http://cals.arizona.edu/yavapai/anr/...nglishivy.html

While English ivy cultivars are excellent accent plants in containers,
plain old English ivy is not the most desirable landscape plant. Some
of its problems include damage to structures from rootlets, creating
refuge areas for pests (undesirable insects and rodents), and invasion
into natural areas where it displaces native vegetation. English ivy
is also poisonous. The cell sap causes severe skin irritation and the
berries and leaves are toxic if ingested.

English ivy can also damage trees when it climbs the trunk and
competes for water, nutrients, and light. Ivy climbing trees should be
carefully removed to avoid damage to the tree trunk and cleared away
from the soil at the base of the tree. This is not as easy as it
sounds because ivy roots can become closely intertwined with the tree
roots. I suggest clearing ivy away from the trunk for at least a three
foot distance.