Weeping cherry trees (Prunus pendula) may develop gummosis, or oozing sap, as a symptom of an underlying condition. Stressful growing conditions; infected wounds; viral, bacterial and insect infestations; or cold-damaged bark are potential causes of gummosis in weeping cherries. Leucostoma cincta or Leuctostoma persoonii fungus enters the tree's wounds and forms sap-leaking Cytospora cankers. Untreated cankers may kill a tree's trunk or branches. Gummosis treatment includes remedial and preventive measures.
Prune the affected tree's cankered branches with the saw or lopping shears in late winter. Make the cuts at the branches' collars, where they join the trunk or other branches. Look for "wrinkled" bark to help you identify the collars. Cut just beyond the end of the collar further from the adjoining branch or trunk.
Burn, bury or dispose of the cankered branches where they won't infect other trees.
Use the paintbrush to coat the trunks and lower branches of young -- 1- to 3-year-old -- trees with the white latex paint before the first fall frost. This protects their bark from cold damage.
Prune your weeping cherries to shape only when they begin to leaf out in early spring. They heal most quickly at this time. Wait for dry weather and a temperature below 21.1 degrees Celsius (70 degrees Fahrenheit), when the Cytospora fungus is less active.
Request a professional soil test through your local university's laboratory. Follow the recommendations for soil drainage and nutrient amendments to improve your tree's health. If you test in late summer, delay fertilising the tree until the following spring.
Water the trees regularly during prolonged dry periods to reduce stress.
Avoid mowing or working around the base of your weeping cherry to protect the bark from accidental injury.