Doublefile Viburnum blossoms rival Dogwood trees
stress occurs, the fungus invades and causes cankers. It can enter
through wounds or through natural openings in the plant. Cankers
appear as sunken areas in the bark that usually expand lengthwise
down the stem. The bark in a cankered area may appear roughened; it
often cracks and splits, then pulls away from the stem - just as you
saw on your viburnum and are seeing on your neighbor's. When the
bark is cankered around a stem's circumference, the vascular system
that transports water and nutrients is broken and the stem dies.
Although woody plants can recover from drought stress, it does leave
its mark. For example, growth rings in woody plants are smaller in
dry years than in years with plentiful moisture. The hot, dry
weather we had this summer could have been the last straw for your
second viburnum, especially if you were not able to provide
irrigation during that period.
Winter injury can be expressed in a number of ways, including bark
Protecting viburnums from stress
• WATER - Provide an inch of water weekly when we get into
hot, dry weather.
• MULCH - Two to three inches of mulch around the base of
trees and shrubs to help conserve soil moisture, moderate soil
temperatures and keep lawnmowers and weed whackers away from the
trunks and stems.
• PRUNING - Be sure to make proper pruning cuts that protect
bark branch collars and avoid leaving stubs that create an excellent
opening for this fungus to gain entrance into the plant.
• TIMING - Allow plants to harden-off for winter properly; do
not prune or fertilize woody plants after mid-July to minimize
• MONITOR - Protect plants from insect or disease infestations
that result in defoliation.
There is no chemical control for
canker. Protecting plants from stress, and making sure that the
site meets an individual plant's cultural requirements reduces the
likelihood of plants being infested with botryosphaeria canker.
Prune out and destroy any infected branches or stems.