Abstract
Two diseases, Rhabdocline needle cast caused by Rhabdocline pseudotsugae Sydow, and Swiss needle cast caused by Phaeocryptopus gaeumannii (Rohde) Petr., recently became a severe threat to Central European Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) stands. Both pathogens infect assimilative organs causing needle chloritization and drop off. Pervasive infection by these pathogens has been recorded at the Hůrky provenance trial (Písek, South Bohemia, Czech Republic), established in 1971 as part of a series of experiments by International Union of Forest Research Organizations (IUFRO). The intensity and duration of needle cast sporulation were monitored using a Burkard spore trap, and the health status of 24 Douglas fir provenances from the original areal of distribution (British Columbia, Washington, Oregon) was evaluated under this trial. While comparing provenances, the following characteristics were surveyed: trunk volume, defoliation rate, and the difference in tree diameter between measurements in 2011 and 2016. A statistical evaluation was performed using the regression model and a decision tree. The highest sporulation rates on needles for both needle casts were observed from April to July. The Washington provenances 1069 North Bend, 1075 Enumclaw, and 1089 Cathlamet can be recommended for plantation, considering the provenances’ satisfactory productivity and low extent of damage from needle casts, while the provenances such as 1104 Brookings, 1028 Merritt (due to high mortality) and 1010 Barrière, 1021 D’Arcy, and 1067 Skykomish (due to high defoliation) are not suitable for plantation under Central European conditions.
Highlights
During an examination of stands health in the neighborhood of the Hůrky research trial (CzechRepublic) in 2012, infections of Douglas fir Pseudotsuga menziesii (Mirb.) Franco caused by pathogensRhabdocline pseudotsugae Sydow and Phaeocryptopus gaeumannii (Rohde) Petr. were recorded for the first time
The occurrence of P. gaeumannii based on the numbers of spores captured on adhesive tapes and in samples was much more frequent
The first finding was recorded in late May, and the strongest infection pressure occurred at the end of June and in early July
Summary
During an examination of stands health in the neighborhood of the Hůrky research trial (CzechRepublic) in 2012, infections of Douglas fir Pseudotsuga menziesii (Mirb.) Franco caused by pathogensRhabdocline pseudotsugae Sydow and Phaeocryptopus gaeumannii (Rohde) Petr. were recorded for the first time. The occurrences of both needle casts were directly observed during the research trial itself. Douglas fir has been introduced to Central Europe by forest managers for its high production of commercially valuable products and for its ability to stabilize forest stands, mainly against windthrow [2,3]. Various plantations of this species with undocumented origin were created in Europe during the 19th century, while first provenance-based research, oriented to survival rate, production, and quality, was performed in Germany in 1910 [4]. In comparison to Norway spruce, Douglas fir has a smaller effect on soil nutrients and has a positive effect on humus production, soil pH, and can regenerate naturally under suitable silvicultural treatments [2,5,6]
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