Pitch canker caused by the fungus Fusarium subglutinans f.sp. Infection typically occurs in the upper portion in the crown in early winter to spring. At the site of infection pitch flow occurs as the tree responds to the fungus' presence. Infection will progress down the stem and this results in the flagging or reddening of shoots. The fungus is spread via the wind and rain and likes cool, moist conditions.
Infection therefore takes place in the late winter to early spring of the year.
Here is a canker that is producing the characteristic resin flow. Here is a branch that is covered and dripping in resin. The fungus responsible for the disease is a wound pathogen and thus some type of injury is required before infection takes place. One example of widespread infection occurred a few months after a severe ice storm damage the southeastern forests of Alabama. Other common wounds include insect feeding and oviposition damage.