Horse Chestnut Disease hits Wiltshire

I wonder how many of you were aware that one of our grandest trees, the Horse Chestnut is under attack from an alien moth which is sweeping across Wiltshire?

The disease is caused by The Leaf Miner Moth (Cameraria ohridella) and was first identified in Macedonia in 1985, subsequently causing devastation to horse chestnuts across mainland Europe.

Since 2002 the disease has been sweeping across the UK from the South East and a recent survey has revealed how its effects are now being seen across Wiltshire: http://www.ourweboflife.org.uk/surveyresults.html

The moth lays its eggs in the leaves so that when the larvae hatch they eat and tunnel their way through the tissues of the leaves. The effects are all too obvious with the tell trail marks on the leaves of these majestic trees causing them to turning brown and wither. Over time this will seriously weaken the tree by preventing it to photosynthesise effectively so the tree starves to death.

Experts believe the effects of the disease could equal the devastation of the Elms 20 years ago.Forestry Research Scientists have estimated that some 35,000 to 50,000 trees are already infected and it is likely that many Horse Chestnuts are likely to be lost over the next decade.

Ongoing research by Dr Darren Evans of the University of Hull and Dr Michael Pocock of Bristolhave recently launched a study to try to discover just how big a problem is posed by the horse chestnut leaf miner. People across the UK are now being asked to help record the impact of the disease at http://www.ourweboflife.org.uk/

In my role as one of Tree Council's Tree Wardens I am keen to raise awareness of this disease so I am particularly pleased with Mike Wilkinson's coverage in this weeks Gazette and Herald: http://www.gazetteandherald.co.uk/news/8314574.Trees_in_Wiltshire_face_a_wipeout and also in the Wiltshire Times: http://www.wiltshiretimes.co.uk/news/8317822.Fears_for_Wiltshire_s_trees/

One surprising ray of hope comes from the increased presence of a parasitic wasp, which is the leaf miner's natural predator as its feeds on the Leaf Miner Larvae. There is apparently a time lag between the moth infesting a tree and the wasps attacking the caterpillars. So let's hope they catch up!

However, to make matters worse the Horse Chestnut is being subjected to a three pronged assault as it not only the leaf miners causing problems for these trees. The second threat comes from the Leaf Blotch Fungus (Guignardia aesculi) which attacks the leaves so that reddish or brown blotches with yellow borders develop. However, the most damaging condition seems to be Bleeding Canker the cause of which is a fungus-like organism - Phytophthora. Varieties of this disease are known to be responsible for attacking more than Horse Chestnuts, such as sudden Oak Death. I think I have also seen this on some of our trees around Corsham.