Abstract The European Commission submitted to the EFSA Panel on Plant Health a Dossier from the United States proposing the use of a vacuum–steam–heat treatment as a stand‐alone phytosanitary measure to mitigate the risk of entry of Bretziella fagacearum, Geosmithia morbida and its vector Pityophthorus juglandis (thousand cankers disease complex) into the EU when trading oak (Quercus alba, Q. rubra) and walnut (Juglans nigra) logs with bark from the US. The proposed treatment consists of heating the sapwood to 56°C for 30 min at a depth of 5 cm from the cambium under vacuum and steam conditions. EFSA assessed the likelihood that logs of oak and walnut target species would be free from EU quarantine pests, basing its evaluation solely on the efficacy of the proposed treatment. In addition to B. fagacearum, G. morbida and P. juglandis, 14 other EU quarantine pests were identified as relevant because they are present in the US and are potentially associated with the commodities. The assessment was based on the information provided by the applicant country and on systematic literature reviews conducted by EFSA to determine the survival temperature and wood colonisation depth of the target pests. The evidence gathered was evaluated through an Expert Knowledge Elicitation (EKE) to estimate the likelihood of pest freedom of logs after the treatment assuming that all logs were infested. The vacuum–steam–heat treatment substantially reduces the presence of target pests infesting the sapwood. The EKE indicated with 95% certainty that between 9021 and 10,000 treated Q. alba logs per 10,000 and that between 9347 and 10,000 treated Q. rubra logs per 10,000 will be free from B. fagacearum. The EKE indicated with 95% certainty that between 9862 and 10,000 treated J. nigra logs per 10,000 will be free from G. morbida and that between 9948 and 10,000 treated J. nigra logs per 10,000 will be free from P. juglandis. However, the treatment is expected to be much less effective against pests which infest wood deeper than 5 cm from the cambium such as the species Arrhenodes minutus. The EKE indicated with 95% certainty that between 1109 and 10,000 logs per 10,000 will be free from A. minutus.

Global increases in connectivity have greatly accelerated the frequency of biological invasions across most of Earth’s ecosystems, including forests. Once invasive organisms become established in a naïve environment, they are difficult to eradicate or contain; thus, management strategies often focus on mitigating their impacts. As the use of chemical pesticides in forests is increasingly prohibited, biological control of pests and diseases has gained importance as an environmentally friendly alternative. Virus-mediated hypovirulence in the chestnut blight fungus Cryphonectria parasitica is one of the few successful examples of biological control of an invasive forest pathogen. However, experiments testing the stability of this system in situ are still missing. In this study, we conducted a field experiment in chestnut stands with naturally established hypovirulence in Switzerland, Croatia, and North Macedonia to evaluate the effectiveness of CHV1-mediated biocontrol of chestnut blight under different vegetative compatibility (vc) type population structures. Our results demonstrate that CHV1 is highly effective as a biological control agent against C. parasitica. Artificially initiated bark cankers of various vc types were rapidly infected by resident CHV1 strains, which significantly reduced canker growth and sporulation, thereby increasing the survival chances of the infected chestnut sprouts. Under field conditions, vegetative incompatibility barriers proved to be far less restrictive for virus transmission than predicted in vitro. Furthermore, our study demonstrates that the immigration of new fungal genotypes into existing cankers is an inherent component of the epidemiology of C. parasitica, which significantly contributes to the spread of CHV1. These results are particularly favourable for ensuring the success of hypovirulence-mediated biocontrol of chestnut blight in Europe. However, our conclusions cannot be automatically translated to genetically distant vc types from outside Europe, whose accidental introduction should be further avoided.

Abstract The European Commission requested the EFSA Panel on Plant Health to prepare and deliver risk assessments for commodities listed in Commission Implementing Regulation (EU) 2018/2019 as ‘High risk plants, plant products and other objects’. This Scientific Opinion covers plant health risks posed by unrooted cuttings of Salix species (S. aegyptiaca, S. eriocephala, S. gmelinii, S. miyabeana, S. purpurea, S. rehderiana, S. schwerinii, S. udensis, S. viminalis) imported from the United Kingdom (UK). The assessment was performed considering the available scientific information, including the technical information provided by the UK. All pests potentially associated with the commodities were evaluated against specific criteria. Only two EU Regulated pests (the fungus Entoleuca mammata and the oomycete Phytophthora ramorum (non‐EU isolates)), present in the UK and potentially associated with the commodity, were considered as relevant for this Opinion. No pests non‐regulated in the EU were identified to be selected for further evaluation.

Abstract The European Commission requested the EFSA Panel on Plant Health to prepare and deliver risk assessments for commodities listed in Commission Implementing Regulation (EU) 2018/2019 as ’High‐risk plants, plant products and other objects'. This Scientific Opinion covers plant health risks posed by Acer plants (A. griseum, A. platanoides, A. rubrum, A. saccharum, A. saccharinum, A. tataricum and A. tataricum subsp. ginnala, Acer × freemani) imported from Ukraine as dormant plants: (a) 1–4 years old bare root plants and (b) 1–2 years old plants in pots, taking into account the available scientific information, including the technical information provided by Ukraine. All pests associated with the commodity were evaluated against specific criteria for their relevance for this opinion. Two EU protected zone quarantine pests, i.e. Cryphonectria parasitica, and Entoleuca mammata and one EU‐quarantine pest, i.e. Lopholeucaspis japonica fulfilled all relevant criteria and were selected for further evaluation. For the selected pests, the risk mitigation measures proposed in the technical dossier from Ukraine were evaluated taking into account the possible limiting factors. For the selected pests an expert judgement is given on the likelihood of pest freedom taking into consideration the distribution of the pest in Ukraine, risk mitigation measures acting on the pest and uncertainties associated with the assessment. The degree of pest freedom varies among the pests evaluated, with L. japonica being the pest most frequently expected on imported plants. The Expert Knowledge Elicitation (EKE) indicated with 95% certainty that between 9748 and 10,000 per 10,000 bare root 1–4 years old plants will be free from L. japonica.

The European Commission requested the EFSA Panel on Plant Health to deliver a risk assessment on the likelihood of pest freedom from regulated EU quarantine pests, with emphasis on Bursaphelenchus xylophilus and its vectors Monochamus spp. of debarked conifer wood chips fumigated with sulfuryl fluoride as proposed by the United States (US) and as outlined in ISPM 28 - PT23 of sulfuryl fluoride (SF) fumigation treatment for nematodes and insects in debarked wood. The assessment considered the different phases in the wood chips' production, with special emphasis on the SF treatment. In addition to B. xylophilus and its vectors Monochamus spp., 22 EU quarantine pests and protected zone quarantine pests, some of which are regulated as groups of pests by the Commission Implementing Regulation (EU) 2019/2072, are present in the US and are potentially associated with the commodity. For these pests an expert judgement is given on the likelihood of pest freedom taking into consideration the available scientific information and technical information provided by the US, including uncertainties associated with the assessment. The likelihood of pest freedom varies among the pests evaluated, with B. xylophilus being the pest most frequently expected on the commodity. The Expert Knowledge Elicitation (EKE) indicated with 95% certainty that between 9491 and 10,000 m3 of debarked conifer wood chips treated with SF per 10,000 m3 will be free from B. xylophilus, and that between 9987 and 10,000 m3 of wood chips per 10,000 m3 will be free from Monochamus spp. Technical elements which are critical for a successful treatment and for minimising the presence of Union quarantine pests on the commodity are identified and described in the opinion. In particular, it is important to note that SF treatments are generally less effective in eliminating fungi than insects, the required parameters of the fumigation should be met at all points of the pile of wood chips and the time of storage of wood chips before treatment should be kept as short as possible because B. xylophilus can easily reproduce and spread throughout the pile under conducive conditions.

Cryphonectria carpinicola, the most recently described species in the genus Cryphonectria, is gaining research interest due to its involvement in common hornbeam (Carpinus betulus) decline. So far, no symptoms of hornbeam decline have been observed in Croatian forests. However, following a chance observation of a Cryphonectria-like stromata on the bark of a dead hornbeam branch, we conducted a targeted sampling campaign to verify the presence of C. carpinicola, determine its distribution and assess its potential impact on the host. We confirmed the presence of C. carpinicola in four out of five sampled populations and isolated pure cultures from 28 out of 53 sampled trees, making it the largest collection of C. carpinicola in Europe to date. The population network analysis inferred from nucleotide sequences of C. carpinicola ITS region, including this and previous research, has grouped them all in a single cluster with only a few isolates differing by a single nucleotide polymorphism. The isolation of C. carpinicola was possible only from bark samples with visible sporulation. The majority (24) of C. carpinicola isolates were obtained from dead stems or branches. However, in two different populations, we isolated the fungus from branches on four living trees that had died off distally to the area of the observed fungal sporulation, suggesting the fungus to be at least a weak pathogen on susceptible hornbeam trees.

The European Commission requested the EFSA Panel on Plant Health to prepare and deliver risk assessments for commodities listed in Commission Implementing Regulation (EU) 2018/2019 as 'High risk plants, plant products and other objects'. This Scientific Opinion covers plant health risks posed by plants of Populus alba, Populus nigra and Populus tremula imported from the United Kingdom (UK) as: (a) 1- to 7-year-old bare root plants, (b) 3- to 15-year-old plants in pots, (c) 1- to 2-year-old cell grown plants and (d) bundles of 1- to 2-year-old cuttings/graftwood (only for P. nigra and P. tremula), taking into account the available scientific information, including the technical information provided by the UK. All pests associated with the commodity were evaluated against specific criteria for their relevance for this Opinion. Two EU protected zone quarantine pests, i.e. Bemisia tabaci (European populations) and Entoleuca mammata, fulfilled all relevant criteria and were selected for further evaluation. For the selected pests, the risk mitigation measures implemented in the technical dossier from the UK were evaluated taking into account the possible limiting factors. Expert judgements were given on the likelihood of pest freedom taking into consideration the risk mitigation measures acting on the pest, including uncertainties associated with the assessment. The age of the plants was considered, reasoning that older trees are more likely to be infested mainly due to longer exposure time and larger size. The degree of pest freedom varies between the pests evaluated, with E. mammata being the pest most frequently expected on the imported plants. The Expert Knowledge Elicitation (EKE) indicated with 95% certainty that between 9730 and 10,000 per 10,000 P. tremula rooted plants in pots (3 to 15 year old) will be free from E. mammata.

The European Commission requested the EFSA Panel on Plant Health to prepare and deliver risk assessments for commodities listed in Commission Implementing Regulation (EU) 2018/2019 as 'High risk plants, plant products and other objects'. This Scientific Opinion covers plant health risks posed by plants of Taxus baccata imported from the United Kingdom (UK) as: (a) bundles of 2-year-old bare root plants (whips), (b) 2- to 7-year-old bare root plants, either exported as single plants or in bundles, (c) 2-year-old cell grown plants exported in bundles, and (d) 3- to 15-year-old plants in pots. The assessment was performed considering the available scientific information, including the technical information provided by the UK. All pests associated with the commodity were evaluated against specific criteria for their relevance for this opinion. One EU quarantine pest, Phytophthora ramorum (non-EU isolates) fulfilled all relevant criteria and was selected for further evaluation. For the selected pest, the risk mitigation measures implemented in the technical dossier from the UK were evaluated taking into account the possible limiting factors. An expert judgement was given on the likelihood of pest freedom taking into consideration the risk mitigation measures acting on the pest, including uncertainties associated with the assessment. The fact that T. baccata is an evergreen plant on which P. ramorum can cause foliar infection was considered a critical element in the risk assessment. In addition, the age of the plants was considered, reasoning that older trees are more likely to be infected mainly due to longer exposure time and larger size. The degree of pest freedom slightly differs between bare root plants (including whips) and plants in pots (including cell grown plants), with plants in pots being less likely pest free. The Expert Knowledge Elicitation (EKE) indicated with 95% certainty that between 9699 and 10,000 3- to 15-year-old plants in pots and bundles of 2-year-old cell grown plants per 10,000 will be free from P. ramorum (non-EU isolates).

The European Commission requested the EFSA Panel on Plant Health to prepare and deliver risk assessments for commodities listed in Commission Implementing Regulation (EU) 2018/2019 as 'High risk plants, plant products and other objects'. This Scientific Opinion covers plant health risks posed by plants of Salix caprea and Salix cinerea imported from the United Kingdom (UK) as: (a) bundles of 1- to 2-year old cuttings/graftwood, (b) 1- to 7-year-old bare root plants, (c) 1- to 2-year-old cell grown plants and (d) 2- to 15-year-old plants in pots, taking into account the available scientific information, including the technical information provided by the UK. All pests associated with the commodities were evaluated against specific criteria for their relevance for this opinion. Two EU protected zone quarantine pests, i.e. Bemisia tabaci (European populations) and Entoleuca mammata, and one EU quarantine pest, i.e. Phytophthora ramorum (non-EU isolates), fulfilled all relevant criteria and were selected for further evaluation. For the selected pests, the risk mitigation measures described in the technical dossier from the UK were evaluated. Expert judgements were given on the likelihood of pest freedom taking into consideration the risk mitigation measures acting on the pests, including uncertainties associated with the assessment. The age of the plants was considered, reasoning that older trees are more likely to be infested mainly due to longer exposure time and larger size. The degree of pest freedom varies between the pests evaluated, with P. ramorum being the pest most frequently expected on the imported plants. The Expert Knowledge Elicitation (EKE) indicated with 95% certainty that between 9738 and 10,000 rooted S. caprea and S. cinerea plants in pots (2 to 15-year-old) per 10,000 will be free from P. ramorum.

The remarkable speed at which viral populations mutate allows them to evolve quickly, so that the viral diversity can change, especially when the virus is transmitted, i.e. its population goes through a bottleneck. Our experiments assessed the diversity of the intra-host populations of a mycovirus Cryphonectria hypovirus 1 (CHV1), a natural biocontrol agent of chestnut blight disease, using PacBio long-read HiFi sequencing. The intra-host viral population diversity before and after either vertical or horizontal transmission was estimated using two metrics-nucleotide (mutational) diversity measured as π, and viral variant diversity measured as Nei's H. A significant bottleneck effect, demonstrated by the decline of the mutational diversity (π), was observed after vertical transmission of prototypical viral populations into conidia, in both investigated viral subtypes, French 1 (F1) and Italian (I). In contrast, the number of viral variants was significantly reduced after the vertical transmission of subtype I but increased for the subtype F1. In newly isolated fungal strains infected with CHV1 subtype I, fewer viral variants were vertically transferred into conidia, relative to the prototypical laboratory isolates, i.e. the average number of transmitted viral variants was smaller. In the horizontal viral transmission assays, the number of transmitted viral variants was closely linked to the genotype of the fungal host at the vegetative compatibility loci. Specifically, recipient viral populations' diversity was greater when the alleles at loci vic2 and vic3 were the same in the donor and recipient fungal isolate, relative to when they were different. Heteroallelism at the vic4 locus had no impact on viral populations' diversity. Despite the strong bottlenecks, purifying selection shaped the diversity of intra-host CHV1 populations. In both transmission experiments on average, synonymous mutational diversity was higher than non-synonymous, across all replicates. Signs of positive selection or mutation accumulations, inferred by a surplus of nonsynonymous mutations, were less common and mostly observed during vertical transmission experiments, i.e. in new viral populations arising from conidia.

The European Commission requested the EFSA Panel on Plant Health to prepare and deliver risk assessments for commodities listed in Commission Implementing Regulation (EU) 2018/2019 as 'High risk plants, plant products and other objects'. This Scientific Opinion covers plant health risks posed by plants of Tilia cordata and T. platyphyllos imported from the United Kingdom (UK) as: (a) bundles of budwood/graftwood; (b) 1- to 2-year-old whips, seedlings or transplants; (c) bundles of 1- to 2-year-old cell grown plants; (d) 1- to 7-year-old bare root single plants; and (e) up to 25-year-old single plants in pots, taking into account the available scientific information provided by the UK. A list of pests potentially associated with the commodities was compiled. The relevance of any pest was assessed based on evidence following defined criteria. None of the pests on the list fulfilled all relevant criteria and therefore none were selected for further evaluation. As a result, risk mitigation measures proposed in the technical dossier from the UK were listed, but not further evaluated.

Invasive fungal diseases represent a major threat to forest ecosystems worldwide. As the application of fungicides is often unfeasible and not a sustainable solution, only a few other control options are available, including biological control. In this context, the use of parasitic mycoviruses as biocontrol agents of fungal pathogens has recently gained particular attention. Since the 1990s, the Asian fungus Hymenoscyphus fraxineus has been causing lethal ash dieback across Europe. In the present study, we investigated the biocontrol potential of the mitovirus Hymenoscyphus fraxineus mitovirus 2 (HfMV2) previously identified in Japanese populations of the pathogen. HfMV2 could be successfully introduced via co-culturing into 16 of 105 HfMV2-free isolates. Infection with HfMV2 had contrasting effects on fungal growth in vitro, from cryptic to detrimental or beneficial. Virus-infected H. fraxineus isolates whose growth was reduced by HfMV2 showed overall a lower virulence on ash (Fraxinus excelsior) saplings as compared with their isogenic HfMV2-free lines. The results suggest that mycoviruses exist in the native populations of H. fraxineus in Asia that have the potential for biological control of ash dieback in Europe. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

The European Commission requested the EFSA Panel on Plant Health to prepare and deliver risk assessments for commodities listed in Commission Implementing Regulation (EU) 2018/2019 as 'High risk plants, plant products and other objects'. This Scientific Opinion covers plant health risks posed by plants of Corylus avellana imported from the United Kingdom (UK) as: (a) bundles of 1- to 2-year old whips or transplants, (b) bundles of 1- to 2-year old cell grown plants, (c) 1- to 7-year old bare root single plants and (d) up to 15-year old single plants in pots, taking into account the available scientific information, including the technical information provided by the UK. All pests associated with the commodity were evaluated against specific criteria for their relevance for this opinion. Two EU quarantine pests, Phytophthora ramorum (non-EU isolates) and Thaumetopoea processionea fulfilled all relevant criteria and were selected for further evaluation. For the selected pests, the risk mitigation measures implemented in the technical dossier from the UK were evaluated taking into account the possible limiting factors. For these pests an expert judgement is given on the likelihood of pest freedom taking into consideration the risk mitigation measures acting on the pest, including uncertainties associated with the assessment. In the assessment of risk, the age of the plants was considered, reasoning that older trees are more likely to be infested mainly due to longer exposure time and larger size. The degree of pest freedom varies among the pests evaluated, with P. ramorum being the pest most frequently expected on the imported plants. The expert knowledge elicitation indicated with 95% certainty that between 9939 and 10,000 of the single plants in pots up to 15-year old will be free from P. ramorum (non-EU isolates).

The European Commission requested the EFSA Panel on Plant Health to prepare and deliver risk assessments for commodities listed in Commission Implementing Regulation (EU) 2018/2019 as 'High risk plants, plant products and other objects'. This Scientific Opinion covers plant health risks posed by plants of the evergreen Ligustrum ovalifolium and the semi-evergreen Ligustrum vulgare imported from the United Kingdom (UK) as: (a) bare root plants and (b) plants in pots, taking into account the available scientific information, including the technical information provided by the UK. The category (a) 'bare root plants' includes bundles of 1- to 3-year-old bare root whips or transplants and single 1- to 7-year-old bare root plants. The category (b) 'plants in pots' includes bundles of 1- to 2-year-old cell grown plants (only L. vulgare) and 1- to 5-year-old plants in pots. All pests associated with the commodities were evaluated against specific criteria for their relevance for this opinion. Two EU quarantine pests, Bemisia tabaci and Scirtothrips dorsalis, and one pest not regulated in the EU, Diaprepes abbreviatus, fulfilled all relevant criteria and were selected for further evaluation. For the selected pests, the risk mitigation measures proposed in the technical dossier from the UK were evaluated taking into account the possible limiting factors. For these pests, an expert judgement is given on the likelihood of pest freedom considering the risk mitigation measures acting on the pest, including uncertainties associated with the assessment. In the assessment of risk, the age of the plants was considered, reasoning that older trees are more likely to be infested mainly due to longer exposure time and larger size. The degree of pest freedom varies among the pests evaluated, with B. tabaci being the pest most frequently expected on the imported plants. The Expert Knowledge Elicitation indicated with 95% certainty that between 9915 and 10,000 per 10,000 bare root plants and plants in pots will be free from B. tabaci.

Abstract The European Commission requested the EFSA Panel on Plant Health to prepare and deliver risk assessments for commodities listed in Commission Implementing Regulation (EU) 2018/2019 as ‘High risk plants, plant products and other objects’. This Scientific Opinion covers plant health risks posed by plants of Betula pendula and B. pubescens imported from the United Kingdom (UK) taking into account the available scientific information, including the technical information provided by the UK. The commodities were grouped in the risk assessment as (a) bundles of 10–20 graftwood/budwood (up to 1‐year‐old), (b) bare root plants which include bundles of 25 or 50 seedlings or transplants (1–2 years‐old), bundles of 5, 10 or 15 whips (1–2 years‐old) and single bare root plants (1–7 years‐old), (c) plants in pots which include bundles of 5 and 10 cell‐grown plants (1–2 years‐old) and rooted plants in pots (1–7 years‐old), and (d) large specimen trees up to 15‐years‐old. All pests associated with the commodities were evaluated against specific criteria for their relevance for this opinion. Two EU quarantine pests i.e. Meloidogyne fallax and Phytophthora ramorum (non‐EU isolates) and two protected zone quarantine pests i.e. Entoleuca mammata and Thaumetopoea processionea fulfilled all relevant criteria and were selected for further evaluation. For the selected pests, the risk mitigation measures described in the technical dossier from the UK were evaluated considering the possible limiting factors. For these pests an expert judgement is given on the likelihood of pest freedom taking into consideration the risk mitigation measures acting on the pest, including uncertainties associated with the assessment. In the assessment of risk, the age of the plants was considered, as larger trees are more likely to be infested mainly due to longer time grown in the field. In addition, larger canopies and root systems are more difficult to inspect, thereby making the detection of pests more challenging on large trees. The likelihood of pest freedom varies among the pests evaluated, with M. fallax being the pest most frequently expected on the imported plants. The Expert Knowledge Elicitation (EKE) indicated with 95% certainty that between 9735 and 10,000 per 10,000 large specimen trees will be free from M. fallax.

The European Commission requested the EFSA Panel on Plant Health to deliver a risk assessment on the likelihood of pest freedom from Union quarantine pests and pests subject to measures adopted pursuant to Article 30 of Regulation (EU) No 2016/2031 for the maple veneer sheets manufactured according to the process set out by Canada, with emphasis on the freedom from Davidsoniella virescens and Phytophthora ramorum (non-EU isolates). The assessment was conducted for veneer sheets of up to 0.7 mm and up to 6 mm thickness, taking into account the different phases in the veneer production in a systems approach. Some of those phases, taken alone, including the heat treatment of logs in a water bath, the cutting into thin veneer sheets and the final high heat drying of veneer sheets are expected to be effective against some of the pests, without uncertainties, making the system approach fully effective. The panel considers that no insects would survive cutting of logs into thin veneer sheets of 0.7 mm and that Xylella fastidiosa will not survive the temperatures in the water bath and final drying of veneers. The degree of pest freedom for the different groups of organisms is generally very high with slightly lower degree of pest freedom for veneer sheets of 6 mm thickness because of lower temperatures reached in the final drying of veneer sheets compared to thinner sheets. P. ramorum is not expected to survive the high heat drying of thin veneer sheets, but it may survive the lower temperatures inside thicker veneer sheets. The Expert Knowledge Elicitation (EKE) indicated, with 95% certainty, that between 9989 and 10,000 veneer sheets (thickness 6 mm) per 10,000 will be free from living P. ramorum. For D. virescens, the EKE indicated, with 95% certainty, that between 9984 and 10,000 veneer sheets (0.7 mm) per 10,000 and that between 9954 and 10,000 veneer sheets (6 mm) per 10,000 will be free from living inoculum. For other relevant groups of pests, the greatest likelihood of pest presence was observed for wood decay fungi. The EKE indicated, with 95% certainty, that between 9967 and 10,000 veneer sheets (0.7 mm) per 10,000 and that between 9911 and 10,000 veneer sheets (6 mm) per 10,000 will be free from living wood decay fungi.

Phytophthora species are a cause for concern due to their invasive potential and the damage they can cause in agriculture, forestry, and natural ecosystems worldwide. Since water plays a crucial role in their dispersal, stream and river baiting is commonly used to survey risk areas for the presence of quarantine Phytophthora species. However, our understanding of the distribution and diversity of Phytophthora species in European watercourses remains incomplete. This study investigated the presence and diversity of Phytophthora species in Swiss watercourses, with a focus on the highly urbanized Swiss Plateau. Over the period 2012–2016, we sampled 32 watercourses, including major rivers and smaller streams. We isolated Phytophthora on selective media and sequenced the internal transcribed spacer region to identify the species. We recovered 241 Phytophthora isolates, representing 11 species from five major clades. Phytophthora clade 6 prevailed, with P. lacustris being the most common, found in 94.7% of the watercourses. The number of Phytophthora species per watercourse ranged from one to five, with no correlation to watercourse complexity. Our study reveals the presence of six previously unreported species in Switzerland, while known invasive species were not found. Watercourses appear less suited to detect invasive pathogenic Phytophthora species with a still limited distribution in the environment.

The European Commission requested the EFSA Panel on Plant Health to prepare and deliver risk assessments for commodities listed in Commission Implementing Regulation (EU) 2018/2019 as 'High risk plants, plant products and other objects'. This Scientific Opinion covers plant health risks posed by plants of Acer pseudoplatanus imported from the United Kingdom (UK) as: (a) 1- to 7-year-old bare root plants for planting, (b) 1- to 7-year-old plants in pots and (c) bundles of 1- to 2-year-old whips and seedlings, taking into account the available scientific information, including the technical information provided by the UK. All pests associated with the commodity were evaluated against specific criteria for their relevance for this opinion. Six EU quarantine pests and four pests not regulated in the EU fulfilled all relevant criteria and were selected for further evaluation. For these pests, the risk mitigation measures implemented in the technical dossier from the UK were evaluated taking into account the possible limiting factors. For the selected pests, an expert judgement is given on the likelihood of pest freedom taking into consideration the risk mitigation measures acting on the pest, including uncertainties associated with the assessment. The degree of pest freedom varies among the pests evaluated, with Meloidogyne mali or M. fallax being the pest most frequently expected on the imported plants. The Expert Knowledge Elicitation indicated with 95% certainty that 9,792 or more plants in pots per 10,000 will be free from Meloidogyne mali or M. fallax.

The sooty bark disease (SBD) is an emerging disease affecting sycamore maple trees (Acer pseudoplatanus) in Europe. Cryptostroma corticale, the causal agent, putatively native to eastern North America, can be also pathogenic for humans causing pneumonitis. It was first detected in 1945 in Europe, with markedly increasing reports since 2000. Pathogen development appears to be linked to heat waves and drought episodes. Here, we analyse the conditions of the SBD emergence in Europe based on a three-decadal time-series data set. We also assess the suitability of aerobiological samples using a species-specific quantitative PCR assay to inform the epidemiology of C. corticale, through a regional study in France comparing two-year aerobiological and epidemiological data, and a continental study including 12 air samplers from six countries (Czechia, France, Italy, Portugal, Sweden and Switzerland). We found that an accumulated water deficit in spring and summer lower than -132 mm correlates with SBD outbreaks. Our results suggest that C. corticale is an efficient airborne pathogen which can disperse its conidia as far as 310 km from the site of the closest disease outbreak. Aerobiology of C. corticale followed the SBD distribution in Europe. Pathogen detection was high in countries within the host native area and with longer disease presence, such as France, Switzerland and Czech Republic, and sporadic in Italy, where the pathogen was reported just once. The pathogen was absent in samples from Portugal and Sweden, where the disease has not been reported yet. We conclude that aerobiological surveillance can inform the spatial distribution of the SBD, and contribute to early detection in pathogen-free countries.

The European Commission requested the EFSA Panel on Plant Health to prepare and deliver risk assessments for commodities listed in Commission Implementing Regulation (EU) 2018/2019 as ‘High risk plants, plant products and other objects’. This Scientific Opinion covers plant health risks posed by plants of Acer campestre imported from the UK as: (a) 1- to 7-year-old bare root plants for planting, (b) 1- to 15-year-old plants in pots and (c) bundles of 1- to 2-year-old whips and seedlings, taking into account the available scientific information, including the technical information provided by the UK. All pests associated with the commodity were evaluated against specific criteria for their relevance for this opinion. Six EU quarantine pests and four pests not regulated in the EU fulfilled all relevant criteria and were selected for further evaluation. For the selected pests, the risk mitigation measures implemented in the technical dossier from the UK were evaluated taking into account the possible limiting factors. For these pests, an expert judgement is given on the likelihood of pest freedom taking into consideration the risk mitigation measures acting on the pest, including uncertainties associated with the assessment. In the assessment of risk, the age of the plants was considered, reasoning that older trees are more likely to be infested mainly due to longer exposure time and larger size. The degree of pest freedom varies among the pests evaluated, with Phytophthora ramorum being the pest most frequently expected on the imported plants. The expert knowledge elicitation indicated with 95% certainty that 9,757 or more 1- to 15-year-old plants in pots per 10,000 will be free from P. ramorum.