Sycamore Leaf Spot
Each year we receive a number of calls from people concerned that sycamores appear to be dying. This is usually due to Grey Squirrel damage where the squirrels strip the bark off shoots and branches, girdling them and then the branch wilts and dies. This can look a little like elm disease with fiery red foliage on branch and tree tips.
However some years the main symptoms and cause are different. Leaves in the lower crowns of trees dry and fall early. This can be widespread within the lower crown rather than the extreme ends of shoots and the leaves fade rather than change colour. If you look closely at affected leaves you will see light grey spots rather like paint splash. The cause is a fungus Cristulariella depraedans. It normally occurs infrequently but occasionally there are epidemics when it becomes widespread and causes moderate amounts of defoliation.
NB Black spots on the leaves are caused by another common but relatively harmless Tar Spot fungus (Rhytisma acerinum)
In Cornwall in recent years we have seen more of this disease than normal probably due to the mild damp summers. Although the disease can look unsightly and defoliation can appear widespread, it is not a significant disease problem because the damage occurs late in the season after the main growth. All affected trees should come into leaf the following spring as normal. The level of disease declines in hot dry summers.
Further information can be found in Path News 15 (October 2007) produced by Forest Research.