Collar or crown rot is caused by a fungus that invades a tree’s lower trunk or upper roots and begins to block the tree’s vascular system. The infection point often develops as a canker which causes a girdling (strangulation) of the tree as it spreads. Crown rot and collar rot refer to the same disease, except they have different names depending on the location of the infection (on the root stock or the scion portion of the graft union). The most obvious symptom found on an infected tree is a partial or complete girdling of the trunk. The diseased tissue at first appears orange and reddishbrown, then becomes browner as the rot and decay advances. The disease spread is most prevalent in areas that have poor drainage or standing water.