Assessment of the eradication measures applied to Phytophthora ramorum in Irish Larix kaempferi forests

Abstract

Summary Phytophthora ramorum is the causal agent of the sudden larch death epidemic in Ireland and the UK. Within the EU, it is a quarantine pathogen and eradication measures are required if it is detected in horticultural or forest environments. Eradication measures in forests include the clearance of susceptible tree hosts from the infected stand along with all host known to support pathogen sporulation within a 250‐m buffer zone of the infected stand. Between 2010 and 2016, these measures have affected over 18,000 ha of Larix kaempferi forests in Ireland and the UK, but the epidemic continues to spread. An assessment of the efficacy of the eradication measures has not been published to date. Here, we provide details of the detection frequency of P. ramorum from aerial (rainwater) and terrestrial (soil, watercourses, plant material) sources in three forest locations in Ireland that had significant areas of L. kaempferi affected by P. ramorum before their removal. Monitoring of six plots with differing infection and eradication management histories was carried out from September 2013 to 2015. Presence of P. ramorum was confirmed by plating plant material onto selective media, followed by morphological identification. Phytophthora ramorum was detected in 65 of 1283 samples, in all sample types and in 17 of the 20 months sampled. Only three of the 295 soil samples were positive for P. ramorum, with all of these coming from an area under perennial standing water. The most positive samples came from a plot where symptomatic Larix trees had not been removed and the findings occurred consistently over the 2‐year study. Plots where infected Larix had been removed were rarely positive for P. ramorum across all the sample types indicating a level of success from the eradication measures in reducing pathogen levels on the sites.

Canker and decline diseases caused by soil- and airborne Phytophthora species in forests and woodlands

“…data). In Northern Ireland, it was recently demonstrated that the felling and removal of larch trees significantly reduces the inoculum of P. ramorum in the soil and successfully eradicates the pathogen from infested sites ( O’Hanlon et al 2017 ). SLD has a serious impact on the UK larch industry.…”

Comparative Genomic and Proteomic Analyses of Three Widespread Phytophthora Species: Phytophthora chlamydospora, Phytophthora gonapodyides and Phytophthora pseudosyringae

“…The details of the isolates used in this study are provided in Table 1. Methods for the isolation of the isolates and tentative morphological identification have been reported previously [41,42]. Briefly, this involved plating the samples onto P 5 ARP[H] agar (Cornmeal agar with antibiotics [43]) and incubating at room temperature for two weeks.…”

Pathogenicity and infectivity of Phytophthora ramorum vary depending on host species, infected plant part, inoculum potential, pathogen genotype, and temperature

“…While infestations in commercial nurseries and in landscaped settings have been manageable using traditional disease management approaches (Tjosvold et al, 2005), infestations in natural ecosystems have been impossible to control due to their scale and intensity (Cunniffe et al, 2016;Rizzo et al, 2005). Infestations in larch plantations have been controlled, but with a huge cost and accepting significant losses (O'Hanlon et al, 2018). P. ramorum was the first generalist pathogen to be regulated at many national and international levels (Garbelotto and Rizzo, 2005).…”