The effect of European canker and its spatial pattern on four apple cultivars in British Columbia.
The density and distribution of Nectria galligena were determined on all 16 combinations of 4 cvs (Summerland Red McIntosh, Harrold's Delicious, Spartan and Golden Delicious) as scions and interstocks, all on M.9 rootstock in an orchard of 10-year-old trees in British Columbia. The interstock cv. had no effect on tree mortality but there were large scion cv. effects. Trees of Summerland Red McIntosh and Harrold's Delicious were quite susceptible to buildup of canker and subsequent death, whereas the other cvs were relatively resistant. The number of cankers/tree was significantly related to the sum of the cankers on the 8 surrounding neighbours of each tree. Trunk cross-sectional area was significantly correlated with the number of cankers/tree in Summerland Red McIntosh and Spartan. However, differences in tree size alone did not account for the differences in numbers of cankers on the 4 scion cvs.