Confirming exactly what agents are causing horse chestnut bleeding canker is critical to any recommendations about effective control measures. Before embarking on any control measures on sites where there is a significant number of horse chestnuts, a survey to assess the number of affected trees is recommended.
There is no chemical treatment currently available to cure or arrest the development of bleeding canker:

Advice on the best time of year to prune is given in Arboriculture Note 117 (Lonsdale, 1993).  However, many trees with trunk infections retain healthy-looking crowns and may not pose an immediate safety risk. Some may even survive for many years as disease progression can be very slow or even cease, and show signs of recovery as vigorous callus development occurs at the margins of wounds created when bark has been killed by the disease.

Two cases of a new pathogen that could seriously affect trees have been found in native English oak (Quercus robur) trees in a wood near Redruth in Cornwall. This is the first discovery of fungal disease caused by this Phytophthora species in native oak trees in Britain.

The pathogen, is related to Phytophthora ramorum, known in the USA as Sudden Oak Death because of the widespread blight it has caused on American oak species. However, until now, native British oaks have proved to be resistant to both pathogens. Since the first discovery of P. ramorum in Britain early in 2002, neither laboratory tests nor painstaking surveys of more than 1500 woodland and forest sites across Britain have established any susceptibility of native oak trees to the deadly fungus.

Although P. ramorum is known to exist in more than a dozen countries throughout Europe, the new Phytophthora is so far thought to be specific to Britain. A major concern is that laboratory tests and observations in the wild indicate that it is more aggressive, and much faster spreading, than P. ramorum. Rhododendron, the main host and source of infection, succumbs in just a few weeks, rather than months.