Phytophthora – Slayer Of Trees

The annual survey of trees in 2012 showed a large number of deaths, or die-back, of alder trees. We have been advised that this is probably caused by Phytophthora Alni, a pathogen which affects the roots of the trees. Until recently this disease has been confined to Europe and southern England, but is now moving north.

Over the last 8 years we have planted some 4000 trees in copses on the course and about 500 of these have been alders, of which up to 100 are seen to be infected. The policy has been to plant mixed copses, so as not to depend on any one particular variety of tree. In general alders have done well on the course, being well adapted to the wet clayey conditions and growing quickly into a substantial tree of good shape.

The disease has three phases: firstly the top bends over and becomes contorted; then die-back starts at the ends of the branches, leading to near-death, the only growth being confined to shoots from the base of the tree: anything above this level is dead; finally the tree dies. There is no cure for the disease: all one can do is to coppice the tree so that it becomes a bush and hope that it will live.

Fortunately the disease does not spread to other species. It is thought that eventually all the alders on the course will be affected. However this may not be too serious as we are now reaching the stage when some of the mixed copses need thinning. On the other hand there are some copses, planted when the course was originally constructed, which consist solely of alders. Fortunately these are mostly Italian alders, which appear less vulnerable to the disease. However as an insurance against losing a whole copse it has been decided to interplant the existing trees with other species, such as hornbeam, which also do well in these conditions.

Where did the disease come from? Initial thoughts were that we had planted an infected batch, but this is difficult to prove as the disease has been found in all parts of the course and in all sizes of tree up to 400mm girth. An alternative is that Guy Lane Brook, the stream running through the course, is carrying the disease and that it has spread from this source. Several diseased trees have also been found alongside the River Gowy between Huxley and Tiverton, some 5 miles upstream of the course, so it may now be infecting a wider area. However, good growing conditions in 2013 meant that the disease has not developed further to date.