A key objective of the LTOA is to 'Improve the health, increase the extent and guarantee the resilience of London’s tree canopy'
Despite the many positive changes, and increases in awareness, understanding and practice in recent years in relation to our natural heritage and care for our environment, we are beset everyday by greater threats to the ecosystem we inhabit.
The LTOA is responsible for much of London’s tree population, a fundamental part of the environment, and the keystone species that support humans and wildlife and interconnect the entire city’s natural and physical processes, its water, soil and the very air we breathe.
We are increasingly informed about the importance of our tree canopy for air conditioning, and managing water, soil and drainage systems, the effectiveness of which is essential to the quality of urban living. The increasing risks of new pests and diseases to London’s trees, if unchecked, threaten the canopy and skyline as we know it today.
The prospect of such declines and losses places a clear responsibility on government, municipal managers, LTOA members and the public to invest in protecting our trees if we are to secure and enhance their contribution and continuity for the benefit of city life.
This position statement reflects current concern about a number of significant pest and diseases threatening the health of London’s trees, including:
- Acute Oak decline (AOC)
- Canker Stain of Plane (CSP) Ceratocystis platani
- Chalara Ash Dieback (CAD) Hymenoscyphus fraxineus
- Horse Chestnut Leaf Miner (HCLM) Cameraria ohridella
- Massaria Disease of Plane (MDP) Splanchnonema platani
- Oak Processionary Moth (OPM) Thaumetopoea processionea
Pests and Pathogens of London's Trees
The LTOA biosecurity working party has drawn up a matrix showing the pest and pathogens of London's trees. Listing pests / pathogens and species affected, diagnosis, prognosis, management and information links. Click on this link for the matrix.
Xylella Fastidiosa - Bacterial leaf scorch
Bacterial leaf scorch disease is caused by the bacterium Xylella fastidiosawhich affects a wide range of amenity tree species. It also affects economic hosts such as grapevine (as Pierce’s disease of grape) and citrus species (as citrus variegation chlorosis). In Europe, olive and almonds are the main crops affected. The pathogen has four known subspecies:fastidiosa, ssp. pauca, ssp. multiplex, and ssp. sandyi,each havingdifferent host ranges. The multiplexstrain is considered to pose the greatest plant health risk to the UK andcan probably infect the widest range of host plants, including Platanus(plane spp.), Quercus(oak spp.), Acer (maple spp.), Ulmus (elm spp.) and Ginkgo biloba(maidenhair tree). Afull list of confirmed hosts for EU outbreaks can be found on the EU CommissionXylellahost list.
Symptoms of X. fastidiosamanifest themselves differently in different host species, but the visible symptoms on plane, maple, oak and elm include leaf scorch, sometimes also with dieback of twigs and branches. The characteristic leaf symptoms which are visible in summer include browning at the leaf margins (but not along the main veins), and there is often a yellow edge (“halo”) to the browned areas. Scorched leaves tend to drop from the distal and not the basal end of the petiole, leaving bare petioles attached.Older leaves will have a "scorched" curled appearance while younger leaves at branch tips can appear healthy.Other symptoms include defoliation, shoot dwarfing, dehydrated fruits, irregular patches of brown and green tissue and reduced growth. Heavily infected plants may die within one or two years. A number of other disorders can produce symptoms similar to those caused by X. fastidiosa, including the fungus Guignardia aesculion Aesculus hippocastanum(horse chestnut),Dutch elm disease, anthracnose (Apiognomonia veneta)on plane trees and powdery mildew (Erysiphe platani) on young plane leaves.
In mid-October 2013 X. fastidiosawas detected in southern Italy. There are also known outbreaks of X. fastidiosain France (Corsica and mainland France), Germany and Spain (islands of Mallorca, Menorca and Ibiza and mainland Spain).
The bacteria are transmitted by insects which feed on plants' xylem fluid. There are several species of insects in the UK which could vector (spread) X. fastidiosa, including the common froghopper (Philaenus spumarius). Long-distance spread can occur by the movement of infected plants for planting.
The LTOA have been actively looking for symptoms of X. fastidiosaas part of the PZS Ceratocystis platanisurveys. As of February 2018 X. fastidiosahas not been positively identified in the UK.
Xylellais subject to EU emergency measures. The control strategy primarily aims to keep the bacterium out of the UK and other currently unaffected Member States if possible, although its large host range and complexity of symptoms make X. fastidiosaextremely difficult to detect. In the UK, pending landings of Xylellahost species, such as plane, elm and oak plants, must be pre-notified to the plant health authorities to enable inspection. X. fastidiosa is a quarantine organism so there is an obligation to report any suspect trees to plant health authorities.
Here’s a link to the Plant Health Portal high risk host list https://planthealthportal.