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From 1987–1991, conditions in 110 conventional plantings of introduced lodgepole pine (Pinuscontorta Dougl. ex Loud.) were investigated in northern Sweden. Severe damage by Scleroderris canker, caused by the fungus Gremmeniellaabietina (Lagerb.) Morelet, was recorded at high elevations in 1987. Damage was related to a period with extreme weather conditions. The disease was initially severe in low lying areas, from where it quickly spread throughout the plantations during 1988. Temperatures above average during 1988–1990 favoured tree vigour, which in turn slowed the spread of the disease. The frequency of stem cankers increased in seriously infected areas during 1989, and new severe damage was recorded locally in 1990 and in 1992. A strong correlation was found between disease severity and the temperature sum at the site. Lodgepole pine planted on spruce sites was often severely affected. A negative correlation was found between the frequency of G. abietina and the abundance of birch thicket. In large areas in northern Sweden with a more favourable climate, lodgepole pine plantations were healthy and productive up to 1991. However, instability, leading to increased susceptibility to disease, has become a problem of great concern in some of these areas during the 1990s.

No abstract

The design of the Swedish National Forest Inventory as well as the National Forest Damage Inventory is a sparse sample of systematically allocated plots. In this study data were combined from these two independent inventories to estimate geographical distribution, area extension, and disease development of a Gremmeniella abietina (Lagerb.) Morelet epidemic. For the combined data the standard error for estimated total area of affected Scots pine (Pinus sylvestris L.) and lodgepole pine (Pinus contorta Dougl. ex Loud. var.latifolia Engelm.) forests was about 11%. Assessments of the proportion of pine trees with fresh shoot blight infection shows that changes larger than 1% are significantly (p < 0.05) estimated. By testing in pairwise cross inventory, it was shown that the accuracy of the assessment of total shoot blight symptoms was fairly good in 2001–2002, with a κ statistic of 0.59–0.61. Severely damaged trees were identified with an agreement of κ = 0.81. The total area of pine forest both slightly and severely affected by G. abietina during 2001–2003 was estimated to be 484 000 ha. Three geographically separate damage centres were distinguished. Thus, despite a relatively sparse sample plot density, the national forest inventories have good potential for estimating the geographical distribution, areal extent, and dispersal of extensive damage outbreak. Results are dependent on the inventories being carried out with an accurate identification of target objects.

Survival and vitality of Gremmeniella abietina on Pinus sylvestris slash was studied in northern Sweden during 2003 and 2004. Once a month between September 2003 and April 2004, two to three trees were cut down and debranched. Shoots with pycnidia were sampled at the felling date and then at every consecutive month. The percentage of germinated conidia from each shoot was calculated after 24, 48 and 72 h incubation. The vitality of G. abietina pycnidia in the slash remained high the whole period. Intact pycnidia were found on slash several months after the time of conidial sporulation, which indicates that new pycnidia may be produced on dead pine branches. Sampling of shoots from slash on 13-to 18-month-old clear-cuts showed conidial germination capacity as high as in pycnidia collected in fresh slash. Due to survival of G. abietina in slash it is recommended to postpone planting of P. sylvestris seedlings in northern boreal areas to the third vegetation period after sanitary clear-cuts.