The most recent in a long line of diseases threatening our native British woodland has recently been discovered in the south-east of the country. Originating from Asia this latest danger is threatening one of our most majestic, iconic of species, the sweet chestnut (Castanea sativa). So what exactly is this disease, how serious is the threat it poses, and what can we do to limit the danger?
Oriental chestnut gall wasp (Dryocosmus kuriphilus), has recently been discovered within our shores, in woodland in both Kent and Hertfordshire, and its arrival on our land poses a threat to substantial swathes of valuable habitat. The damage it inflicts is caused by the reproduction of a very small wasp. The insect itself is only 2.5 to 3.0mm long, and has a black body, with translucent wings and orange legs. Females lay their eggs in the buds of sweet chestnut trees, a process that triggers the formation of galls, abnormal growths on the leaves and branches of host trees. Larvae hatch from the eggs after a few weeks, before eating their way out of the galls as adults. The life span of these wasps is only around 10 days, with often half of that time spent emerging from the gall itself. Despite this prompt turn around, the empty galls can then remain on the trees for up-to two years, growing harder as they age. These galls have previously been shown to weaken the host tree, making it vulnerable to other pests and diseases, as well as reducing nut and timber production.
Previously, attempts to prevent the arrival of Oriental chestnut gall wasp to Britain have been strict, with inspection of sweet chestnut awaiting importation along with frequent monitoring of existing woodland and tree nurseries. Its breakthrough appearance however, will now be difficult to contain, with each female capable of laying 100 eggs in her short life-time. As a parthenogenetic species, the females do not require the presence of males to lay fertilised eggs, enabling such accelerated rates of reproduction. The Forestry Commission is now tasked with the formidable task of attempting to contain any outbreak and minimise the threat it poses, no mean feat. At present, there is no fully effective method established for its removal, but previously a mixture of pruning, destruction of infected trees, and pesticide use have show good success rates in combating its spread.
In the short time since Oriental chestnut gall was discovered, the most badly infected trees have already been destroyed, with guidance and advice being offered to relevant parties and woodland owners. However, the public are also being urged to do their bit to avoid widespread spread of this pest. Visitors to affected areas are urged to avoid picking up or carrying any tree material, and children are asked not to pick up or play with any galls they might find.
The coming weeks and months will be crucial in the race to contain the infection, and to see whether the current techniques deployed to control its spread, are effective or not. In the meantime, if you are at all concerned about the infection of trees on your property, or their general health, contact a trained arboriculturist for more information.
PJC Consultancy can provide you with a rage of arboricultural services including advice on tree health and disease. For more information from a fully qualified member of the team please fell free to contact us.