Oak decline is a complex disorder caused by multiple stressors. Although declines have been observed across Europe since 1700, there is still a lot of uncertainty around the cause, and therefore the appropriate management techniques. Using literature from across European oak ecosystems, this review and perspective discusses the key stressors associated with oak declines in Quercus robur L. and Q. petraea (Matt.) Liebl. in Europe and the newly described acute oak decline breaking out in the United Kingdom (and beyond), with a view to identifying important evidence gaps and management implications. The key factors implicated in oak decline include drought, pests and pathogens. These factors can interact in positive feedback loops to increase stress and decline within oaks. Extreme frost, waterlogging, soil properties, land management, nitrogen pollution, heavy metal pollution, genetic predisposition and mycorrhizal changes could also be involved in decline, but more research is required to understand these. In acute oak decline, necrotic lesions are caused by a bacterial complex of up to three species, and it has been observed that the presence of the wood borer Agrilus biguttatus Fabricius 1776 can amplify the symptoms. Practical implication: The amount that each stressor contributes towards these declines and the ‘tipping points’ are largely unknown and are likely to differ between decline events, sites and even individual trees. This makes management advice provision exceedingly difficult. Historic records show oaks in decline can recover; therefore, allowing trees time and space to recover should be a priority for management practitioners. Future research recommendations for effective management of declining oaks are discussed.

Botanic gardens host diverse living plant collections and are increasingly recognized as sentinel sites for documenting insect biodiversity and detecting biological invasions. Aphids (Hemiptera: Aphididae) are well suited to such monitoring due to their close host associations, rapid population growth, and importance as horticultural pests and virus vectors. Here, we document the aphid fauna recorded in five European botanic gardens—Zabrze (Poland), Meise (Belgium), and the Royal Botanic Gardens in Edinburgh, Benmore, and Logan (UK)—based on surveys conducted in 2022 and 2023. Sampling approaches included short-duration expert bioblitz-style surveys and extended seasonal monitoring. In total, more than one hundred aphid species were recorded across all sites. Observed species lists differed among gardens and survey periods, reflecting variation in sampling timing, intensity, and host plant composition. Several alien aphid species to Europe of Oriental and Nearctic origin were detected, including multiple new national records. Alien taxa were found both in outdoor living collections and in controlled environments such as glasshouses, nurseries, restricted areas, and plant shops, which may function as entry points as well as locations for early intervention. These findings illustrate the value of botanic gardens for documenting aphid diversity and supporting early detection of non-native species relevant to plant health and biosecurity.

The introduction of alien insect species is increasingly facilitated by global plant trade, particularly through the movement of ornamental plants. Takecallis nigroantennatus, a host-specific aphid associated with cold-hardy Fargesia bamboo, has recently expanded its range in Europe. To examine its invasion dynamics, we conducted a population-level survey across 13 locations in six countries, sampling individuals from botanic and private gardens, specialized bamboo nurseries, garden centers, and urban horticultural environments in the UK, Belgium, The Netherlands, Germany, Poland, and Norway. A total of 117 specimens were analyzed using mitochondrial COI sequences, revealing a single dominant haplotype without geographic structure based on Bayesian and Maximum Likelihood phylogenetic analyses. This striking genetic uniformity indicates a narrow introduction bottleneck, suggesting a single or highly restricted introduction event followed by clonal spread. Despite the species’ ability for sexual reproduction, the data support a founder effect and rapid recent expansion closely linked to the introduction history of Fargesia in Europe. The results are also consistent with a possible time lag between the arrival of ornamental bamboo and the subsequent establishment of its associated herbivore, a scenario that warrants further investigation. Importantly, our study provides a practical framework for applied monitoring and early detection in bamboo nurseries, botanical gardens, and other high-risk introduction sites, illustrating how molecular tools can inform biosecurity and the management of emerging invasive species.

Ilex spp. (holly) are widely planted ornamental evergreen shrubs which perform both an aesthetic and an ecological function in gardens. In Edinburgh, I. aquifolium is the second most common tree after Acer pseudoplatanus (sycamore), providing food and shelter for a range of species. Unfortunately, holly is under attack from a disease caused by the pathogen Phytophthora ilicis. This understudied pathogen has been in the UK for at least 35 years, but the impact has not been clearly elucidated. We undertook a study at the Royal Botanic Garden Edinburgh to understand the impact of this disease on Ilex spp. within a botanical plant collection. Our survey showed 14% of the collection was confirmed to be infected with P. ilicis, although true prevalence is probably underrepresented due to seasonal factors and detection challenges. We discuss possible management strategies for this disease.