Diseases on Christmas trees in southern Sweden and western North Carolina - with emphasis on Phytophthora root rot and Neonectria canker

Surveys and inoculation experiments were conducted in Sweden and North Carolina to investigate diseases of Christmas trees, focusing on Phytophthora root rot and Neonectria canker. Christmas tree production is a significant business in North Carolina and for individual growers in Sweden. In North Carolina, six Phytophthora species were discovered on symptomatic Fraser fir (Abies fraseri), three of which were new to the region (P. europaea, P. citrophthora, and P. sansomeana). Phytophthora cinnamomi was the dominating species causing disease, but P. cryptogea also contributed significantly to Fraser fir loss. According to a questionnaire survey, 88% of Christmas tree growers had Phytophthora root rot in their fields. To combat Phytophthora root rot in North Carolina eastern white pine is planted on heavily infested sites as an alternative to Fraser fir. After screening eastern white pine families for P. cinnamomi tolerance, it is evident that families specifically selected for tolerance will reduce problems with Phytophthora root rot. In Sweden, 16 disease-causing pathogens and six pests were discovered in a survey of Christmas tree plantations. Further studies focused on Phytophthora root rot and Neonectria canker. Five identified Phytophthora species were isolated from waterways and soil samples. In addition, P. megasperma was isolated from a young diseased Norway spruce (Picea abies). Inoculation tests with P. cryptogea, P. megasperma, P. plurivora showed minor disease development. The Phytophthora species found were not widespread and it is currently a minor problem for Swedish Christmas tree growers. From Norway spruce trees with top-dieback, Neonectria fuckeliana was commonly isolated. On Nordmann fir, Neonectria neomacrospora was found. Inoculation studies using N. fuckeliana and N. neomacrospora on Norway spruce and Nordmann fir, respectively, demonstrated that both pathogens caused disease, while a second N. fuckeliana inoculation study found symptom development to be minor. For rapid and reliable identification of N. fuckeliana in northern Europe, a species-specific PCR-based test was developed