Invasive alien species (IAS) are an important threat to forests. One of the best ways to manage potential IAS is through early detection and rapid response (EDRR) strategies. However, when dealing with IAS in forests, EU regulations are divided between phytosanitary regulations and IAS regulations. A version of EDRR for the former has been in place in the EU for more than 15 years while the latter is still in the process of being implemented. During 2019, a workshop was held to gather international experts on different plant health pests and IAS. The purpose of this workshop was to identify the opportunities and difficulties in applying the EDRR system in the EU phytosanitary and IAS legislation to four species for providing suggestions to improve the EDRR system. The model species are well known and come from different trophic levels. These species were the American pokeweed (Phytolacca americana), the grey squirrel (Sciurus carolinensis); and the plant health pests Geosmithia morbida and Emerald ash borer (Agrilus planipennis). We identified the similarities in the challenges of early detection, rapid response and communication of these species. For all species, difficulties in species identification, knowledge gaps on the pathways of spread, a lack of resources and uncertainty over which national government service was the competent authority were identified as the main challenges. Other challenges like public perception for the grey squirrel or methodological problems were species-specific. Regarding the rapid response: public perception, determination of the eradication area, sufficient scientific capacity and the lack of resources were common challenges for all species. Therefore, collaboration between institutes dealing with plant health pests and IAS can lead to better control of both groups of unwanted organisms in forests.