Mitigating agricultural impacts of <i>Amaranthus palmeri</i> : A call for comprehensive management strategies to limit further spread across <scp>Europe</scp> and the <scp>Mediterranean</scp> region

Amaranthus palmeri S. Watson (Palmer amaranth) is a highly competitive, dioecious annual herb that is native to the southern US and Mexico, spreading rapidly beyond its original range, following introduction to Europe and the wider Mediterranean region (Kanatas et al., 2021; Mennan et al., 2021; Milani et al., 2021; Rubin & Matzrafi, 2015; Torra et al., 2020). According to 2017 and 2019 national surveys by the Weed Science Society of America (WSSA), A. palmeri poses a major threat to summer crops such as maize (Zea mays L.) and grain sorghum (Sorghum bicolor (L.) Moench.), leading to significant yield reductions even at low densities (van Wychen, 2017, 2019). Amaranthus palmeri is notorious for quickly developing resistance to herbicides at multiple sites of action (SoAs), with widespread resistance occurrence reported across a range of countries (Heap, 2024). The objective of this Special Issue is to enhance understanding of risks and impacts to agriculture of A. palmeri in Europe and the Mediterranean region. We have gathered research and review articles from various countries in these regions, along with contributions from researchers in the United States. The main themes of this issue revolve around the spread and occurrence of A. palmeri in these areas, competition with different crops, the evolution of herbicide resistance, and a detailed examination of its reproductive system and implications for distribution and strategies for management. Amaranthus palmeri is highly competitive, with studies from Turkey indicating that even a single plant per metre in a cotton row can significantly reduce cotton yield (Erbas et al., 2024). Higher densities of two and four plants per row were shown to have a substantial impact on cotton yield, reducing it by 51%–63% and 75%–79% respectively. This Special Issue reports several populations of herbicide resistant A. palmeri across the Mediterranean region. In Spain, a roadside population near Tarragona harbour showed no known mutations endowing glyphosate resistance at the 5-enolpyruvylshikimate-3-phosphate synthase EPSPS gene sequence among confirmed resistant plants, although specific molecular markers revealed the presence of the EPSPS cassette in 70% of tested plants (Manicardi et al., 2025). In Turkey, 18 of 21 A. palmeri populations collected from five provinces were categorised as less sensitive to glyphosate and acetolactate synthase (ALS) inhibitors, with dose–response data indicating a more than seven-fold resistance to glyphosate and 9- to 10-fold resistance to the ALS inhibitor nicosulfuron (Kaya-Altop et al., 2025). Similar to the findings from Spain (Manicardi et al., 2025), copy number variation is suspected as the main mechanism for glyphosate resistance in the populations collected from Turkey, while sequence alignment of the ALS gene revealed target-site resistance mutations, including Ala122Val and Pro197Arg, that are associated with resistance to ALS inhibitors (Kaya-Altop et al., 2025). In Israel, 22 A. palmeri populations collected from agricultural fields were tested for resistance to glyphosate and the ALS inhibitor, trifloxysulfuron, and it was found that although several populations exhibited reduced response to glyphosate, dose–response assays did not confirm resistance to the recommended labelled field rate, and there was a high level of resistance to trifloxysulfuron, where four populations tested under dose–response studies survived up to four times the recommended labelled field rate, likely due to a Trp574 Leu mutation of the ALS gene (Abu-Nassar et al., 2025). As a newly invasive species in some countries of Europe and the Mediterranean region, the identification of A. palmeri and rapid detection of invasion events are critical for its management. Matzrafi et al. (2025) reviewed key botanical traits that allow differentiation of A. palmeri from other closely related Amaranthus species, and assessed future risks of its invasion and spread based on climate conditions and agricultural practices, with an overview of strategies for early detection, along with chemical and non-chemical weed control methods for effective management. The role of various ecological, physiological and genetic traits of species is crucial for understanding their potential for invasion and establishment. Borgato et al. (2025) reviewed how genetic and genomic characteristics of A. palmeri may interact with aspects of its reproductive biology, including its breeding system that may potentially enhance the likelihood of hybridization and development of herbicide resistance; this understanding is particularly significant, given the presence of other Amaranthus species in Europe and the Mediterranean region. The authors also discussed the breeding system of A. palmeri in the context of weed management, highlighting innovative approaches such as irradiated pollens, genetic manipulations and RNA interference (Borgato et al., 2025). In conclusion, this Special Issue highlights the significant risks and impact of A. palmeri invasion to agriculture across Europe and the Mediterranean region. However, a number of knowledge gaps remain and it is crucial to deepen our understanding of the fundamental biological traits that facilitate invasion and establishment success of this species, as well as to future-proof integrated weed management programmes. While substantial emphasis has been placed on understanding the mechanisms related to resistance to different SoAs, there is an urgent need to design effective management strategies for the limitation and mitigation of ongoing and future impacts of A. palmeri on agricultural systems. Options may include legislation to restrict the exchange of agricultural products among countries in the region to prevent local spread, especially of herbicide-resistant populations. Given the current trends in herbicide resistance, enhanced collaboration among researchers, policymakers and agricultural stakeholders is essential for developing comprehensive management strategies that take into account the complex interactions between A. palmeri and its environment. Joel Torra acknowledges the support by the research network PalmerNET Grant RED2022-134285-T funded by MICIU/AEI/10.13039/501100011033, and also by the Ramon y Cajal Grant RYC2018-023866-I funded by ‘ESF Investing in your future’. Husrev Mennan thanks TUBITAK for support with project number TOVAG 123O021. The authors declare no conflicts of interest. The peer review history for this article is available at https://www.webofscience.com/api/gateway/wos/peer-review/10.1111/wre.12675.