Phytophthora ramorum - The Food and Environment Research ...

5. Symptoms
5.1 Phytophthora ramorum – On ornamentals
Disease symptoms of P. ramorum vary depending on the host plant and include leaf blight, leaf and
shoot/stem lesions and shoot die-back. Other disease pathogens may produce similar symptoms to
those of P. ramorum so care must be taken with diagnosis. Viburnum tinus is a good example where
symptoms of P. ramorum are very similar to those of the leaf and stem pathogen Phoma exigua var.
viburnii. Also, other Phytophthora species can cause similar symptoms in Rhododendron, though prior
to P. ramorum, foliage infections were uncommon. Root infection by other Phytophthora species is a
common problem in Rhododendron.
Disease symptoms in gardens and woodlands are not necessarily the same as those on commercial
nurseries: a large, mature Camellia, Rhododendron or Viburnum may have different symptoms in a
garden situation to when grown as a young plant for sale in a pot. For example, infected Viburnum
exhibits more of a shoot tip die-back rather than the very visible basal collapse more commonly seen
with potted plants.
Symptoms due to fertiliser scorch, chemical (e.g. pesticide) injury, drought stress, freezing damage
and sun scorch can also appear similar to P. ramorum infection on a range of hosts. Laboratory
analysis is required for accurate diagnosis.
Rhododendron die-back
Infected Rhododendron bush next to an infected holm
oak (Q. ilex)
Infected re-growth from a Rhododendron stump
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