Gummosis is a fairly common disease of weeping cherry trees that can be caused by a bacterial or viral infection. The pathogens that cause gummosis enter a weeping cherry through wounds in its trunk or branches. Once infected, the wounds turn into cankers that ooze tree gum. The best treatment for gummosis is to improve the health of the tree to make it better able to fight off the infection.
Prune the tree limbs with the largest cankers in winter. Make the cut at the base of the limb, just above the collar (the swollen portion between the limb and its point of origin). Once you remove the limbs, burn them or bury them at least 3 feet deep to prevent the spread of the disease.
Paint the lower branches and trunk of weeping cherry trees that are between one and three years old with white latex paint to protect them from winter injury.
Avoid pruning or otherwise wounding the tree unnecessarily. If you must prune the tree to shape it, the horticulturalists at the University of Kentucky recommend waiting until early spring when the tree ends its dormancy. Weeping cherries are most susceptible to gummosis infection when the weather is moist and the temperature is between 70 and 85 degrees F. Do not prune or wound the tree during this time. When shaping a weeping cherry, prune away any branches that grow at less than a 45-degree angle. Narrow branch crotches are more likely to become infected.
Maintain the health of your weeping cherry. Remove any grass growing underneath the canopy of the tree, then spread 3 inches of mulch from the base of the tree (but not directly touching it) out to its drip line. Call your local county extension office to arrange to have a soil test conducted (for a nominal fee). The results will tell you exactly how much fertilizer you should be giving your weeping cherry.