Aerial Survey Reveals Diseased Larch in the Tywi

Red Squirrel - Becca Vincent

Red Squirrel – Becca Vincent

NRW Aerial Surveys

NRW Aerial Surveys

Red Squirrel News...

This May, Natural Resources Wales (NRW) carried out aerial surveys to gauge tree health, primarily focusing on Phytophthora ramorum, (P. ramorum) a plant pathogen which is known to be affecting larch.   P. ramorum is a fungus-like pathogen which causes extensive damage and mortality to a wide range of trees and other plants.  Initial findings have identified 130 new suspected sites across Wales; 100 of the sites are located in the West-Mid Wales area, some blocks with 25% to 50% of trees that are showing symptoms of infection.  The photo above shows affected larch in nearby Brechfa Forest.  These findings represent a significant increase of infection in larch in the Tywi Forest.  Symptoms on larch include withering of shoots and foliage, visible as wilted shoot tips with blackened needles which shed prematurely and numerous resinous cankers on the branches and upper trunk.  An initial drive around some of the suspect sites in the northern Tywi has revealed symptoms that indicate infection with P ramorum such as foliage dieback. Samples were taken and have been sent to the laboratory for analysis.

Results of NRW Aerial Surveys

P. ramorum is spread by air; one of the major mechanisms of dispersal is rainwater splashing spores onto other susceptible plants, and into watercourses to be carried for greater distances.  The reason for this sudden increase in infection is unknown, but could be due to the combined effect of a very wet winter in 2015, with opportunity for sporulation and infection, followed by a very mild winter in 2016/17.  This weather pattern may have allowed infections to grow aggressively over winter with symptoms becoming apparent this spring.

No cure has been found and there are no effective chemical treatments available. So the objective of any control approach is to prevent or minimise any further spread of P. ramorum and the damage it causes. The best solution currently available is to kill the living plant tissue on which the organism depends for reproduction. In the case of infected larch, this means affected trees will be felled or otherwise killed as quickly as possible after detection of the disease and before the next spring or autumn period of sporulation begins on the needles.  NRW serve Statutory Plant Health Notices (SPHNs) on woodland owners requiring their infected trees to be felled.

Larch is quite significant for the forest industry, but is not a native species, so what's all the fuss about?  P. ramorum affects not only larch, but several other tree species in Britain.  Susceptible trees include beech, sweet chestnut and horse chestnut.  It has also been confirmed on a small number of Sitka spruce, a commercially crucial conifer species which is widely grown in the British Isles.  If P. ramorum were to infect Sitka spruce on a wide scale, this would be disastrous for the Forest industry.  P. ramorum is also a concern for the survival of red squirrels in mid Wales.  Larch is a key food species for red squirrels in mid Wales, the loss of which will certainly have a negative impact on our reds.  Sitka spruce represents over 75% of red squirrel habitat in mid Wales, if Sitka spruce in the Tywi forest becomes infected, the subsequent loss of habitat could be devastating for the red squirrel population.

Simple precautions such as cleaning footwear, tools, vehicles and clothing are strongly advised in outbreak areas to prevent further spread.