take hold in our respective countries?

The conference was hosted by Observatree and the International Plant Sentinel Network, which monitors trees and plants around the world for their response to pests and diseases. It attracted some key professionals in tree health from the UK and across the world – 150 delegates in total from 20 countries including the USA, Russia and New Zealand.


There is a risk from a steady stream of accidental introductions of new pests and diseases, especially via imports of mature trees and shrubs from Asian trade routes. Many of the organisms of concern to us live in harmony with their host plants or trees in their country of origin and cause no threat there: it is when they arrive in a new location with plants and trees with no resistance and no natural predators that a problem can arise.

The potential risk of the Emerald Ash Borer beetle arriving in the UK is the one that concerned me the most. Prof Deborah McCullough from Michigan explained the devastation it has wreaked on American ash species in 25 states with economic costs of dead trees to date of $850 million.

More worrying from a UK perspective is the fact it has shown a liking for European ash and is currently moving west from Moscow. Two factors are of particular concern; the first is that trees can appear healthy for several years despite having infestations and secondly that it is almost impossible to successfully lure and trap the adult beetles. So by the time an outbreak is discovered it could have spread very widely. And of course in the UK trees already weakened by Chalara dieback of ash would have little chance against this pest.

I was also interested in the concept of the ‘unknown unknowns’ – sometimes pests are found which are new to science and therefore not previously on anyone’s radar. As one delegate elegantly put it “not so much looking for a needle in a haystack, but not even being sure if it is a needle you are looking for”.


International collaborations taking place were positive news. The International Plant Sentinel Network aims to use collaborations of botanic gardens and arboreta across the world. Their role is to identify potential pests and diseases of future concern before they cross borders by looking at how plants, such as English Oak in places like botanic gardens in China, respond to local pests and diseases. This would give an idea about what may happen if the particular pest or disease were to arrive in the UK and whether it would pose a risk or not.

Some of the new technologies on offer seemed promising. One company has attempted to use ‘hyperspectral sensing’ to identify different species of trees from the air and even pick out sick ash trees. But it sounds like there is a long way to go before these techniques will become viable.

On a positive note for the next generation, plant health now features on the GCSE curriculum for the first time. Thousands of schools have been engaged in the issue via OPAL (the Open Air Laboratory citizen science scheme) and work is being done by DEFRA to promote plant health as a valued and attractive career.

It was inspiring to hear how the public can become really engaged by an issue. For example, in the UK, through initiatives like volunteering for Observatree. Also, citizen scientists can provide capacity to cost-effectively monitor bigger areas over longer timescales than would be possible just using paid scientists alone.

Success stories

There were some good news stories. For example eradication of the Great White butterfly in New Zealand that was threatening their rare wild cabbage populations, plus the story of the rapid action against Oriental Chestnut Gall wasp in the UK, which I’m delighted to say Observatree volunteers played a pivotal role in. An emerging successful trunk injection treatment against emerald ash borer sounded promising for certain situations: it is working well on urban ash trees in US cities and buying some time to allow more diverse species to be planted as future replacements.

I found this an inspiring conference, particularly around the international collaboration that is taking place on an issue that affects us all. But I left with a strong sense that all of us have a responsibility to help whoever we are, whether through better personal biosecurityreporting pests and disease of concern or taking part in different citizen science projects on offer.