Ubiquitious Phytophthora infestations of forest, horticultural and ornamental nurseries and plantings demonstrate major failure of plant biosecurity in Europe

Large-scale Phytophthora surveys in (1) forest nurseries, advanced tree nurseries, horticultural nurseries and ornamental nurseries and (2) forest, riparian, amenity, landscape and ornamental plantings and horticultural plantations were conducted by 32 research groups in 21 European countries between 1977 and 2012 with most surveys dating from after 2000. Over all countries and nursery types, 1283 out of 1620 nursery fields and container stands (79.2%) in 563 out of 601 nurseries (93.7%) were found infested by a total of 40 different species and designated taxa of Phytophthora. In most nurseries highly deleterious host-Phytophthora combinations were found, eg. Alnus spp. and P. alni; Quercus spp. and P. cambivora, P. cinnamomi, P. quercina and/or P. plurivora; Castanea sativa and P. cambivora and/or P. cinnamomi; Fagus sylvatica and P. cactorum, P. cambivora and/or P. plurivora; Citrus spp. and P. citrophthora and/or P. nicotianae; Rhododendron and P. cinnamomi, P. plurivora and/or P. ramorum. In contrast to many southern European nurseries where wilting and dieback symptoms were quite common, most of the infested plants in intensely managed nurseries in Central and Western Europe with regular applications of several fungicides and fungistatic chemicals appeared visually healthy underpinning the uselessness of international plant health protocols that are primarily based on visual inspections. In the planting surveys a total of 48 Phytophthora taxa were recovered from 1498 of the 2353 tested plantings (63.6%) As with the nursery fields, plants were often infected by the most aggressive pathogens towards the respective host species. Infected plants often showed symptoms such as thinning, chlorosis and dieback of the crown, extensive fine root losses and collar rot. The average numbers of Phytophthora species/taxa per infested nursery and planting were 1.8 and 1.4, respectively. Thirty-two of the Phytophthora species/taxa detected are considered exotic invasive species. Amongst them P. cactorum, P. cambivora, P. cinnamomi, P. cryptogea, P. plurivora and P. quercina are widespread in Europe and must be considered as well established in both nurseries/plantations and mature stands. Several Phytophthora species/taxa have been found for the first time in Europe, ie. P. austrocedrae, P. gregata, P. humicola, P. quercetorum, P. rosacearum, P. taxon citricola 5 and 6, P. taxon organica and P. taxon gregata-like; while others have never or only rarely or regionally been recorded from mature stands, ie. P. kernoviae, P. lateralis, P. multivora, P. pini and P. ramorum. These apparently recent introductions demonstrate that alongside the exponentially increasing volume of imports of living plants from overseas to Europe the unintended introductions of Phytophthora species are also increasing dramatically. According to a conservative calculation 770000 infested forest plantings with a total area of 5.4 milllion hectares have been established in Europe between 1990 and 2010. Millions of infested landscape plantings and ornamental plantings in the urban-forest interface and tens of thousands of kilometers of roadside and riparian plantings of infested advanced trees and shrubs are completing the dense network of Phytophthora infestations across Europe. The findings of this and previous studies demonstrate major failure of plant biosecurity in Europe which will be discussed.