Formation and growth of stem cankers caused by Gremmeniella abietina on young Pinus contorta

From 1990 to 1995, the formation and growth of stem cankers caused by Gremm eniella abietina on Pinus contorta var. latifolia was studied in three stan ds in northern Sweden. The stands were planted in 1976-80. The total number of cankers on 756 trees that were individually followed increased from 233 to 477 during the 5-year period. With 42.0% of the cankers, the pathogen e ntered through or from the base of diseased branches, and 33.6% through vis ually undamaged bark. Most of the cankers were within 100 cm of the ground. In one of the three areas, the cankers were evenly distributed within 180 cm of the ground. The frequency of cankers facing north exceeded those faci ng south. The average vertical length of cankers had increased, 55.6% of ca nkers had increased their percentage coverage of the stem girth; 13.8% had fully girdled the stem. At two of the sites, there was a negative correlati on between canker coverage of the stem circumference and tree height increm ent.