Phytophthora ramorum and congenerics threaten oaks and other plants worldwide

Abstract

Phytophthora ramorum, a microscopic pathogen belonging to Phylum Oomycota, has been causing sudden oak death in California forests for over 25 years. In the U.S., this pathogen primarily kills Quercus agrifolia (coast live oak) and other oaks in genus Quercus, section Lobatae, as well as Notholithocarpus densiflorus(tanoak); in the UK, Ireland and France, it also killsLarix kaempferi(Japanese larch) and causes stem cankers and/or foliar blight on a variety of native and non-native hosts including Fagus sylvatica(beech), Castanea sativa, (sweet chestnut), Q. falcata(southern red oak) and Q. rubra(northern red oak). In nurseries, the pathogen has been detected on popular ornamental plants (i,e., Rhododendronand Camellia), and eradication is mandated by quarantines in over 60 countries in Asia, Europe and North America. In the past several years the estimate of the number of trees killed by the pathogen in California, has increased 10 fold to over 50 million. The apparent increase in estimated mortality underlines both our increasingly sophisticated understanding of this pathogen’s effects as well as its continued spread and infection of trees in western North America. This paper summarizes gains in pathogen understanding, new developments in pathogen distribution and activity, management approaches and research progress since 2014. In many ways we have learned a lot about P. ramorum. However, in terms of tree mortality, recent developments suggest that we are just beginning to foresee its potential to alter landscapes.

Citation

Lee, C.A.; Frankel, S.J.; Rizzo, D.M. 2019. Phytophthora ramorum and congenerics threaten oaks and other plants worldwide. In: Proceedings of the 9^th International Oak Society Conference, October 21-24, 2018. International Oaks. 30: 349-356.