When mistletoe attaches to the oak’s branches, it siphons water and nutrients from the tree, which can reduce the tree’s overall health and vigor. As mistletoe grows, it can also create open wounds on the tree’s bark, making the oak more vulnerable to diseases and pests. If left unchecked, mistletoe infestations can lead to stunted growth, poor foliage, and in severe cases, the decline of the oak tree.