Those prone to nervous anxiety should stay away from the July issue of the Quarterly Journal of Forestry. It describes a new disease affecting gardens in Cornwall. What is known in America as Sudden Oak Death has been flagged as a threat here for the past five years. The new find is another strain of Phytophthora all too well adapted to
destroying Cornwall’s precious trees and shrubs.
Phytophthora kernoviae takes its name from Kernow, the old name for Cornwall. It loves Cornwall’s jungle conditions where big-leaved rhododendrons and magnolias thrive, spreading through mist and water-drops where breezes rarely stir. Eighty Cornish gardens have so far been infected, among them Trengwainton, where the National Trust has set up a monitoring station. Phytophthora there has already claimed magnolias, acacia, jasmines, rhododendrons and kalmias. In
other gardens camellias, viburnums and drimys have caught it. Worse, there are cases of beech (but not oak) being affected. Given the right conditions Phytophthora of two strains – kernoviae and the original Sudden Oak Death strain, ramorum – seem able to kill almost anything.
The conditions are specific, and rhododendrons are important hosts. R. ponticum, that ineradicable weed (however pretty its flowers) of broadleaved woodlands, harbours Phytophthora and passes it on. The precautions to take are to reduce the damp shade element, clearing undergrowth to let light and air in, to get rid of weak old wood and promote strong growth. Bleeding bark cankers are the
principal symptoms. None of it makes pretty reading.
With this year’s weather I had just been relishing the almost Cornish feel (at least for an Essex garden) of our establishing
woodland, the damp mulch and the dense foliage. For how much longer, I wonder.