An Invasive Pest in Farningham Woods

by Margaret Willis.

Coppiced chestnuts in Farningham Woods, 29 September 2016. Photo by Margaret Willis.

Those who know Farningham Woods but haven't been there lately are in for a big surprise, not to say a shock, if they visit the reserve now. An invasive pests has got there - the Oriental (Asian) Chestnut Gall Wasp Dryocosmus kuriphilus, first discovered by a Kent Field Club member on a field trip in May 2015. It seems that this was the first find in Britain but it has since been discovered in sites all over London and the South East, including Beckenham.

Chippings and fungi in Farningham Woods, 29 September 2016. Photo by Margaret Willis.

The wasp attacks the buds, leaves and petioles. It is described as a low impact pest but it can gradually weaken the tree and make it vulnerable to other problems such as the fungus Cryphonectria parasitica. The adult wasp is tiny, 2.5 - 3mm. and is unlikely to be seen by most visitors. It has a black body and orange legs. It is parthogenetic, ie it reproduces without the help of a male.

Gymnopilus dilepis in Farningham Woods, 29 September 2016. Photo by Margaret Willis.

Farningham Woods seems to have been the centre of an experiment to control this pest; 4 hectares of Sweet Chestnut wood (out of a Reserve total of 79 hectares) have been felled and the work is set to continue. Large numbers of wasps were noted on the trees and on the coppice regrowth in May 2016.

Pluteus petasatus in Farningham Woods, 29 September 2016. Photo by Margaret Willis.

The felling was started before the adults laid their eggs in early July. The aim is to slow down the spread of the wasp.

So if you go to the southern part of the wood you find a huge area of coppice with large stacks of cut timber and a huge pile of woodchips at the bottom.

An interesting bonus is the appearance of two rare fungi which like wood chippings and mulch — Gymnopilus dilepis and Pluteus petasatus. It will be interesting to see the ground flora which appears next spring.