Phytophthora ramorum on larch and chestnut in Western France
In France, Phytophthora ramorum (EPPO A2 List) was first detected in 2002 and was then only found in nurseries on Rhododendron spp. and Viburnum spp. Outbreaks in forest stands were first detected in May 2017 in two sites (Saint-Cadou and Hanvec) on Larix kaempferi (Japanese larch) in Finistère (Bretagne region, North-Western France) Eradication measures were applied (EPPO RS 2017/129). Surveys were conducted in 2018-2021 to assess the presence of P. ramorum in an area of 18 km radius around those outbreaks, as well as in the vicinity of seven ornamental nurseries that had been infected by P. ramorum in the past. Overall, a limited presence of P. ramorum was detected in 2018–2021. Only two new stands of infected L. kaempferi were found close to the main initial outbreak, in Saint-Cadou and Saint-Rivoal. The pathogen was only detected on rhododendrons and chestnut trees (Castanea sativa) in the vicinity of the outbreaks. In the Saint-Cadou forest, eradication measures were applied including the felling of all mature larch trees, however an outbreak of P. ramorum was found on chestnut trees. P. ramorum was also detected near two of the formerly infected ornamental nurseries, on C. sativa and on rhododendrons. The authors consider that the impact on chestnuts is the major risk of P. ramorum in France.
Sources
Beltran A, Laubray S, Ioos R, Husson C, Marçais B (2024) Low persistence of Phytophthora ramorum (Werres, De Cock, and Man in ‘t Veld) in western France after implementation of eradication measures. Annals of Forest Science 81(1), 7. https://doi.org/10.1186/s13595-024-01222-1